Comparative anatomy of the pectoral girdle and upper forelimb in man and the lower primates

Item Type text; Thesis-Reproduction (electronic)

Authors Barter, James T.

Publisher The University of Arizona.

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Link to Item http://hdl.handle.net/10150/551254 COMPARATIVE ANATOMY OF THE PECTORAL GIRDLE AND UPPER FORELIMB IN MAN AND THE LOWER PRIMATES

by James T. Barter

A Thesis submitted to the faculty of the Department of Anthropology

in partial fulfillment of the requirements for the degree of MASTER OF ARTS in the Graduate College, University of Arizona

1955

Approved: Director of Thesis

ET'-H " r n s r - r

This thesis has been submitted in partial fnlfillment o f' require­ ments for an advanced, degree at the University of Arizona and is deposited in the Library to be made available to borrowers under rules of the Library» Brief quotations from this thesis are allowable without special permission, provided that accurate- acknowledgment of source is made* Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major depart­ ment or the dean of the Graduate College when in their judgment the proposed use of the; material is in the interests of scholar­ ship* In a ll other instances, however, permission must be obtained from the author*

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T- : i Table of Contents:

' : " . ' ." . ■ 1 ' : ; ; ; " " : Page : - ;" ■; . , .■ ' ■ . , , ■ : ■ - 4' ' JEO.S'b Of ^3e5l*b©S o o o ,o <> o o ,<> o o 6 o-"... o o o b - o o o 2LV

Chapter 1 2jl"bZ6 OCltlO *b2.0n e o o o o o o o o o • o o o o o o o o o e 6 1 Ac knowl 6Q,g omsri'bs o 6 o o o • o o © © o ©- © . © © o © © 3.0 Chapter 2 Ehterials and Methods = » ofV. o » <, « <,000 0 .«>. <, = 11 Chapter 3 Descriptive Myology of the Beet oral Girdle 0 0 0 0 <, » 15

Ao Muscles connecting the upper extremity, . - to the vertebral colnamo Trapeziuso 0 0000 0 0 0 0 0 0 0 0 0 0 - & © 1^

- Datissimus dorsi ©0 0 © » © « » # © © , © © © 1 8

Idiombdidens © © © 000 © 0 © » © © © 0 © © » 21 ./lievatof scapulae ©: © ;© © © © © © © © © © © © 23

^ Qmoc ervicalxs © © © © © © © © © © © © © © © © 23 B© Muscles connecting the upper extremity to the anterior and lateral thoracic walls© Feetoralxs ma^or © -© © © © © © © © © © © © © 2(S Pectoralis minor © © © © © © © © © © © © © © 28 Pectoralis abdominalis © © © © © © © © © © © 30

o3*s,v ilxxs © 0 0 0 0 0 0 0 0 0 0 0 0 0 0 b ■ 0 3^3

Serratus anterior o * o o o o o o o o o o o o 31 Co Muscles of the shouldere

Beltoxdeus o o o- o o * oo <> © o o o o o © <> 3^-j- leres miLnor o • 0 ■ 0 © ^ © ©

Supraspinatus© © © © © © © © © © © © © © © © , 39 XHf ^SrSpXIlSt^llS O o o O 0 O O o » O 0 " O O C O t> 6 »1|3. Sllfc) SC3.pTtX3.Z*XS <9 o o O o d O O O O O O o O 0 6 0 1|?2 Do Muscles of the upper anno ' , Goracobrachialxs o. o & o & o o 000.0 o o o ii-3 Daceps hrach%% o <> 0 o 0 0 0 o 0 & 0 0 0 0 o 0 Drachn.alzL s 0000 0 <> o o <> o o o o 0 0 <> 0 0

IrxcepSo o o o. o o -- o 0000 o 0 0 o o o o o © I48

Dorsoepitrochleariso © © © ©. © © © © © » © © © 51 Chapter h Comparative Morphology- of the Brachial Plexus * © © © ©. 6$

Baboon© © o © o © © © © © © 0 © © © © © © © © © 00

Gibbon © © © .© © © © © © © © © © . © © © © © © o ,6^

Chnmpansee © © © © © © © © © © © © © © © © © © *71 btmaary © © © © © © © © © © © © © © © © © © © © YI4.

Chapter 5 Comparative Osteology © © © © © © © © © © © © © © © © © 78 Scapula© © • © © © © © © ■ © - © © ©,© © © © © © © o 78 C lavicle o © © © © © 0 0 © © © © © © © © © © © 82

Humeruso © © © o .© © Comparative Structure of the Pectoral Girdle © 87 Chapter 6 Oomparative Myology and Function© © © © © © © © © © © © 95 A© Muscles connecting the upper extremity to the vertebral column©

Trapezius0 <= o . © © © © © © O O 0 0 © © © 101

Latissimus dorsl,» O © © © © © 0 © © 0 0 0 © © 103

Bhambdideuso 0 ®" O © Q O © O © © 0 O © O'© 0 105 OraocervicaliSo 0 « © 0 0 © 0 © © O © © 0 © © 1Q7

Levator scapulae c ■ *■ © © © O © O © O 0 0 0 © 0: IO9 B0 Muscles connecting the tipper extremity to the anterior and lateral thoracic walls« Pectoralas major , o o o o e o ^000000000 110

Pectoralis munor 0 0 o o o o o o <> o o o o o l i t Pectoralis abdominalis 0 , 0 0 .« » 115 SilbclaVlUS O-OO© O GOO o o o o o o o o o 116

Serratus anterior © © © ® © o 0. 0 000000 116 Co - Hmscles of the sho'alder0

Deltoa-dens © © © 0 0 o o o o o o. 0 0 6 6 0 e 118

Teres minoro 0 0 0 o ® o 00 o o o o o o o o 120

Teres major® 0 0 0 0 o © 0 © © © o o o o o o 121

Supra spina tus © © © © © o..©: ©. © © O 0 0 0 6 O. 122

Infraspinatus© >. © ©; o © .® © © © 4 G 0© *^;:© 123 Sub sc apularis = © © O G o <9 0 o 0 0 o o p e o 12lt D© Muscles of the upper aim

Coracobrachialis , © © © © © © © o o o 0 0 o I 2I4.

Biceps brachii© © ® © © © © :© © o 0 o bo. P 126

BhachialiS © ,©■ © © © © © © © © © O 0 0 o p o 12?

Triceps © © © © © © © © © © © © © 0 0 o o d o .128

Dorsoepitrochlearis o o o 000 o 000 o o o 129

Chapter 7 Summary and Conclusions © © © © © © © © © 0 0 o o o o 132;

Bib liography © © © © © © ©■ © © © © © © © © o o o 0 0 o 136 .§ List of Plates Page.

Plate 1 ;Superficial pectoral musculature of an adult - female' 'baboon® © « ©■ o = " •• <•«. •.. « 53^

Plate 2 Superf i c ial dorsal - musculature of an adult V - ■ • female Latoou* o © ««»•.«. ■<>. © © - © © © © ^ © L©: © © 51t Plate 3 Superficial, dorsal musculature of an adult

. f g x b b o n .0 ••• O v. © O o o : e O . \o <> .o'- o o 0 0 0 . 0 ‘ o o o o o

• Plate i). • Superficial ■pectoral musculature of the left side , ' - ■ ' - . of an immature male chimpanzee © © © © © <, ■ © © © '« © © © '. £6 Plate '5" ‘ ^ Superfielal dorsal musculature of 'the left- side., ; ' ■% : of an immature male chimpanzee. « © © © - © © © © ■© ©' © © © 57

Plate 6 Superficial peGtoral musculature © © © o o d o o d '

Plate 9 Deep Dorsal 'musculature©: t i '©^©---©i©' ©. I s; Plate 10 Intrinsic m^ of the scapula © © © © © © © © © © 6 2 Plate 11 Intrinsic musculature of the ventral surface of 1 th e scapula © ©. ©- ©. © • © • © © © ©■ > © ©.©■.© -,© © ©.-©"©©- © ©- © 63

Plate 12 Brachial flex o r muscles© © © ©. » ■©, a ©; © © © V© © - © © © © 6h

. Plate 13 Left brachial plexus of the baboon, and gibbon© - © -© ;.© .©, o © ; 7.6 ..

Plate 1% : Left brachial plexus' of . the chimpanzee and man © © © © . d « ' :77:::%77 ; CO ON E late 15 Scapulae of the gibbons . baboon? and rhesus © © © © » :© .® « - 89 • P late 16 :- Scapulae : Left; htimeri of adult .prisates© i©: ©- ©. © © © © > © © 92

P late 19 The trhhM skeleton of four primates reduced to the , -v same to ta l length© ... © © © ©- © .© © © . ©-,;»\©-':«-:t^;-93: y llate: 20.;:;. Superior '.view;' d f the thorax and le ft; shoulder girdle -©-a ’ . 9k

- ' Shapter One Introduction The scientific investigation of man1s kinships to his “poor relations'* has had a long and varied history0 The Greek; physician Galens whose writings formed the basis of the science of anatomy for over a thousand years* based much of his knowledge of human structure on dissections of the Barbary apeo The first scientific comparative anatomy o f. man and the apes was published by Tyson in 1699* who des­ cribed the anatomy of an infant chimpanzee o At th is time and up to about the time of Darwin* authors made much of the man-like qualities of the anthropoid apes* and the implication at least was that the apes and man were in some, way relatedo I t remained for Linneaus (A0Do 1?58) to correctly place man among the mammals as a member of the order

Primates * a position he has w illingly or .unwillingly held. to . this e day0 The next major decision which confronted the taxonomists was that of man' s exact relationship to the-other primates» Thomas Huxley squarely faced the problem when he asserted that the similarities between the great apes and man were far greater than those between the great apes and the lower primates» However* he did not lose sight of the fact that there were significant differences between the apes and man* . differences of such degree as to necessitate placing man in a separate family (passim* Huxley* 1863). Bight years later Darwin lent the weight of his great reputation t© the furtherance of these ideas in his volume* The Descent of Man. ' - - " - /

. There was one concept which was im plicit in the writings of both ; : ' v; :/ : 2 these men, that ©f an ©rthogenetic phylogemy far the ajaeestry of man* Meirewer, the litin g primates were viewed as representing a gradated series of the stages of development through which man had passed in : his development» Available evidence today does not support snob a. uniserial.view of man’s deseettto . The development of the ideas of Huxley and Darwin have led to the orthodox view of today which maintains that man has been derived from an animal which would be structurally id en tified as an ■1fapens • • although perhaps we would not readily c la ssify th is animal, as a g o r illa or a gibbon o It is generally conceded that all the existing great apes have become highly specialized as a result of early adaptations to a new environment o . One problemc, which has vexed the followers of the orthodox school,, is that of the degree of affinity between man and the living anthropoids^ and the probable nature of the Common ancestor from which they have developed^ These speculations have culminated in the publishing of many "family” trees of man by such authorities as Gregory, Keith and Schultzo

The orthodox view has not gone unchallenged,, Even in the post- .

'Darwinian era there were c r itic s of the anthropoid ape theory to be found* Hivert (3.8?3)s for exampledenied that man had special affinites with any one primates but that in generals he shared certain characteris­ tics with many forms including the prosimians and eatarrhine monkeys e S t ill la te r s there were those, such as Osbora, who repudiated the orthodox view* He was certain that he had found paleontological evidence which indicated that the human ..line had separated^ as far back as the ' -

Oligocene period, from the mammaiian stock which cttliiiinated in the

anthropoid apes (1927ii.8l"j4.88)o Itf should he mentipried that another paleontologists Bovles re« . jected .the anthropoid ape ancestry of man on the basis of his studies ; of Neanderthal mane He thought that this form bore many more similar­ it ie s to the monkeys than he did to the apes (1911s 111^172j 1912 s 85-190) ; One of the most authoritative and persistant critics of the - ■ orthodox view- is Wood Jonese He has constantly reiterated his belief that man. has no community .of lineage with any of the higher primates*. '

It is h is h e lie f that man. sprang d irectly from the Etipene Tarsioids ands therefore^ that roan8 s closest contemporary kin i s the tiny Tarsius (.1923) There should be some common ground upon which - these two co n flic t- ing groups could stands even though the extremes are perhaps irreconcil- ableo That: so many spepialists of repute should have found serious difficulties with the orthodox view demands-. that we carefully, examine' the'premises upon tdiich this theory is founded® ' ' • The major evidence which the exponents of the anthropoid ape theory of manis origin have presented,, relates to the undoubted

similarities: between man and the anthropoid apes* Features of morphology, physiologys biochemistry, embryology^ and, psychology have been explored 7 . for , the^ various .likenesses .which are common to the highest primatess

Schultw .(1936) went to great lengths to illustrate that man and the apes

shared a larger number of morphological traits in common than any one of them did_ with the lower catarrhinesc. - ' ■. - - . / : ■: %. fhe dissenters haw tended to stress the great extent to which man is uaspeciaiized and has thus avoided the path followed by the higher primatess Such specializations as are recognized are considered . to be pH relatively recent origin and to indicate a trend away from the

direction pursued by the apes o' Such sim ilarities between man and the

great apes as do exist are explained away on the basis of parallelism« On the other hand. 1 anatomical sim ilarities between man and the lower primates have been eagerly seized upon as proof of the closer relation^ ship which ex ists between these forms 0 "; The counterargument ,t© this reasoning has been that the differences -between man and the apes are differences, of degree rather than kind* Many of the so-called unique specializations of man have been pointed. out to occur as variants more or less frequently an ong the great apes* In addition-; definite anthropoid ape features are commonly found •throughout mankindo ■/ ■ • : - ' ' ' V • ' . - • . ■ Another factor, which must be considered in the assessment of. the

divergence between man and the anthropoid apes j, is that of ewolmtionazy rate and associated time factors* Among the apes there is a much . ■ ■ ■ ■ ; . ■ -■ , . younger age at which puberty is reached, and thus the rate of reproduc­ tion i s greatly speeded' up* . At le a st th is i s so today, and presumably . a similar situation existed in the past, although not as pronouncedc Thus in a given time, there w ill be many more generations of apes, and if a greater evolutionary rate existed as welly and it may have, it is not surprising that the anthropoid apes have diverged relatively more from the primitive ancestral type* ~ 5 It cannot be doubted that man does- possess in 'his makeup features whiph are common to one or more of the so-called lower pri= . matese Perhaps I t depends upon the amount of weight which an individual investigator places on a given structure which determines his personal

view of phylogenyv Or it may hes as Straus (l?l|.9:207) has pointed out5 a matter of semantics^ a lack of common definition- of what is meant by

the teim ^ape” or “monlcey61» There is a possiblity that Washburn has provided us with a means whereby these opposing views could be reconciled, in his ideas con­ cerning radiations* ,?The origin of the primates was primarily a loco­ motor adaptationoo* The second (radiation) was a reorgani­ sation of the special sensesg making the monkeys successful in the Old World tropical forests'by day* The third radiation of Old World primat es depended again on a locomotor adaptation* In the apess a series of modifica­ tions in the arms and trunk leads to locomotion of a sort not found in the quadrupedal monkeyso o o ■ ^ ^If modern man be examined* ‘ he i s found to be a mixture of basic primate features^ the primary characters of the first or lemureid radiation. (The hands show a , remarkable amount of the primitive grasping adaptation with long digits nails* etc * It should be remembered that the most perfectly opposable and relatively largest thumbs among, a ll the primates are found in the lorises* and not in man* as often stated* Human feet are a recent modification of the same .pattern* fundamentally differing only in a single ligament and the length of the toes*) The next complex is that of the head* brain and special senses which is achieved* except for changes in propor­ tions* in the monkey radiation* Then the arms and trunk become essen tia lly modem* Perhaps then* many m illions of years later* the bipedal complex was developed. Finally* the secondary features of the human radiation became, general* the small face and the large brain*” . ".v. . (iSdtis*>9)'

If we adopted Wood Jones hypothesis * we would have to ascribe to parallelism a ll the higher primate characteristics which man shares with , ■■ ■-/ ■' . 6 , ; the moHkeys and apeso A similar conclusion has to be drawn if we accept Straus8s declaration that man is most closely allied to the catarrhine monkeys a Hew ever ^ following Washburn s the variations in interpretation of human phytogeny can be expressed in terms of the particular radiation from which a primary characteristic has been re­ tained® This view seems to be more preferable than that which r e lie s upon a single elrolutienazy process to explain all the similarities between man and the higher primates0 p Thus an investigator who examines the comparative structural features of the hand w ill find many characteristics of the grasping hand of the lemurs, -which have been retained by the higher catarrhine monkeys and mano However? i t would be readily apparent that the similarities- between the hand of man and the braehiating apes would not be as Obvious because the latter has become secondarily specialised! whereas^ the fomer has maintained its primitive characteristics* Structural comparison of primate hands i s one of the prime b its of evidence upon ■which Straus has based his determination of man's relationship with the catarrhine monkeys®(I9k9s 211)=

If a worker compares primarily the anatomical structure of the pectoral girdle/ he w ill note many characteristics which man shares in common; with the braehiating apes* Man* s affinity with the anthropoid apes i s demonstrated by such changes as the relative increase in size of the serratus anterior and deltoid muscles, the migration of the insertion' of the pectoralis minor muscle onto the coracoid process of the scapula? the extensive clavicular attachment of the pectoralis major? the increase in extent of the origin and insertion of the flexors and a corres­ ponding decrease in the extensors of the arm* ; These are characteristics

retained from the third radiation* The paleontological proof of this theory -is largely lacking* The record is not complete and perhaps w ill never be for some forms^ thus/ we may always have to rely to a certain extent npon comparative studies of the living' primates which should/ however, embrace all the possible '

fields of investigation* Some of the most complete knowledge of the non-human primates which we possess is in the field of gross anatomy^ yet even here, the accomplishments are scarcely noticable* Undoubtedly, we know more about the anatomy of the common cat than we do for any of the; non-human primates* The study of the gross anatomy of the lower primates approxi­ mates the stage human .anatomy had reached at the time of Versalius* ¥e have a few systematic studies for the anthropoid-apes (Sonntag,; 1923j Gregory, 1950), for several of the Old World monkeys (Polak, 1908j Hartman and Straus, 1933), for one of the Mew World monkeys (Beattie, 1927), for the tarsier, (Wpllards 1925), and for the lemur (Murie and Mivart, 1872)»- . -

• Many of these studies are generally. unavailable, having; been out of print'for a number of years or else found only in the larger anatomical libraries* The inadequacy of these anatomies have been :

accentuated because only one or two specimens were dissected* Perhaps, the scarcity of specimens has done more to retard the field of non­ human primate anatomy than, any other factor* Schultz (1950a) has pre­

sented evidence which indicates that there is a far greater range of - variability a»ong any group of the primates than has been previously supposed^ Thus;, results or far reaching conclusions based on the dissection of only one animal should be suspect* Some comprehensive studies have also been done on regional anatomys especially of the extremitieso The hand and foot have re­ ceived considerable attention (Straus,, 19^0, 19iils 19k2.$ Mortons 192lt| Gregory,, 19l6s 1928), as has the facial musculature (Huber, 1931 )s brachial flexor musculature (Howell and Straus, 1931), the pelvic musculature (Waterman, 1929), and the pectoral musculature (Miller, 1932)4 / - V : i . • ' ' V;; ' , : Some of these studies are lacking in specific details, being confined mainly to the presentation of differences and conclusions without describing the musculature in any detail0

Straus (1953) has written an excellent summary of the present status of primate anatomy and physiology* It is not the purpose of this introduction to repeat this surveys therefore, only a few points bearing on the current research have been coveredo

There has been one rather extensive study of the pectoral girdle among the primates (ELller, 1932) 0 It is an admirable survey, but no details of her numerous dissections are given<, For example, the anatomy of the wooley, spider, and capuchin.monkey is. a l l summarised under the heading of New World monkeys with no mention of any of the differences between these forms*, This failure to present the basic data is regrettable, especially because so little is known about the individual structural details of these forms = That such lack of ■ : ' • . ' : 9 presentation of details has, lessened the value of this article to other sc ien tific workers i s reflected in the fact that the report is rarely found as a reference in other primatologlcal studies0 Another criticism of this study might reflect ©n its assumption of an orthogenetic phylogeny for the evolution of the primates. In this> however^ she was following Keith5 one of the foremost primato- logists and evolutionists of the days This basic premise does, j lim it the usefulness of some of her conclusions<> Howell and Straus (IPS!) have published an excellent phylogenetic study of the brachial flexor muscleso Certain aspects of the muscula­ ture in this study are presented in good details but it is deficient because the muscles-were not related to other structures, in. the arm0

This does not detract from the usefulness of the article and it stands as one of the most thorough studies on the brachial musculatures The curreat problem was undertaken for two main purposes0 One was to ascertain the extent of the. similarities and differences between man and several of the lower primates in the structure of the pectoral girdle. In this respect, the study was conceived of as being a descriptive, comparative anatony of the more-important anatomical structures. The second purpose was concerned with ascertaining the differences in function which were correlated with the differences in origin and insertion of each particular muscle. 10 ‘ . . Acknowledgments ' ' '' -1 wish to thank Bertram S» Kraus for /suggesting the problera5 and William Brown and. John Schwartzman for a careful reading of the manu- ^ script and numerous helpful suggestions0

The specimens, laboratory spacer film; and photographic equipment were made available -by Emil ¥» Hamry3 Head of the Department of Anthropology of■the.University of Arizona0

3®** Lo Fo H0 Lowe assisted materially Joy developing' films and • ; _ pointing the negatives* .... I especially wish to acknowledge the '/many contributions of Bonnie Jones; without whose assistance this work would have been much less ' . ’ thorougho . ' 7 I am. also indebted to the members of my thesis committees Clara

Lee Tanner^ Emil ¥= Haurys and So B0 Danson for th eir numberous suggestions and careful proofreading of the manuscripto . 11. Chapter Two Materials and Methods ■ One of the major problems facing any student of non-human primate anatomy who wishes to further h is knowledge by actual dissection i s the lack of available speeimenso Dissectors of any of the non^human

primates have to content themselves with study of one or two representa­ tiv e s'o f any species such as are found in zoos* These are usually one of the higher primateso Every member of a species is representative of a ll other members of that species* Yet no one animal can be regarded as identical with all the other members of his species because of the effects of differing ■ heredity and environment* In addition^ morphology d iffers sign ifican tly with the age of an individual0 Therefore, entirely accurate comparisons ■ cannot ,: be made between the young of one species and the adult of another unless care is taken to keep this factor constantly in mind* The following classification gives the systematic position of the forms studied in the current research (after Straus,. 19U98 201)0 ' Order PEimTES „ . . Suborder PITHEGOIDm Infraorder CATARBHIME'

-- - Family . GERGOPHHBOlDiE ' - ' • : ' Genus MAGACA'

Oommon name - Rhesus Genus PAP10

Common name = Baboon 12 Familj EffiOMTami

■ : ■■■■:■ ■ . ■ ■■■ ' ■■ Benus HTEtOBAm : Ooimtion natoe =■ Gibbon fam ily PG1SIDAE Genus PAH - : ^ Gommon name ~ Chimpanzee ' Family HOEEHIIAE ; ; Genus; HOMO ' . Goimaon name = Han A ll of . the abore non-husian primateSj, with, exception of the rhesuss were obtained from zoological gardens by the Department of

Anthropology of the University of Arizona© The rhesus monkey was obtained from a biological supply house© Although not one of the non­ human primates came directly from a native habitat9 they a ll seemed

to be of normal development and showed no evidence of rachitic develop­ ment or any other growth d eficien cies» The rhesus monkey used was a male adult-with .permanent dentition fully erupted and epiphyses fully closed© . The total length of the . humerus in this specimen was I606 cmso It possessed twelve ribs and the tip of the inferior angle of the scapula was at about the level of the cranial border - of the seventh rib©

The baboon was a young adult female with permanent dentition^ and the epiphyses at both the proximal and distal ends of the humerus and clavicle fu lly closed© The humeral length was 15 o 8 ems© There were twelve ribs in this specimen with the tip of the inferior angle of the scapula extending caudalward to about the le v e l of the caudal border of 'toe .serentte aSW v'- f .. I-- ^ / ^■; 'i ;;; v:- "':: v . ' / . - The gibbon was aa adult female mth complete epiphyseal, union at both ends of the humerus and clavicle^ The humeral length was 22„h ems^, " %ere'$were thirteen ribs and the tip of the inf erior angle of the ’ scapula reached to the;cranial border of the ninth ribo . ; , ’ - •.: . V , The chimpanzee specimen was that of a young ruale with an. estimated . age of five years based on tooth eruption schedules (Schultzs 19h0)f ; ■. The epiphyses, at the distal' and proximal ends of the humerus were not

completely fused-, although both epiphyses of the cla v icle were com- p letely joined^ The humeral length' was 19o5 cms« The animal possessed ; twelye ribs .and the tip of the inferior angle of the scapula was at the level-"of fhe:--middle of the ' sixth ribe ’ " v - -d :. : 1 --;:

. ■ Only the left side of the shoulder girdle was dissected in each ' : of the forms0 Before actual' dissection was started<> preliminary topo­

graphical relationships were noted® These included such observations '. i as direction of the clavicle and position of the scapulas .level of the ;; inferior angle Of the scapula upon the ribs-, -arid relatiye -distances ' betoeen the .iliac crest and the last ribs '1 ' x'- 'i' ^' ’ v' di:. - :r

. . After the skin arid superficial fascia had been removed-, the out­ lines of .the extrinsic muscles of the ventral and dorsal shoulder - were

■ cleaned up and a photograph was taken*' Detailed notes were-made of th ei

v X •: - v : : X- V i'-- ’'x.-'.X'"'-- ■ X ;■ V .- -X.Xx form and position of each musclee The width of the origin and insertion was measured with sliding calipers in those .instances when such measure­ ments: were- thought, to ' be> f hc^arifly@; or .descriptive value* In

.addition^ the origin and insertion Were described with reference to ; ■.... ' : ' ' ' established anatomioaX landmarks» {;:% .i;;. Because of the intimate relationship between the nerve .supply, and' : the inuscles details of innervation were observed as fully as possible*'. An effort was made. to trace each nerve back, from the muscle. t;o its derivation from the brachial plexuss or in the case of the m0 -trapeziuss - back to' the exit of the nerve between the long muscles of the necko The relationships of the v&rious components of the brachial .plexus were ob=': served in the animal^ then the plexus; was;dissected out as far as the foramina of ex it of the spinal nerves; upon removal i t was pinned to a board in order to facilitate the sketching of this structure, " The sketches upon which the drawings of muscles in this report are based?:’were made before the removal of any of the muscles» • To fa c ilita te comparisons between the different animals,, the thorax5 as . illustrated^' has been reduced to Ihe .same total length in each animalB;

Because of the great similarities in the musculature of the. rhesus and the baboon, only the latter is illustrated,, Some drawings' of the musculature, of the rhesus can, be found in The Anatomy of the' Rhesus. Monkey by Hartman and Straus (1933)° \ . . - /'y; 1 After sketches and notes were completed^ all the muscles were re- . moved from the- shoulder, and. the bones were cleaned of a l l adhering muscle. tissue o The comparative osteology, therefore, is based on the actual specimen dissected, in a ll cases except that of thechimpanzeeand man0 ' Because the epiphyses were not joined in the chimpanzee, i t was decided to utilize the bones of an adult chimpanzee. for these comparisons®-

Notes on the locomotor habits of the non-human primates are taken entirely from the literature, none is based on personal.'observations® ■ ' Chapter Three ' - Descriptive Hyolegy of the Pectoral Girdle . The following chapter presents detailed descriptions of the musculature of the left pectoral girdle and upper arm of the baboons gibbon and chimpanzees A detailed volume on the anatomy of the rhesus is available which is based on many more specimens than in the present caseo Therefore^ the musculature of th is form is not included in this chapter (Howell and Straus'^ 1933 $ 89=173)* Bveiy muscle is described in full for each animal at the risk of redundancy* This type of presentation should be useful in segregating the descriptive findings from the comparative statements* It is hoped that presentation of. these details will be of aid in the establishment of the range of variation which can be expected for anyone species*. The order in which the following muscles are arranged is the same as that in Gray8 s Anatomy*, twenty-fifth edition^, with a few modi­ fications* There are other schematic plans based on functional groups of muscless muscles with common innervation^ or those derived from the same embryological muscle plate which also might have been useds but the widespread use of the topographical scheme in the literature of anatomy dictates the presentation in the following manner*

M* trapezius (KLates 2 and 8) . Baboon,

Forms flat, triangular, broad* Positions a single sheet of .. M= trapezius (conto) . ' ' ■ J. : : 16 muscleon the upper back and dorsal cervical•region just beneath the

Skin0 Origin; fleshy from the occipital protuberance and laterally / r. along' the superior, nudihl lin e foi*; a distance of 1«3 cms.S5 fr^om the : cervical midline and the spinous processes of the seventh cervical to the eleventh thoracic.vertebrae0. The part of the origin from the : d d d / d , , pi . p :,py: i- : ' rapinous process of. the eleyehth thoracic vertebra is by means of a , .shoni> triangular aponuerOsis<, . The fib ers of the muscle meet across :. -. the midline except for a triangular aponuerosis vi ich extends from the : ’ spine.of the' seventh ceivical down to the second thoracic. vertebra0 ' . The portion from the occipital origin and the cervical region is : , '

/ entirely separable from the r est of the '.muscle® The.most caudal origin ; of the muscle overlaps the cranial origin of mc.latissinus dorsi for ■: 3« 8 - cmso s or from the - le v e l.of the eighth to the level, of the eleventh : thoracic vertebra0: Insertions the portion from the occipital, and ; . •’ - cervical regions passes laterally caudalmrd. and ventrally to insert : v : ■■ upon ths medial border of the acromion and the lateral one-fourth of

the Clavicle for :a 'distance of 2o3 cms0 This insertion is' entirely ; . .. fleshy® The portion of the muscle arising from the upper thoracic spines :passes, almost directly lateralward to. insert upon the cranial border of ■ .c / .. . \ v ' p p .•■p ..v - the. scapula spine for its entire length by .means of a thin aponuerbsis■ d : medial]^ ahdvfleshy fibers laterally# The portion insert,ing at the - root of the scapula spine does so by. means of a stout tendon® The most 6audal .dibers-pass obliquely cranialward and laterally to insert upon ' '

: the caMal\ border of t # seapula and upon the posterior deltoid fascia® The approximate greatest extent of this insertion upon the seapula spine X? Mo trapezius (conto) was 3o0 ciaso inmerTations a , accessorius and branches from 03 and ciio ■. ■ ■■ ■ :

Gibbons

Foms thin5 flats triangulars broad® Thickest in the cervical region® Positions superficial on the upper dorsal thorax and cervical

regions Covers the medial .portion of the scapulas cephalad to the

scapular spineo Origin? the muscle arises as. a continuouss indivisible sheeto The most cranial point of origin does not extend up to the occipital protuberances but begins from the cervical midline at a point 2®3 cmso from the occiputs or about at the level of the 3rd cervical vertebrae The origin extends from this point down to the spinous process of the. thirteenth thoracic vertebras overlapping the superior origin of the m® latissimus dorsio The origin from the tenth to thirteenth

thoracic spines is aponuerotieo There is also a narrows triangular aponuerosis between the second and seventh thoracic spines® Insertion? the fibers from the cervical region pass obliquely downward and lateral" ward to insert upon the lateral half of the clavicle for a distance of 3o8 cmso The fibers from the upper thoracic region insert on the medial

border of the acromion® The fibers from the lower thoracic region pass obliquely cranialward and lateralward to insert upon the caudal border of the scapula spine for a distance of 3°h ems® Innervation? n0 accessorius and branches from 03 and GI4.®

Chimpanzees

Forms flats triangular^ broad.® Positions superficial on the ■ . ' .. • 18

Mo trapealtts (ooato) upper dorsal tBiorax azid eezirlcal region^ The muscle is thickest in the crease of the neck0 Origins from the inner third of the superior nuchal line for a distance of 2*3 cms®9 from the occipital protuberances, from the cervical midlihe and from, the spinous processes of the sixth

cervical down to the tenth thoracic vertebrao The fibers of the muscle meet across the midline for the .fu ll extent of the muscleo Insertions the fibers from the occipital Origin and from the cervical midline down to the level of the second m- third thoracic vertebra pass obliquely downward and laterally to insert upon the outer half of the clavicle for a distance of 3°5> cmso The fibers from the middle thoracic vertebrae insert upon the acromial process* The fibers from the lower thoracic vertebrae pass obliquely upward and laterally to insert upon the fascia covering the spinal portion of the m0 deltoideus

and along the spine of • the scapula® Innervations n® accessor ins and branches from 03 and Git®

Mo latissimus dorsi (Plates 3, %3 and 9) Baboon

- Forms flat/ triangular^ thin® Positions upon the posterior and lateral thorax^ passing over the posterior axillary border0 The cranial border of the muscle covers the inferior angle of the scapula for a few cmso Origins fleshys from the spinous processes of the eighth and

ninth thoracic vertebrae, and from the lumbodorsal fascia down to about the level of the sixth lumbar vertebra* There is no.origin from the iliac eresto The most lateral caudal fibers extend about two-thirds of Mo latissiiaus dorsi (conto) the distance between the twelfth rib and the iliac crest@ There is no interdigitation with the fibers of the m<> external oblique abdominis o Insertions the muscle fibers converge as they pass eranialward and

lateralward5 the muscle becoming thickest in the axillary regime They

Insert by means of a long (3oh cmso), narrow (loll. cmso)5 f la t tendon . upon the posterior border of the intertubercular groove of the humerus^ slightly distal to the insertion of the mo teres zmjoro Innervations . . n<, thoraeodorsaliss G8 and Tl*

Gibbong _ . . Forms' thin, flat, triangular, thickest in the axillary region before forming a tendon of insertion„ Positions upon the posterior and lateral thorax, passing over the posterior axillary border* The cranial border of the muscle covers the inferior angle of the scapula for a few centimeters^ Origins by a thin, triangular aponuerosis ' from the spinous processes of the seventh to ninth thoracic vertebrae, • fleshy from the spinous, processes of the tenth to thirteenth thoracic

and the first lumbar vertebrae, from1the lumbodorsal fascia, and by fleshy slips from ninth to thirteenth ribs, interdigitating with the . origin of m0 external oblique abdominis» There was no direct origin

from the iliac crest® The caudal border of the muscle extended to a point approximately half way between the thirteenth rib and the iliac

cresto Insertion: the fibers converge as they pass eranialward and lateralward to their insertion upon the posterior border of the inter- . tubercular groove of the humerus« Insertion is by means of a broad. - • ; . ' .. : . ■ ■ , . , 20 M».latissinms dorsi (cont6) ' flat tendons l e9 c»s* longs for a distance of 206 cmsa.along the humeruss The insertion of m0 teres major fuses with the tendon of insertion proxiraallys and the m<, dorsoepitroehlearis takes its origin from the tendon distallyo Innervation? n0 thoracodorsalis5 08 and Tl0

Chimpanzee Forms thins flats triangular* Thickest in the axilla just before forming a tendon of insertion* Positions superficial on the lower portion of the back and the lateral thoracic wall* The cranial border of the muscle passes orer the inferior angle o0 ems* from the anterior superior spine of the iliumo Total width of ilium, anterior superior spine along the crest to the posterior superior spine is 7

latisslraus dorsi (cpnto) intertubereular groove of the humerus for a distance of 108 emso This insertion is just lateral and slightly distal to the insertion of the ztio teres majoro The Bo dorsoepitrochlearis arises from the tendon of

insertion of the m6 latissimus dorsi distallyo dhnenrations -_n» thoracodorsaliSj, G8 and Tlo '

M» rhomboideus (Plate 9) Baboons Forms composed of three distinct slips3 each of which is flat and quadrangularo Positions upon the upper back between the vertebral ; column and the scapula^ covered above by the m0 trapezius0 Origins Pars capitis - this is a slender slip which arises from the superior nuchal-

line for a distance of 2<,7 cms« lateral to the occipital protuberance^, from the occipital protuberance and from the cervical midlineo The origin is covered by that of me trapezius mediallyQ Pars cervicis - arises from the cervical midline below the pars capitis 5 and from the spinous processes of the sixth cervical down to the second thoracic vertebra* The most caudal border of this portion is overlapped by the

cranial margin of the pars thoraciso Pars thoracis - arises.from the spinous processes of the third to the seventh thoracic vertebra and the interspinous ligaments* The pars cervicis is the widest portion of

the muscles Insertions Pars capitis - inserts by means of a very short5 slight tendon upon the vertebral border of the scapula for a distance of h mm0 between the insertion of the m„ levator scapulae and the pars cervicis» Pars cervicis ~ inserts by means of a broad aponuerosis upon the vertebral border of the scapulas starting at a 22

M0 rhomboideus (conts) point io3 cfflSo cranial to the root of the scapula spine and continuing caudally for 2,8 cmso from;this point0 Pars thoracis - inserts by- means of fleshy fibers onto the caudal half of the vertebral border of the scapula down to the inferior angle® All fibers overlap the border somewhat to insert upon the fibers of insertion of the m* sefratus anterior® Innervations a ll three portions receive branches, from n® dorsalis scapulaes (Cli) G5<>

Gibbon^ -iic-n.; n _

0#omj[Plate:9) ' ' Forms thin.^ f l a t s quadrangular® Positions on the upper baeks covered by the m® trapezius® Origins fleshy from the spinous processes of the seventh cervical dotm to the sixth thoracic vertebra* The uppermost origin was Just slightly aponuerotic* Insertions along the vertebral border of the scapula down to the inferior angle for a distance of i|.06 cms* Innervations n0 dorsalis scapulae^ 05*

Mnor .(Plate--^):" ; Forms fla ts oblong quadrangulara Positions on the upper backs covered by m® trapezius* The inferior margin overlies the superior margin of m« rhomboideus major* Origins from the spinous processes of the sixth and seventh cervical vertebrae s and the interspinous ligaments by means of a thin aponuerosis* Insertion; upon the vertebral border of the scapulas beginning l„k cms® below the medial angle for a distance of 6 mm» The insertion i s separated from that of m® rhomboideus major • by the inferior insertion of the m$ levator scapulae* Innervations . ... 23 Mo. rhoaboideus minor (conto) a. dorsalis scapulaes 03®

Mo rhoaboideus (Plate 9) Ghimpanzeej, . Forms thick, quadrangular® Positions on the upper back between the vertebral border of the scapula and the vertebral column0 Covered dorsally by the a® trapezius and bounded cranially by the mo levator scapulae® Origins th e.rhomboideus i s not d ivisib le into two parts as in man® It arises by means of a very thin aponuerosis from the dorsal midline as high as the level of the fourth cervical vertebra, and from the spinous processes of the sixth cervical down to the fourth thoracic vertebra® The to ta l length of the origin was 9*5 cms® Insertions was upon the vertebral border of the scapula beginning about 2®5 cms® below the medial angle and continuing to the Inferior angle® Innervations m® dorsalis scapulae, (Gli), C5o

M0 levator scapulae (m» atlantoscapularis posterior) (Elate 9) Baboon, / / ■ '

Forms two thin, slender slips® Positions on the lateral surface of the neck, covered above by the me cleidomastoid and below by the m® trapezius® Origins by two fleshy slips from the dorsal surface of the transverse processes of the first and second cervical vertebrae® Inser­ tions the muscle continues as two thin, flattened slips to insert separately upon the medial angle and vertebral margin, of the scapula by means of a thin aponuerosis® Innervations branch from Cite Me levator scapulae (cont0) ■ Gibbo% Fomt three distincts slender<, flattened slipso Positions on the lateral surface of the necko Runs deep to9 and is almost entirely covered by the m, trapezius,. Origins from the transverse processes of the second to fourth cervical vertebrae« Insertions is upon the medial angle and around to the vertebral border of the scapula 0 The slip from the second cervical vertebra inserted separately into the - vertebral border of the scapula and the supraspinous fas:ela0 Innerva­ tions 03 and Clio •

. Chimpanzee? - Forms four flattened, slightly oblong slips* Positions on the lateral surface of the neck, covered dorsally by the mc trapezius and the iru cleidomastoido Origins this muscle was composed of four distihet parts which arose from the transverse processes of the f ir s t through the fourth cervical vertebrae» The most cranial portion was the largest, each slip being increasingly smaller» The:slip from the fourth cervical,

vertebrat was very small but distinct* Insertion: the slips inserted along the vertebral border of the medial angle for a distance of 3,2 cmso The caudal border of the muscle was slightly overlapped by the m* rhomboldeus, but the origin of each muscle was distinct* The slip s from the second and third cervical vertebrae fused just before insertion. The portion arising from the first cervical vertebra inserted separately

just dorsal and cranial to the insertion of the slips from the second and third cervical vertebrae* The slip from the fourth cervical inserted 25 Ho levator scapulae (cont*) separately^ slightly Tentral to the insertion of the previous slips*, Innervations branches from 03 and Clio

Ho omocervicalis (mo atlantoscapnlaris anterior) (Plate 9)

Baboon, ' Forms flat, thin, oblongs Positions on the lateral surface of the neck, partially covered by ms trapezius# Origins from the anterior and lateral surface of the transverse process of the first cervical vertebra# Insertions the fibers diverge slightly from their point of origin to insert deep to the insertion of mi trapezius upon the medial cranial border of the acromial process and the scapula spine for a distance of' 2#2 cms# -Innervations branches from 03 and

Gibbon, - / . •' .

Forms long, thin, flattened# Positions on the lateral surface of the neck and superior aspect of the shoulder, runs deep to the m» cleidomastoid and is covered by m# trapezius# Origins from the trans­ verse process of the first cervical vertebra by fleshy fibers# In­ sertions upon the lateral end of the clavicle for a distance of 5 mm*

The most lateral point of insertion was l<>2 cmso from the acromio­ clavicular joint# Innervations G3 and Gli.#

Chimpanzee,

Hot observedfor a description of this muscle see Stewart (1936s lk9b 2 #

. ■ :f jH<, pec*©ralis major (Plates 13 2a lta n d 6) ; ;V. " v- .

^ Baboon#: _ ' : : , ^ ■ ; /V-:. v; ; ' ^" j . Forms ’broadj flat5 triangulars thickest in the axillary region® Positions on the upper ventral;thorax lateral to the midline. Origins t;:'- the muscle is divisible:: into two parts^ capsular and eostosternal» • The pars capsularis arises thickly frorn the sternoclavicular joint and the: - body of the manubrium for a distance of lo^cmso I t i s separated from the clavicular origin of deltoideus by 1*6 cmsa The pars costo- ; sternalis arises from the midline for the entire length of the sternum •

and from the costal cartilage of the- eighth rib for a distance of 1<,5 cms« • lateral to the midline o The fibers of both portions meet across the

midlineo Insertions is complex^ the caudal fibers of the pars costo= ; ■ - •

. . ' ' ■ ■ ' - sternalis are.successively folded under beneath the lower margin of the ; muscle sheet arid insert separately with the tendinous sheet of insertion ? ' •; of the m0 pectoral i s abdominalis {along the proximal end of the humerus 5 ;: ; medial to. the insertion•of the rest of.the pectorails sheet» The re- raaining portion of the pars cestosternalis and all of the pars capsularis forms a broad; thins tendinous sheet which inserts, upon the crest of

the major tubercle of the humerus for a distance of 4*2- cms0. Ilong the ' superion-border and deeps- the pars capsularis is fused with the anterior '

border of the m* deltoideus to a variable degree^ Innervation s hn 0 ; thoracales anteriores, .(04), 02, 06, p?, . 08 and ,Tle .

*. „ ■ » ■■ ^ | i ■' *' _ 1 " ■i-r ■„ - . ■ Forms broad, f la t , fan~shapedo . Thickest in- the axilla* Positions on the "Upper thorax, lateral to: the. midiine, ■ bounded along its superior -

-margin: to nu., deltoid* : Origins this muscle was not. separable, into " ■ ' 27 M0 pectoralis major (conto) ■ parts except at the extreme origin where it was partially divisible into abdominals costosternal and elavicular portionso The abdominal portion arose by a distinct slips 2oh cms= wide from the tips of the eighth, and ninth ribs and their costal cartilages® The sternocostal, portion arose from the costal cartilages of the fifth to eighth ribs and from the la tera l margin of the sternum up to a point 1*1 erne* from the jugular notch® The clavicular portion arose from the ventral and inferior border of the clavicle for a distance of 5»2 cms® lateral to the sternoclavicular joint® There was a distinct separation at the midline of the muscles of the two sides5 amounting to 1®6 cms® at the level of the fourth rib and 8 ram® at the level of the second rib® Insertions the insertion was complex* the fibers from the clavicle remained superficial^ the lower fibers twisted toward th eir insertion ■ passing deep to the more cranial fibers® The main attachment was upon the crest of. the major tubercle of the humerus for a distance of 6=1 cms® by means of a strong tendon® This tendon was fused laterally with that of the m= deltoideus® The tendon split to send a leaf over the tendon of the long head of m= biceps to insert along with the tendinous origin of the short head of the m®' biceps for a distance of 1*9 cms®

This latter tendon was not as heavy as that inserting with the deltoid^ but was relatively strong® The most inferior point of insertion was 9*5 cms® from the proximal end of the humerus® Innervations mn® thoracales anterioreSs 05 to Tl®

Chimpanzee,

Forms broad, flat, triangular, thickest in the axillary region® 28 Mo pectoralis major (conto)

Positions superficial on the upper ventral- thorax, lateral to the mid<= lineo Origins this muscle was clearly divisible into three parts according to origin, am abdominal,- a costesternal, and a clavicular portion* The pars abdominis arose from the cranial border and ventral surface of the fourth to the seventh ribs and from the sheath of the m<, external oblique abdominis« The most lateral origin from'the seventh rib was by a. separate fleshy slip 2„2 cms* wide and 2<>5 cmso long* The pars costostemalis arose from the fourth rib and costal cartilage as well as the whole length of the sternum up to a point 2o0 cms* from the sternoclavicular joint* The pars clavieularis arose from the inferior border of the-clavicle, lateral.to the origin to m* sternomastoid and along the clavicle for a distance of 5*0 cms* The muscle fibers meet across the midline in the sternal region* Insertions the fibers from the abdominal portion pass obliquely upward and tw ist in the axillary region to pass deep to the fibers from the costosternal and clavicular

origins* The fibers from the. clavicular portion remain superficial* The insertion was by means of a broad, flat, tendon 3=5 cms* long, onto the. crest of the major tubercle of the humerus * Innervations rai* thoracales anteriores, C5 to Tl0

M» pectoralis minor (Elate 7) Baboon,

Forms long, thin, flattened, fan-shaped* Positions upon the ventral wall of the thorax, lateral to the midline> Origins fleshy, from the lateral margin of the sternum starting at a point 20it cms* from 2$

Mo pectoralis minor (coata) . . the sternodlavicular joint and extending for 7<>1 eraso caudally5 and from the costal cartilages of the fourth through sixth ribs« Insertions try means of a stout tendon I 06 cms0 wide upon the coracoid process of the scapulaj, the coracoacromial ligaments and the capsule of the shoulder

joint* Innervations branch of mu thoracales anteriores3 (Gh)3 0$ to flo ■ ■■■■■ ■" ■ ' ' : '

"Gibbon, Forms long, narrow, ovoid, with a long tendon of insertion* Positions on the upper ventral thorax, lateral to the costal cartilages, completely covered by the m* pectoralis major* Origins fleshy from the

second to the fourth ribs, and by a thin aponuerosis from the fifth rib*. Insertions was tendinous upon the coracoid process of the scapula and upon the coracoacromial ligament* Innervations branch of the nn*

thoracales^ anteribres, C5> to Tl0

Chimpanzee, Forms long, thin, triangular, with a long tendon of insertion*

Positions' upon the upper, ventral thorax, lateral to the midline, covered ventrally by the m* pectoralis major* Origins by fleshy fibers from

the ventral surfaces of the second through the fourth ribs* Width of origin was as followss from the second rib 1*8 emsj from the third rib ,1*8 cms| from the fourth rib 2*0 ems* ' Insertions was by means of a long, thin tendon upon the capsule of the shoulder joint near the coracoid process of the scapula* Innervations a branch of nn* thoracales anteriores, 05 to Tl* • ' 30 Mo pectoralis abdomiaalis

Baboon^ Forms loag? 'thin, fan«=shaped» Positions on the lateral border of the ventral thorax®. The medial border of. the muscle is bounded near its origin by the caudal fibers of m» pectoralis major® Origins fleshy,

from the sheath of the m® external oblique abdominis for a width of

•4*7 emso The origin is completely caudal to the costal cartilages framing the abdominal cavity® Insertions . the fibers pass cranially and la tera lly to insert upon the upper oms* of the humerus by means of a broad, thin aponuerosis, in common with the caudal portion of the m® pectoralis major* The pectoralis major is thus fused with the m®

deltoid insertion laterally and with the tendon of.insertion of the Bo pectoralis abdominalis medially® The insertion of the m® pectoralis abdominalis extends up to the coracoid process and joint capsule, but

passes deep to the insertion of the m® pectoralis minor = Innervations; a branch of nn® thoraeales anteriores, CJ? to Tie,

M0 subclavius (Plate 7) ■ ' : Baboon, ^

• Forms narrow, elongated, flattened cylinder« Positions on

the upper ventral thorax, between the clavicle and the first rib, covered ventrallyby the m® pectoralis major® Origins fleshy, from the caudal • ; ventral border of the first costal cartilage for a width of 7 mm® Insertions the fibers run laterally and obliquely upward to insert upon the caudal border of the middle three-fifths of the clavicle for'

a distance of 3=3 cms®, reaching a point 1®2 cms® from the acromioelavicular , V ■■ :■■■ ■ - 31 M«, subclavims (coni*) • jointo Innervations n» subclavius^ (Oh)s G60

Gibbon., - , 7::' '■ Forms shorts thins flattened cylindrical^ Positions on the

upper "ventral thoraxs between the clavicle and the f ir s t rib , covered ventrally by the a« pectordlis major* Origins by means of a. long, flat tendon.from the second costal cartilageo The width of the origin is iol cms* and the length of the lateral margin of the tendon is 2*1 cms* Insertions upon the dorsal, inferior border of the lateral end of. the clavicle for a distance .of 2*9 reaching a point 1*8 cms® from

the acromioclavicular joint« Innervations n* stibclavius, 05 and G60

.Chimpanzee, Forms short, narrow, slightly flattened cylinder0 Positions on

the ventral thorax, between the clavicle and the first rib* Covered ventrally by the clavicle and m» pectoralis major* Origins by means of a short, slender tendon from the first costal cartilage just lateral to the costoclavicular ligament* Insertions upon the inferior surface of the clavicle for a distance of 2.1 cms* reaching a point 2*0 cms* from the acromial end* Innervations n* subelavius, (&}.), G$ and 06*

H* serratus anterior (Plates 1| and 7) Baboon, ' . •

Forms broad, flat, fan-shaped,, serrated* Positions on the lateral and posterior thoracic wall, covered dorsally by the m* latissimus dorsi and the scapula' and its associated muscles, covered ventrally by 32

Me serraius anterior (conts) the m0 pectoralis major0 Origins pars cervicalis3 arises from the transverse process of the third to the seventh cervical vertebraeo The pars thoracalis arises from the caudal borders of the first to the ninth ribs by fleshy digitations$ The origin from the last five ribs interdigitates with the origin of m* external oblique abdominis <, The points of digitation become increasingly more dorsal in position as they proceed eaudallyo The cervical and thoracic portions are separable for their entire extent* Insertion; the fibers converge towards .insertions the muscle being thicker near its attachment* The cervical portion inserts along the ventral margin of the vertebral border of the scapula for 2*2 cms® from just below the medial angle to the scapula spineo The thoracic part inserts along the remaining caudal portion of the vertebral borders beginning at about the level of the root of the scapula spine and continuing down to the inferior angleQ The insertion at the inferior angle is more tendinous than that of the rest of the muscle* Innervations na thoracalis longus| Cj? to 08, also a branch from Bo dorsalis scapulae to the cervical portions (Olt),

Gibbon9 . . .

Form; thins flats fan-shaped, serrated* Position; on the lateral and posterior thoracic walls covered dorsally by the m* latissimus dorsi and the scapula and its associated muscless covered ventrally by the m0 pectoralis major0 Origins by fleshy digitations from, the first to the thirti@ithbribs5‘heTteibMg£ht"'frbi^the^t8lrtetethsribi#S"§d^bsSdr@f three separate digitationss the most dorsal extension being about 3 cms* ' ■ ; - ' 33 M0 serrates anterior (conto) posterior to the mid-axillaiy line» ■ From the sixth to the thirteenth;:-rib the origin interdigitates iclth that of m« external oblique abdominiso

The slips from the first and second ribs are clearly separable from the rest of the muscle for their full extent0 Insertions upon the ventral surface of the vertebral border and inferior angle of the / scapula for a distance of 3o0 cms0

Ghimpanzeej Forms; flat, fan-shaped, serrated* Positions on the Enteral and posterior wall of the thoraxo Covered dorsally by the mo latissimus dorsi, and the scapula with its associated muscles, cqVered ventrally by the mo pectoralis major0. Origins from the cranial and ventral margins of the tips of the ends of the first to the twelfth ribs0 From . the fifth.to the ninth rib the. origin interdigitates with the origin of m0 external oblique abdominiso The origin from the f ir s t and second ribs is quite short and thick and is partially separable from the rest of the muscleo There are two digitalions.arising from the twelfth rib, one posterior to the other0 Insertions fibers from the most caudal origin pass almost vertically upward to insert upon the ventral surface of- the inferior angle of the scapula <, The more cranial fibers run increas­ ingly obliquely caudalward and posteriorly to insert upon the ventral margin of the vertebral border of the seapula0 The fibers from the first two ribs insert upon the ventral surface of the medial angle of the scapula® Innervations contributions from Og to first two digitations, n® thoraealis longus, C3, 06 and 07* 3k Mo deltoideus (Plates 1, 2, 3S W 5S 6 and 8) Baboon5 ' ■ Toms thins flats trianguXars with three heads of origin. Positions on the lateral shonldeiy rentral5 superiors and dorsal aspects^ and the medial aspect of the upper arm* Origins the muscle is separable into parts on the basis of origins ever, though each part is not d iv isib le for its entire extent» Pars claviculariss arises from the ventral border of the clavicle, for a distance of c* h cmso mediallys beginning lo7 caso medial to the acromioclavicular joint0 A distinct triangular space is formed by the dorsal border of* the pars claviculariss the edge of the clavicle and the ventral border of the pars acromialiso Pars ' acromialiss arises from the lateral and cranial: surfaces of the acromial • r ' - ' , , process of the scapula and the caudal border of the scapula spine for a distance of 2oh cmso Pars spinaliss arises from the caudal border - of the scapula spine for a distance of 5o2 cms« The lateral 109 cms0 is flesh yth e remainder is by means of an aponuerosis of varying lengtho The spinal portion does not extend to the vertebral border of the inferior angleo Insertions the spinal portion is separate for almost its entire length, then it joins with the other two parts to insert fleshily upon the entire deltoid crest of the humerus<, The inferior point of origin is 7o5 cms« from the head of the humerus,, being fused with the uppermost fibers of origin of the mffl brachialiso The pars clavicu- laris deltoideus inserts laterally with the nu pectoralis major along the crest of the minor tubercle® Innervations n0 axillariss G$s G6 and

_ '■ Gibbon^ '" •

Forms long, triangular,. crescent shaped in sectionc Positions 35 M0 deltoldems (conto) upon the lateral shoulder and upper arm5 down over the infraspinous muscle to the inferior amgleo Origins the muscular sheet was divisable into two portions^ the antereosuperior portion and the infraspinous portiono fhe pars antereosuperioris arose from the lateral 203 cmso of the clavicles the acromions and the scapula spine to within 1»3 cmso of the root of the. spineo The pars infraspinatus arose from the fascia infraspinata all the way to the vertebral border and inferior angle of the scapulao This portion was separable from the main mass' of the muscle for at least half the distance to the insertion^ The belly of the portion arising from the acromion was covered su p erficially by an aponuerosis for a distance of 8aG cmso distally from the lateral border of the acromion*, This aponuerd sis was roughly triangular in shape 2 the base of the triangle being along the acromion. Insertions the fibers converge to insert upon the humerus by means of fleshy fibers and tendinous bands. Medially the insertion is blended with that of the m. pectoralis major, Distally the insertion is blended with the origin of the., m,brachialis, The most distal point of insertion is about

12 cmso from the head of the humerus0 Innervations n* a x illa r isj • 06 and 07*

Chimpanzeeg

Forms thin, triangular, crescent shaped in section. Positions superficial, on the ventral and lateral aspects of the shoulder, enveloping the shoulder capsule. The major portion of the muscle is on the lateral portion of the shoulder. Origins fleshy, from the ventral ; ' V " : ' - ■ "V ^ ■ ■ f' 36 H0 deltoideus (conti) border of the lateral 2j.o0 maso of the clavicles from the lateral border of the acromion and the caudal border of the scapula spine for a distance of 8*3 ctos0 At the point where the scapula becomes thin .and • knife-like5 the origin becomes tendinous with the fascia infraspinata* insertion? the fibers run obliquely upward and lateralwards then con- ■ ■verge downwards to insert approximately 7*3 eras, from the proximal end of the humerus on the lateral surface of the humerus® The insertion is partially blended with the origin of m0 brachialiso innervations ho a x illa r is5 C5S G6 and C7o

; M® teres minor (Plate 10) Baboon^ • Forms long5 thins wedge shaped in section^ flattened laterally0 Positions oh the axillary margin of the scapulas covered by the pars spinalis of the m® deltoideus0 Origins from the axillazy border of

the scapula separated from the m® teres major by the long head of the m* tricepso Width of origin is 3*1 cms.. Insertions is upon the distal part of the greater tuberosity of the humerus by means of a

tendon 9 mm® wide 0 Some of the fibers pass over above to insert upon the capsule of the shoulder joint,, along with the fibers of m0 infra- spihatuso Innervations n6 axillariss (6U)» 06 andG?*

Gibbotis

:; Forms shorts thicks oblong® Positions , on the lateral border of the axilla5 bounded medially by the m0 infraspinatus, covered aboveby ■ ' . ; ' ■ , . . 37 He teres minor (conto) • the Mo deltoideu.s0 Origins - from the axillary border of the scapula by fleshy fibers for a distaftce of 3=2 cmso caudally from the inferior border of the glenoid cavityo Anteriorly and superiorly the origin is slightly fused with the origin of the long head of the m0 trieepso Insertions the fibers diverge from the origin to insert widely upon the crest of the major tubercle of the humerus by fleshy fiberse Proximally some fibers pass over to insert upon the capsule of the shoulder joint> Innervations m0 axillarisj, G5S 66 and 07<, •

Chimpanzee g . . Forms thicks oblongs triangular in section® Positions on the axillary border of the scapulag hounded superiorly by the infraspinatuss interiorly by the long head of the m* tricepsg and covered above by the spinous portion of m® deltoideus» Origins along the axillary margin of the scapula for a distance of hoO cms0 from the inferior margin of the glenoid cavity» Insertiong the fibers converge from their origin to form a very short tendon which inserts on the distal border of the major tubercle of the humerus<, Some of the superficial fibers pass over the tendon to insert into the capsule of the joint* Innervations n0 axillarisg C^g G6 and Q7*

Mo teres major, (Plate ip) Baboong. r

Forms thing flatg ovoid® Positions on the axillary border of the scapulag and covering the inferior angle* Origins the muscle arises Mb teres major (conto) . widely from the fascia infraspinata and. curves around the asdllary :

border to take some of its origin from, the subscapular fasciae The muscle also arises from the axillary border of the scapula for emso-p from the inferior angle and along the vertebral margin for 105 eras® There i s a d istin ct process oh the axillary margin from which the muscle takes its major origin; this fossa is separated from the infra™ spinous fossa by a ridge* Insertions the fibers converge as they pass craniaUy and la ter a lly passing deep to the long head of m® triceps; towards insertion the tendon passes deep to the a.® coracobraehialis medius and the tendon of insertion of latissim us dorsi® The in­

sertion is 9 howevers completely separate from that of ra0 latissimus dorsio The wide flat tendon of ra® teres major inserts upon the crest of the minor tubercle of the humerus for a distance of 201|. eras® dis= talward from the surgical neck of the humerus® At the proximal point of insertion i t is deep to m0 coracobraehialis profundus for a few mm® This latter muscle inserts slightly upon the tendon of m® teres

major® Innervations n<, "teres.major* .((%),,. :G6 and -0?»

Gibbons

Forms thiekp long, rectanguloid* Positions on the lateral border of the axilla? bounded medially by the m® infraspinatus9 covered inferiprly by the cranial border of th e latissim us dorsi® Origins

by fleshy fibers from the .axillary border of the scapula for a distance of 3®3 eras® from the inferior angle and by means of a very slight \

aponuerosis from the inferior, angle® Insertions the fibers diverge - 39 • Mo teres major (cents) from their origin, to insert by means of a breads flat tendon in common with the insertion of the su latissimus dorsio Some fleshy fibers also insert anterior to the insertion of m* latissamus dorsi® Innerra.-= tion# n® teres majors 06 and G?#

Chimpanzee^- 'Forms extremely thickr, oblong muscleo Positions on the posterior margin of the a x illa s covered above by the insertion of the long head of the Bio triceps and below by the cranial' border of the latissimus dorsi# Origins from the dorsal surface of the axillary border of the y scapulas from the inferior angle cranially for a distance of bo2 cmso - and from a triangular shaped area on the. inferior la te r a l fascia of the m0 infraspinatus«, Insertions the insertion is separate from that of the mo latissimus dorsi and is hidden by the long head of the m». triceps brachiio The insertion extends for a distance of 3«, 2 cmso along the crest of the minor tubercleo The most proximal point o f insertion i s 5 mmo lower than the most. proximal point of insertion of m* latissimus dorsio The distal insertion is- lo3 ems® lower than the distal point of insertion of m® latissimus dorsi® Innervation? m® teres major5 G$s G6S; and G7a /

Ms supraspinatus (Plate 10) -• Bab©oh3

Foimsthicfcj ovoids with three slips of ohigino Position? occupying the supraspinous fossa® Origins the muscle arises from the • supraspinous fossa and the cranial border of the scapula spine® The distinctness of the three slips of origin is variable® One slip, the Mo siapraspinatixs (conto) pars Inferierls arises from the cranial border of the scapula spine0

It fuses almost immediately with the pars proprius o The pars superioris is more dist±ncts arising from the cephalic border of the scapulas extending medially from the coracoid process along the cranial border for about 3o5 cmso The pars proprius arises from the supra=> spinous fossa proper0 Insertion? the fibers converge laterally^ and as they pass under the coracoacromial ligament^ they become tendinous* The shorts wide tendon inserts upon the most proximal point of the greater tuberosity of the humerus for a width of 1*1}. ems* Innervations n* supraseapularisy (Glt).s C^o

Gibbon^ ■ ' ■.

Forms longj, thing triangular* The long side of the triangle is along the base of the scapula spine® Positions occupying the entire supraspinous fossa., covered dorsally by the m® trapesiuso Origins fleshy from the medial two=thirds of supraspinous fossa and the cranial border of the scapula spine® Insertions the fibers converge as'they pass laterally to insert upon the major*tubercle of the humerus® The

.muscle becomes tendinous just prior to passing beneath the acromial process® Innervations a® suprascapulariss

Ghmpangeeg i - '

Forms f la t 5 'triangulars somewhat wedge shaped in section*

Positions occupying the entire supraspinous fossas covered by the m® . trapesius® Origins- from the medial two-thirds of the supraspinous fossa and cranial border of scapula spine by fleshy fibers® The fibers Mo supra spinatus 9 (conto) run lateralwards converging and passing beneath the acromion process and coraeoacromial ligament® insertions at the la te r a l border of the acromion the fibers become tendinous and attach to the major tubercle of the humerus close to the proximal end® Some fleshy fibers also attach to the capsule of the joint0 The insertion adjoins that of the m0 infraspinatus laterally and extends from there to the intertuber- cular grooveo Innervations ' Be suprascapulariss (Gh)s C5o

Ms infraspinatus (Plate"10) Baboon, : : ’ ' Forms long, thin, triangular« Positions occupying the entire infraspinous fossa, covered medially by the m« trapezius, inferiorly by the Ba latisslmus dor si, and dor sally by the pars spinalis of the Mo deltoids Origins is fleshy, from the entire infraspinous fossa, and the caudal border of the scapula spirne® Insertions the fibers converge la ter a lly to form a thick, narrow (7 mm*), stout tendon of insertion® The inferior edge of the tendon is 3»1 'cos* long* The tendon inserts upon the proximal part of the greater tuberosity of the humerus adjoining the insertion of teres minor<> Some fleshy fibers pass over the tendon of insertion to attach upon the capsule of the shoulder joint„ Innervations n« suprascapularls, (Git), 05®

Gibbon,

Forms long, thin,rectangtiloid0 Positions occupying the entire infraspinous fossa, partially covered below by the a. latisslmus dorsi and above by.the origin of the spinal portion of m* deltoideus® Origins ; Ms Infraspinatus s (conto) fleshy from the medial two-thirds of the infraspinous fossa* The fossa is quite deep superiorly and laterally^ the muscle being relatively

thick just before converging to form the tendon Of insertion* Insertions tendinous upon the crest of the major tubercle of the humeruss just posterior and inferior to the.insertion df m« supraspinatus» Fleshy

fibers also pass over the tendon to insert widely upon the capsule of the joints Innervations no supra scapular is g 0f>o -

Ghimpangeeg Forms oblongs thick j, not bipinnate* Posit ion# in the infra- spinous fossa9 covered by the mo trapezius medially3 the mm. latissiraus dorsi and teres major inferiorly* Origins fleshy from the medial three-fourths of the infraspinous fossa, the caudal border of the scapula spine and from the infraspinous fasciao Insertions by a short; thick tendon,"1*2 cms® wide, upon the superolateral aspect of the greater tubercle Of the humerus between the insertion of ma teres minor and m0 • supraspinatuso Some superficial fibers also insert into the capsule of the joint* . Innervation: n,> suprascapularis, (Glj.),

‘ • : .• ■■ " ' ■ : ' ■ - ' . • ' ■ ' ' Mo subscapularis (Plate 11) Baboon, . • '. '

Forms thin, flat,-multipinnate* Positions on the ventral surface . ^ 1 i ■ . - ; - i. ' of the scapula, and the anterior aspect of the shoulder capsule* Origins from the entire subscapular fossa by fleshy fibers® Insertions the

fibers converge, passing beneath the common coracoid tendon to insert - upon the entire area of the lesser tuberosity of the humerus* Innerva­ tions nn* subscapulares, (Gij.), G5, G6 and 07* ■ . -■/' V ■ ^ ; i 6 sttbscapiilaris (cont®). , Ghimpanzees . Forms , flats triangnlars fan-shapedg ittultipinnate o Positions occupying the whole ventral surface of the scapulae Origins fleshys from the entire subscapula fossas there are three3 more or less distinct bipinnate slips of origin^ ■which are^ however^, mot entirely divisible«

Insertions the fibers converge as they pass obliquely upward and lateralward to insert by means of a short; tendon upon the whole of the minor tubercle of the humeras5 some fleshy fibers pass over above to .insert upon the capsule of the shoulder joint® Innervations nn0 sub- scapulareSs - 05 and C6e . .

$4o cbraeobrachialis profundus (ELate 12) . Baboons . , -

Forms shorts thicks ovoid* Positions on the upper arm.between the surgical neck of the humerus and the coracoid precess0 Origins

from the deep surface of the coracoid tendon of the biceps and fieshily from the coracoid process proper <> Insert ions the fibers pass laterally beneath the short head of the biceps and the coracobraehialis medius muscle to insert upon the surgical neck of the humerus just proximal to

the tendon of insertion of bu teres majors Some of the fibers also insert onto the tendon of mo teres major for a few millimeterse

Innervations $u musculocutaneuss (Ch)5 G$s 06 and G?® '

Mo coracobraehialis medius (P la te,12) • - - Baboon^

Foims long9 thing flattened laterally0 Positions on the proximal Mo coracobraehlalis meditts (cont«) half of the hwerus between, the short head of biceps and the medial head of tricep s» Origins from the coracoid tendon of the short head of the biceps by fleshy fibers 0 Insertions along the medial aspect o f the shaft of the hwerus for a distance of 205 eras® between m<, brachialis and the medial head of bu .tricepso Innervations. n0 musculocntanenSj, (Clf.)5 05s 06 and G7e

Mv coracobrachialis (Plate 12) Gibbon^ Forms long5, narrows f la t s rectangular9 Positions deepj, on the medial proximal aspect of the humeruss between the short head of the m0 biceps anteriorly, and the tendon of insertion of m0 latissimus dorsi posteriorly® Origins by a flat tendon .from the coracoid process of the scapula® Some fibers also arise from the anterior aspect of the joint capsule® Insertions fleshy along the medial aspect of the humerus for ij.®3 ems® The most distal point of insertion is slightly tendinous, and is ems® from the head of the humerus® Insertion i s slightly overlapped by that of m® latissimus dorsi proximally® Innerva tions n® coracobraehialis, C5S C6 and G7o

Chimpanzee, Forms fusiform,, somewhat flattened near its origin where it arises with the short head of m® biceps brachii® Positions in the . axilla, covered in front by the short head of m® biceps and distally by the long head and short head of the biceps combined® It is also partially covered by the insertion of m® pectoralis major in the front ' ' / ' ■ . : ; - '■ : - • . - h$ M0 coracobrachialis (eonto)

and by tbe insertion of mw latissimns dorsis teres major, and sub- - . J - scapularis in the rear> Origins by flesh y fibers from the coracoid processs anterior and inferior to the origin of the short , head of the ;me biceps brachii with which it is partially fused» Insertions fibers pass disfalwards and attach to the ahterioraedial aspect of the humeral shaft for a distance of 3^2 cmso by means of a very short aponuerosis0 : Innervations no musculocutaneus., 05, 06 and G7o

M® biceps brachii (Plate 12) . - Baboon, Forms long, fusiform, with two heads of origin® Positions on the medial surface of the upper arm® Origins short head, arises by : means of a long (396 cms0), stout tendon from the coracoid process of the scapula, for a distance of 6 mm® long head, arises from the supero­ lateral margin of the glenoid fossa by means of a long tendon, which i s .flattened as it passes, through the bicipital groove of the humerus® The tendon of the long head is It.®8 cms® long and 5 mm® wide® Insertions

the two heads are completely, separate for:half the length of the upper - arm and partially separable to within a few mm. of insertion® The two heads attach by means of a short, common tendon upon the radial tubero­

sity® The tendon of insertion was 1®1 cms® wide and 1*9 cms® long* J Innervations n® musculocutaneus, (Oh), 05, 06 and 07®

’ Gibbon, ■ . . : ' ' . ' - ; ■ ■ • Forms long, slender, fusiform, with two tendons of origin® Positions superficial on the anterior surface of the am® Tendons of Hs Mceps brachii (cont®) origin are covered by the insertion of m0 peetoralis major* Origins short head, arises from the lesser tuberosity of the humerus by means. of a long slender tendon which is fused laterally with the Insertion of mo peetoralis major* longhead^ arises by means of.a.long, rounded tendon which passes through the b ic ip ita l groove of the humerus to arise from the supero-lateral border of the glenoid cavity0 Insertions the two bellies of. the muscle are clearly separable for about one^half of the distance from the long head origin to the insertion* laterally the fibers converge into a longs flattened tendon which passes deep to m. braehioradialis; to .insert'upon the radial tuberosityo Just medial to this insertion there is a well defined- lacertus fibrosus which inserts superficially onto the fascia of the forearm*, There is also a . thickj, wide, fleshy insertion onto the m0 pronator: teres and the m*

flexor caipi radialis (fibers being made up mostly of the short head) * Innervations n» musculocutaneus5 05 to Tl®

Chimpanzee

Fonus long, fusiform, with two long tendons of origin* Position* superficial on the anterior surface of the arm* The tendons of origin are covered by the insertion of m0 peetoralis majore Origins short

head, arises by means of a strong tendon 102 cms0 wide at origins from the anterior border of the coracoid process of the scapulas partially

fused with the origin of m» coracobrachialis* long head, arises from the superior, lateral margin of the glenoid fossa* As the tendon passes through the deep b ic ip ita l groove of the humerus, i t becomes somewhat .rounded* The tendon at the point of origin is flattened^ ■ ■ , ■ hi M® biceps brachii (eont®) . .

The length of the tendon of the long head is 5>®5 eras® Insertions the two heads of the muscle are completely .separable for lij. emso from the point of: insertion of the short head or more than half its lengthy and partially separable , almost to its point of insertion0 The insertion was upon the medial border of the radial tuberosity® There was a

clearly recognized lacertus fibrosusg though not as prominent as that found in man® Innervations m® musculdcutaneuss 0$9- G6 and 07*

M» brachialis (Elate 12) Baboon, Forms longs thi% fusiform® Positions on the anterior aspect of the distal end of the humerus® Origins arises from the anterior aspect of the distal end of the humerus5 along an oblique line which extends from w ell above termination of m® deltoideus on the la tera l side to a point well below the deltoid on the medial side® The distal point of the deltoid insertion meets with the m® brachialis origin at a point 7*5 eras* from the. head of the humerus® The fib ers of the m® brachialis just below the deltoid are continuous with it superficially®. The lateral origin of the muscle extends up to the surgical neck of the bone® Insertions is upon the corahoid process of the ulna by. means

of a long thin tendon® Innervations n® musculocutaneus5 0$9 C6 and 67®

Gibbon., ' '

Forms thick, triangular® Positions on the distal, medial surface

of the humerus® Origins fleshy from the anterior surface of the humerus. Mo braetiialis (cont0) starting ai a point llo5 cm'So from the distal end of the humerus5 just "below the termination of the insertion of m0 deltoidens laterally and extending up the arm some 1 to 2 cms0 beyond the termination of the deltoid medially^ Insertion: the fib ers converge to form a broad f la t tendon 1»8 oms& wide which- inserts upon the coromoid process and tuberosity of the ulnae Innervation: no musculocutaneus5 G5 to fl»

Chimpanzees Forms longs flats ovoid# Positions on the anterior surface of the distal half of the humeruss mostly covered by the m,, biceps# Origins from the distal half of the humerus from about the inferior point of insertion of mc deltoideus nearly down to the epicondyles® The muscle extended for a few centimeters proximallys lateral to the deltoid insertion# The muscle was partially separable into two bellies,' the medial portion having a greater extent of origin from the distal end of the humerus# Insertions the fibers converged just before the elbow and inserted upon the ulna distal to the eoranoid process by means of a broad tendon# Innervations n0 musculocutaneuss C55 06 and 07# '■ - - .

M# triceps brachii (Plate 11) Baboonj,.

Forms long and thickj, with three heads of origin# Positions on the posterior aspect of the upper arm# Origins long head, arises from the ridge separating the infraspinous fossa from the origin of the m# : ' " c : : : ;,%:. : . u? ■ . v';. M-o tricep®:brachii (cont0) v:; ' ;' ■■•■■• ■. ' teres major and. the m@ teres miaor on the axillary border of the . scapulae The origin is fleshy and extends for k°5 cms® beginning a few ?, ' . ' millimeters below the inferior border of the glenoid' fossa*; The inter- relationship with the lateral head is intricateo The fibers arising from near the inferior angle(remain superficial and insert upon the . fascia covering the lateral head# The fibers arising from near the ? r.l glenoid fossa pass ’deep to ;the lateral-hea,d: and llend with it* The long head separates the origins of mm* teres imjor and minpr* Lateral ( ' s; head;,, arises from the posterior aspect of the shaft of the humerus near

its proximal end; just distal to the insertion of m* teres minor* The width of this origin is 2*9 cms* Distal to this the fibers of insertion adjoin the origin of m„ brachialis* Medial head, arises fleshily from almost, all- the posterior,aspect of the shaft of the humerus* Insertions

. the long head and the lateral head fuse within, a few centimeters of : , • _ origin and the’ two muscles insert by means of a broad flat tendon :

Upon the olecranon process-, of the ulna* The medial head i s almost entirely v separate until immediately before insertion where sbrne of the ■ : fibers in sert in common with the other two heads* Other fibers pass . ’ ' deep to the insertion of the lateral head to insert,'Upon the'radial v ‘ . border of the olecranono. The lateral /head inserts along the olecranon ; :

for 1*7 cmses the long head inserts mostly On;tha tip of the olecranon* ■ - (: Iimeriratipn: n* radialis^ 0^ to Tl^, (T2)« . v, -■

M* triceps brachii (Hate 11)

Forms long and flat with three heads of prigin* Positions on .. ' . " . .... - ' ■ ■ . .. ■- 5o M0 triceps brachii (cont®) the posterior surface of the upper arm0 Origins long heads arises by a shorts broad (2o0 erase )s flat tendon from the ventral surface of the axillary border of the scapula up to the inferior margin. of the glenoid fossa just anterior to the origin of m0 teres minor0 Lateral heads arises by tendinous fibers from the posterior aspect of the humerus beginning about 1*5 oms*- below the proximal end of the humerus 0 The la tera l head i s separate from the long head for a distance of about one-third the way down the arm where they become completely fused* The medial heads arises from the posterior aspect of the shaft of the humerus by fleshy fibers starting at a point about one=third of the way down the arm from the proximal end of the humerus» I t fuses almost immediately with the other two heads® Insertions is by means of a broad tendon upon the olecranon process and by a . broad aponuerosis upon the antibrachial fascia on both sideso Innervations zU radialiss G$ to a. : ■

- Chimpanzees ■ ..

.Forms flats oblongs with three, heads of origin® Positions on the posterior surface of the arm® Origins the long head arises by a shorts broads fla t tendon 3®3 eras* wides from the axillary border of the scapula between the origin of m» teres major and m® teres minors inferior to the glenoid cavity® The fibers twist somewhat as they pro- c eed distally and overlap the medial head® The long head is covered above by the spinous portion of the deltoid® The medial head arises by fleshy fibers from the posterior surface of the shaft of the. humerus2 . ' . :: . $1

H# triceps brachii (cont*)- . ■ the upper fibers arising more medially than the lower0 The lateral head arises by means of tendinous fibers above and fleshy fibers belows

from the posterior surface of the proximal end of the humerus9 also from the lateral intermuscular septum0 The long and lateral heads are separate until about halfway down the arm where they are completely fused® The medial heads however, is entirely separate to within a few centimeters of insertion^ Insertions is by means of a stout wide tendon onto the olecranon and by a broad apenuerosis into the ante-= ■brachial fascia on both sideso Innervations a branch of n@ radialis innervates each head separately; to Tl*

dorsoepitroehlearis (Plate 12) Baboon® ' ■ .

Forms /flat,, wide, triangular* Positions on the medial, posterior aspect of the arm* Origins . is complex, being fused with the origin of the long head of m0 triceps and with the insertion of m* latissimus dorsio^ The posterior fibers of the muscle arise from the distal surface of the Bo latissimus dtirsi a few centimeters from its point of insertion*

Proximally some fibers pass over to arise flashily from the origin of the long head of m® triceps, the fibers being continuous with those of m0 triceps® Insertions the fibers converge as they pass down the arm, abruptly forming a tendon about it cms® long® Part of th is tendon

passes la ter a lly forward to insert along the,mc triceps and upper arm fascia6 The tendon passes medially to the olecranon, upon which i t

inserts, then continues distally into the superficial olecranon fascia® . ■'■■■■■/■ . ■■ . ■ 52 Mfr dorsoepitroehlearig (cont>®) ■ - The medial edge of the tendon Is $ cms0 longs Inner-rations n0 radialiss

(Olt)2 05 to Tls (T2)0

Glbhohs - • ' Forms longs slenders fuslform0 Positions on the medial surface of the upper arms bounded by biceps anteriorly and by the long head of m» triceps posteriorly* Origins is from the tendon of m» latissimus dorslg loll cmso from the point of insertion* Insertions an extremely longs slender tendons 11 o 3 cms0 long which is continuous laterally with the intermuscular septumg inserts upon the posterior aspect of the medial epicondyle 0 Innervations n* radialiSs 05 to Tl<,

Ghimpanzees Forms . longs slenders oblong6 Positions on the medial surface of the aims between the m0 biceps anteriorly and the long head of the tri= . .. ■ . -V \’~'- eeps posteriorly * Origins tendinous-s from the medial side of the m*

latissimus dorsi and by a flat aponuerotic tendon from the axillary . ■ - . ■ ■ . ■ ■ . . ■.. ; '■ ^ ■ '-v - border of the scapula in common with the long head of m©. triceps brachii® Insertions the fib ers converge to form a broads f la t tendon (thickened

.on the biceps side)s tik cms0 long which attaches to the posterior aspect of the medial epicondyle* Innervations a branch from n* radialiSs G5 to Tl* 53

Plate 1. Superficial pectoral musculature of an adult female baboon. a, deltoideus; b, pectoralis major; c, pectoralis abdominalis; d biceps brachii. 5U

Plate 2. Superficial dorsal musculature of an adult female baboon, a, deltoideus; b, trapezius; c, latissimus dorsi. 55

Plate 3, Superficial dorsal musculature of an adult female gibbon. a9 deltoideus; b, trapezius; c, latissimus dorsi; d, long head of triceps; e, dorsoepitrochlearis; f, lateral head of triceps; g, teres major. 56

Plate k» Superficial pectoral musculature of the left side of an immature male chimpanzee. a, deltoideus; b, serratus anterior; c, pectoralis major. 57

Plate 5. Superficial dorsal musculature of the left side of an immature male chimpanzee, a, deltoideus; b, long head of triceps; c, teres major; d, latissimus dorsi; e, infraspinatus; f, supraspinatus; g, rhomboideus; (trapezius has been removed). 58

TRAPEZIUS DELTOIDEUS

PECTORALIS MAJOR

PECTORALIS ABDOMINAL IS

SERRATUS ANTERIOR

BABOON GIBBON

CHIMPANZEE MAN

Plate 6« Superficial pectoral musculature (trapezius, deltoideus, pectoralis major, pectoralis abdominalis, and serratus anterior)# CLAVICLE------SUBCLAVIUS------PECTORALIS MINOR

PECTORALIS ABOOMINALIS

SERRATUS ANTERIOR

BABOON GIBBON

CLAVICLE SUBCLAVIUS PECTORALIS MINOR CORACOID PROCESS SERRATUS ANTERIO

CHIMPANZEE MAN

Plate 7. Deep pectoral musculature (subclavius, pectoralls minor, pectoralis abdominal!s, and serratus anterior) Hate 8. Superficial dorsal musculature (trapezius and deltoideus).

§ LEVATOR SCAPULAE

RHOMBOIDEUS PARS CAPITIS RHOMBOIDEUS .. CERVICIS THORACIS MINOR MAJOR

L AT I SSIMUS LATISSIMUS DORSI DORSI CREST OF ILIUM

BABOON GIBBON CHIMPANZEE MAN

Elate 9» Deep dorsal musculature (rhomboideus and latissinms dorsi). SUPRASPINATUS SUPRASPINATUS

INFRASPINATUS INFRASPINATUS TERES MINOR TERES MINOR TERES MAJOR TERES MAJOR

BABOON GIBBON CHIMPANZEE MAN

Plate 10. Intrinsic musculature of the scapula (supraspinatus, infraspinatus, teres minor and teres major).

s BABOON GIBBON CHIMPANZEE MAN

Plate 11. Intrinsic musculature of the ventral surface of the scapula (sub scapular!s and long head of triceps). CORACOBRACHIAL! S CORACOBRACHIALIS PROFUNDUS MEDIUS TERES MAJOR TERES MAJOR LATISSIMUS DORSH LATISSIMUS DOR SI PECTORALIS MAJOR

DORSO-EPITROCHLEAR ONG HEAD LONG HEAD SHORT HEAD SHORT HEAD OF OF BICEPS BRACHII BICEPS BRACHII

DORSO-EPITROCHLEARIS

BRACHIALIS BRACHIALIS

LACERTUS FIBROSUS LACERTUS FIBROSUS

U. BABOON GIBBON CHIMPANZEE MAN

Elate 12# Brachial flexor muscles (coracobrachialis, biceps, brachialis, teres major, latissiinus dorsi, pectoralis major, dorso-epitrochlearis)• Chapter Toiar

. Comparative Morphology of the Brachial Plexus The gross morphology of the brachial plexus of the baboons gibbon and'chimpanzee i s considered in th is chapter* I t was often difficult to determine fine points of.innervations thus only the larger details of composition and distribution of the brachial plexus are presented* -- Changes in the complexity of origin and insertion and in size of muscles are not accompanied by broad changes in the nerve supply. Thereforeg it is difficult to perceive trends of far reaching evQlu~ • tionary significance in the brachial plexus of the primates* The inter**- pretation of differences between the distribution of nerves in the various forms is thus limited to a consideration of functional relation** - . - - ■ ; . . ■ . ■ - ships*

Reference to the illustrations of the brachial plexus (Plates 13glli) readily shows some of the ,broad sim ila rities in the plan of th is structure among the primates* The plexus of the rhesus has been well described by Howell and Straus and, because of i t s obvious sim ilarity to that of the baboon# is not included here* apxx,::.:# .

The drawings of the plexus are to be considered schematic only* Gray’s Anatomy was used as a reference for the sketch of the human brachial plexus# although the drawing has been modified somewhat* . The placement of the peripheral" nerves is accurate as regards the number of spinal nerves which could possibly contribute to the nerve* However# ■' . ■ ; . 66 the relative distances between the junctions of nerves is only approximately correct6

Baboon, left brachial plexus, (Plate 13) The brachial plexus of the baboon i s remarkably sim ilar to that of the rhesus monkey (cf = Howell and ■ Strauss 1933 s 3H -317)» The major portion of the plexus is made up of the fifth to eighth cervical and the first thoracic spinal nerves0 In addition, there is a slight contribution from Gk and a heavier one from T20 The spinal roots give off a number of nerve branches before going on to form the plexuso

Very near the foramina o f ex it of roots §3 to 08, small nerves are given off which go to innervate the rm» sealeni and longus colli, (not illustrated)6: In addition, the n» thoracalis longus, which innervates the thoracic portion of m® serratus anterior, is made up of branches from C5 to 08 roots® The f ormation of trunks and cords i s broadly comparable with the condition in man, the chimpanzee and the gibbon® The f if th and sixth roots unite just lateral to their foramina of exit, after the communis eating branch from Clj, has joined C5>, to form the superior trunk® The middle trunk is formed by 07 alonej and the inferior trunk is formed by the union of 68 with T1'after the latter has received a communicating branch from T2S

' The trunks divide soon after formation into ventral and dorsal divisions® The two anterior cords, lateral and medial, ’ are formed from the ventral divisions of the trunks® These cords are both rela­ tively long, anasthomosing distally for a short distance prior to w dividing into the terriiinal median and ulnar nerves. The posterior cord is rather short, terminating in the large radial nerve, ' ■ , The nerveh: arising from the anterior division are as follows % : t,

t ' Nn, thoraeales anteriores/ arise from the lateral and medial . cords3 (04)5 G5 to Tig (T2) roots.® The loop formed gives off three nerves which goto the pectoral muscles® The branch to m, pectoralis major divides ±hto three twigs which enter, the medial, distal fibers , -■ of the muscleo A single branch' goes to m®- pectoralis minor and one to m, pectoralis abdominalis& 1: , / • • . ... ' t.: V 1 t. > :h :t .V : .No' sub c lav ins 5. arises from the lateral cord near the juncture of ' .05 and 0.61 it may contain elements from (OS) as well. The nerve passes directly to innervate the ma. subclaviusi .1 1, supraseapularisj, .arises from 0^ root distal tO rlts' union with the branch from Oij.« I t . passes over th e. broad scapula notch to innervate the m, supra spina tus g then through a large foramen'cnear the lateral-, end

of the base of the scapula; spine id ..innervate m, infraspinatus, - . .. N® musG'ulocutaneusj arises from the lateral cord, (Gl|.)? 05, 06,1 and 0? roots,. It passes- down the medial side of the upper arm, giving l off branc he s to innervate - mm, eorac obrachialis profundus e t medius, ■ before continuing down the arm to ■ innervate mm, biceps and"brachialis®. - In, medianus and ulnaris, arise from the la tera l and medial cords. They probably include increments from all the spinal roots, Cli to T2, -

- according to experiments by Sherrington, the part of T2 going to the ? -: plexus inrhesus contributes motor fibers to these two nerves only,

(Sherrliigton, (1898) c it , in Hartman and Straus, 1933 $ 31% Presumably 65 the same situation is true in the baboon* Inasmuch as neither the median nor the ulnar nerve contributes to the shoulder or upper arm musculature9 they w ill not be discussed further® ■The nerves arising from the posterior division are as follows: . N* dorsalis scapulae^ arises from 05 root d ista l to it s anasthamosis with the branch from Ob* The nerve divides almost immediatelys sending one branch to innervate the cervical portion of m* serratus anterior* the other pierces the bu serratus anterior and is distributed to the three portions of m* rhomboideus* Hni: subscapularesg arise from the posterior cord just distal to the juncture of the dorsal divisions of Gi> and 06 with that of C?® ' 'V . ' T These two branches pass immediately dorsalward to innervate the

. ■ ; ■ : : ■ ; ■ . / ■ subscapulariso

No axillaris* arises from the posterior cord* distal to the nn® subscapulares* 05* 06 and 0? roots® The nerve immediately divides into two branches* one of which passes directly to m0 teres major to innervate it; the other branch passes between m0 teres major and the mmo cordcobrachialis profundus et medius and splits* sending one division to innervate the m» teres minor arid the other to m« deltoideus N. thoraeodorsalis* arises from the posterior cord* near the junction of the dorsal division from 08 and Tl® It passes dorsalward and caudalward to enter the m® latissajaus dor si near it s d ista l end®

No radialis* arises from the posterior cord as the terminal nerve of the plexus; it may contain elements from all the spinal roots* (Git)*

05 to Tl* and (T2)0 The nerve passes out into the arm along with the other major nerves# bmt about halfway down the humerus it twists laterally to the dorsal surface of the arm where it innervates the three heads of m* triceps and the m* dorsoepitroehlearls by separate branches & It then passes down the ara to supply the extensor muscles of the forearm and hando ■ Gibbons left brachial plexus# (Plate 13) The brachial plexus in the gibbon is composed to the anterior primary divisions of the fifth to the eighth cervical and the f ir s t thoracid spinal nerves as in man a So contributions were observed coming from either the fourth cervical or the second theracic root*

The spinal roots give off a number of nerve branches before coalescing into the three major trunks* Veiy near the foramina of e x it of the seventh and eighth roots# small branches are given off which go to supply the mm* scaleni and longus colli (not illustrated)® The m* thoracalis longus# Which Innervates the thoracic portion of m» serratus anterior# i s made up of branches from C6 and G7 roots* The n* suprascapularis# which supplies the mm* supraspinatus and infraspinatus# arises from the fifth cervical.root as do contributions to the mm® rhomboideus and levator scapulae®

The f ormation of the trunks and the cords is regular® The fifth and sixth roots unite just la tera l to the foramina of ex it to form the superior trunk; the middle trunk is formed by the seventh root alone; and the inferior trunk i s formed by the anasthomo'ses of the eighth cervical and the first thoracic roots® .

The trunks divide almost immediately after formation into ventral and dorsal portions o The two anterior cords of the plexus are formed .70 from the ventral divisions of the trunks^, and the posterior cord is composed of the dorsal divisions* fhe tw anterior cords are very shorty anasthomosing almost immediately after formation into a long combined anterior cord* The nerve branches given off by the anterior cords mainly innervate the pectoral and the ventral arm rausculatures while the branches from the posterior cord go. to innervate the smperficial back and the dorsal arm musenlatureo

• ■ ■' ■■ '■ ■ . ■ = : ' ' : The nerves of the anterior group are as followss Nn* thoracales anteriores, arise from the la tera l and medial cords*

One branch arising from 08 to-T1 roots9 and the other from 05$, 06s and 07 roots o The combined nerve is distributed by three twigs which go to m* pectoralis major and two twigs which go to the m0 pectoralis ininor* Mo subclaviusg arises from the lateral cord near the trunk formed - by the junction of 05 and 06« The nerve is distributed solely to the Mo subclaviuse

Mo coraepbraehialiSs arises from the combined anterior cord, near the juncture of the lateral and medial cor deg and could be composed of elements from G5 to C8 and Tla It passes directly to innervate the mo coracobrachialiSo ' Mo musculocutaneus$, arises from the combined anterior cord near the division into medial and ulnar nerves* This nerve, eduld possess elements iron 05 to 08 and Tlo The nerve divides almost immediately$, sending one branch between the two heads of the m* biceps to innerVate this muscle near its proximal end* The other branch passes down the am : to innervate the brachialis muscle6' •

Mh» medianus and ulnarisa arise from the lateral and medial cordsa :w±&- elements froitt all' five spinal roots. They pass dox-m the medial side of the arm to the foream muscxxlature^ and. as they do not innertate any of the upper am riiusculatnres they are not considered further@ . - '. ;

. : v'.;vx.::: --..'fhe nerves, of the posterior group are as follows: Nn= subscapulariss composed of three separate nerves arising from the dorsal division of O^ and G6 combined^ These are distributed ; ;

directly, to the medial belly of m, subscdpulafisg • No axillaris9 arises from the posterior cord, 0j?<> C6$ and G7 roots0 It s p lits .into two'nervesp one of xhiich. innervates the m0 teres minor$

while the Other inhervates the m* deltoideus as,well as sending cutaneous

branches to the posterior shouldero : ■ ' : ■ No teres major3 arises from the juncture^ of the axillary nerve withthe'posterior cord5 Gh5 - G6 and 07 spinal rootso This nerve passes ■ : directly dorsalward to innei^ mo teres man or 0 : No thoracodorsalisj arises from the posterior cord| C8 and T1 roots It passes dorsal to the, long cords of the plexus and thence directlyto

the medial portion of the m0 latissiraus dorsi which it innervates0 I® radialis3 is the terminal nerve of the posterior-cord3 thus i t ' contains elements of a ll the spinal roots» , The nerve passes dovm the ' arm to innervate the itu dorso-epitrochlearis and the long head of mo :: triceps near their proximal endss and the lateral and medial heads of . ; . m triceps further down, the arm* It then continues • into .the forearm to

: i , ' " ' : : ^ vsx^i^r the'extensor ;musclesi®iy:^y.,xi\^

left brachial" plexusy Cllate ll|.) ' y ' ■ ' V- d „ y ; y The left brachial plexus in the chimpanzee is very similar to that : V V - : ■ - V : ■ 72 in man* . The plexus is made up of the anterior primary divisions of the fifth to eighth cervical and the first thoracic spinal roots» There is a small branch which communicates with the plexus from Gl^ but a branch from T2 is definitely lacking* A number of nerves are given Off from the spinal roots before they anasthomose into the primary trunks*- from 66y • ,07# and Go roots small twigs are given off which supply the am* scaleni and longus colli (not illustrated)* The n* thoracalis longuss which

innervates the thoracic portion of m* serratus anterior^ is made up of

contributions from G6S 07$ and 08* The n* suprascapularis5 which supplies the Bim* supraspinatus and infraspinatus^ arises from 05 root, as do small contributions to .the mm* rhomboideuss levator scapulae and the f i r s t two digitations of m* serratus anterior* The formation of the trunks and the cords i s comparable with the

situation in the gibbon and man* The superior trunk is formed by the ' juncture of 05 and 06$ including a contribution from 0)4.1 the middle trunk by 07 alone5 and the inferior trunk by the anasthomosis of 08 and

nVV ' The trunks divide almost immediately into ventral and dorsal divisions* The two anterior cords of the plexus are formed by the ventral. . divisions of the trunks and the posterior cord is composed of the dorsal, divisions* The two anterior cords are shorter than in man, but longer than in the gibbon* Almost immediately after anasthomosinga they branch

into the large median and smaller -ulnar nerves* The posterior eords which

terminates in the radial nerves is also quite large* The anterior division gives rise to the following nerves?

in* thoracales anterlores$ arise from the medial and lateral cords$ ‘ Oae.ybranch being given off by 07 and the other by the combined'; 08-and ■ . Ti roots 0 The nerve passes doim the anterior, thorax. to supply the ,

. pectoral mnscles^ : ;; -

; p subclavimSj, arises from the lateral cord near the trunk formed

- by the juncture of Cl|.s C $ 9 and Q6« It innervates the m® subclavins •

; ; ■ ; ■ ■: ; . -v-v:; 'y\:-v ; ; ; ; il0:imrscnlocntaiieus$ arises" from the medial cord, (Git), 0 ^ 66, and

07 rootso A small branch from this nerve passes into the proximal portion of m. coracobrachialis. The remainder of the nerve passes down the arm to innervate the mm» biceps and brachialls. ' v 1 " :V'-l f . V ; :: r •f-f-.-r ' ; / f ' : Nn« median!s and nlnaris, arise from the lateral .. arid medial cords j n» medianis coming mostly from the middle cord and ns ulnaris coming ;

mostly from the lateral c ord» Npwever, both nerves: probably contain If:

' . ' elements from all the spihal roots.® As these two nerves do not inhervate any of the upper arm musculature, th eir distributiph i s not considered further*

® :' The' posteribr fd,ivision'glyesiri^ nerves: : : - -fl/ ' f ;; : 1;;• Nn0 subscapulares, two separate nerves arising from the dorsal

division of (Gl|.)s 00 and G6 combined6 The separate nerves pass to the

substance of the Hu subscapularis which they innervate* \ : f - N« axillaris, arises from the posterior cordj. (Gij.), 05, 06, and , .07 rootso It innervates the m® teres minor and the m® deltoideuso f ' f N* teres major, arises from the posterior cord between the nn® sub=

scapulares and the n* axillaris, (0%), 0$, 06,-and 0? roots. This herye:

passes director tb iimeryate the m» ; teres major* u'

. No thorac odor sa ils 5 arises from the posterior cord, 08 andTl roots® This nerve enters the substance of the upper part of latissimus \ .

dors! to innervate it » 1® radialiss the large terminal nerve of the posterior cord* contains elements from a ll the spinal roots® This nerve supplies the long head of m® tricep sa and the m® dorsoepitrochlearis near their proximal ends,, and the lateral and medial heads of m® triceps further down the arm® The nerve then passes down the arm* presumably to inner- - vate the extensor muscles of the forearm and hand® . v

Summary of the brachial plexus

The brachial plexus in man is closely related to those of the other primateso There is a greater similarity to the plexus of the apes than to that of the Old World monkeyss especially in the number of spinal roots which make Up the plexus and in the formation of trunks and cords® There are a few observations which may be made concerning nerve-muscle relationships® Although the m® levator scapulae is considered a part of the serratns muscle sheet* it receives a separate nerve supply from the n® dorsalis scapulae® . However* the spinal root which supplies this nerve also adds to the n® thoracalislongus which goes to innervate the ■ serratns muscle® The relationship of the m$a® atlantoscapularis posterior and anterior (omocervicalis) to the m® serratus can also be inferred on the basis of innervation®

The m® occipitoscapularis of the rhesus and the baboon is related to the m® rhomboideus and receives a branch from the n® dorsalis scapulae which also innervates the rhomboideus® The pectoralis: sheet receives its nerve supply from the n® The close relationship, between, the m,a '4orsdepTtrociilearis and : the mo triceps can be inferred from the observation that the innervation

is sianilar* ;• rBoth 'the; long head of the triceps and the Bio 'dorsoepitroch” learis receive a branch from the radial nervea ; ' ' The innervation of the brachial flexor muscles inthe gibbon deviates somewhat from the normal.pattern for the rest of the primateSs ’ There is a separate nerve to the eordcobrachialis muscles and the true. musculocutaneous nerve is very short3 dividing almost' immediately after - formation to. send one branch -to. the m„ brachialis and the bther branch' to the two .heads of the m0 bicepsl ; , . . - ^ :- In generals it may be said that the form of the brachial plexus: ; is determined to a: degree by the general morphology of the pectoral V- musculatures and the conformation of the thorax6 Thus, the trunks and cords are longer in the apes and man than in the monkeys due to the greater lateral displacement Of the shoulders« ' : 1;' :: ' - : t 76

,DORSAL SCAPULAR BABOON SUPRASCAPULAR JBCLAVIAN_ SUBSCAPULAR AXILLARY TERES MAJOR

RADIAL THORACODORSAL MUSCULOCUTANEOUS

MEDIAN ULNAR ANTERIOR THORACIC

LONG THORACIC

DORSAL SCAPULAR ^SUPRASCAPULAR GIBBON ^SUBCLAVIAN TERES MAJOR <

ANTERIOR THORACIC LONG THORACIC

Plate 13• Left brachial plexus of the baboon and the gibbon, CHIMPANZEE

DORSAL SCAPULAR ^SUBSCAPULARS ►SUPRASCAPULAR/ ^SUBCLAVIAN/ TERES MAJOR f AXILLARY

RADIAL THORACODORSAL

MUSCULOCUTANEOUS — " ' " ^ MEDIAN — I ULNAR

ANTERIOR THORACIC LONG THORACIC

C4

C5

C6

C7

C8

T I

Plate lit* Left brachial plexus of the chimpanzee and man* 78 Chapter Five V ' Comparative Osteology • The close relationship between osteology and neology cannot be

disregarded in a study of this sort6 It is well known that- changes, in the morphology of musculature induces changes in the sk eletal frame» •work® Experimental proof of this is to be found in the work of Wash-

bum (Washburn* 19l|.7) and h is students (Wolfson* The vertebral column* the sternum* the ribs* the scapula* the clavicle* and the humerus are a ll intimately connected functionally*

For comparative osteological purposes we w ill be concerned with three of these structures* the scapula* the clavicle and the humerus*

Scapula* (Plates 15* 16 and 17) The scapula of a ll the f orms being considered :in this paper can be described as a wide* flat* triangular bone* possessing two surfaces*

dorsal and ventral| three borders* vertebral* axillary and cephalic! three angles* inferior* medial and lateral! and four major processes* coracoid* acromion* spinous* and glenoid*. '

In terrestria l quadrupeds such as the cat (leach* 19li6)* the

scapula is a greatly flattened* triangular bone* elongated along its glenovertebral axis* The supra- and infr&spinous fossae are of nearly equal sise* The vertebral border is rather evenly convex from the

acute* inferior angle* to the rounded* medial angle*

. ’ The scapula of. the rhesus follows this generalized pattern in some respects* hut presents some specialized differences* The glenovertebral ■axis is still the longerj however, the cephalocaudal axis is somewhat ;

increased® ; There is a marked difference in the size of, the supra- ■ - ' and infraspinous: fossaeo The supraspinous fossa is reetanguloid and , ,

smaller® The ventral surface of the scapula is smooth and flattened* - The vertebral border is evenly convex for its entire length® The ' . ■- 'Vir.';' ; ;f:: k'l:' ;; y --k .....' cephalic border is elongated, and irregular, , and possesses a yd-de, ■ .:. ' shallow, scapula notch at the lateral end® •. The axillary border is wide;

and elongated® The inferior angle i s obtuse and the media]/ angle vk/y approaches a right angle® There is a large,- rectangular, inferior angle fossa for the origin of mQ teres major® ■The coracoid and acromion

processes are both relatively smooth and slender® The spinous process is long and wide, and extends laterally from the vertebral border almost to the lateral: best

be described as resembling a .larger circle intersected by a smaller - ^ ellipse, the cranial portion being smaller® -' The caudal portion of the cavity is deeper and more concave® ' k '.v y ... .'vC-...-'..'-.. -: ;y ' : ' T y- - n i : .. f ' ' '/y " . v . . , The cephalocaudal axis is kmcreased ln the: scapula of the baboon :-y '• to the point where it nearly equals the glenovertebral axis® The supra™

and infraspinous fossae are more nearly the same size, with the supra- . ■k -• ' spinous fossa being; only slightly smaller® -The .ventral surface, of the- scapulais somewhat more concave than in th e rhesuso . The lower portion of the vertebral border is straight, - while' the portion from the root of the scapula spine to.the medial:angle is convex® The cephalic border " is shorter than in the rhesus and evenly concave for its entire length®

There is no cti.fferentia.ted scapula notch® The axillary border is broad, but shorter than in the, rhesus® The inferior angle approaches a right ' ' 80 aagle3 ifliile the medial angle i s broadj. rounded and ohtuse* The inferior angle fossa for origin of m« teres major is larger and some™ what better developed than in the rhesusOn the ventral surface of the inferior angle there is a small triangular^ roughened area for the attachment of the tendinous portion of m serratus anterior® Both the coracoid process and the acromion are slenderer and less rugged than in the rhesus® The spinous process is broad and extends from the vertebral border to the lateral angle® In shapes the glenoid cavity is almost identical with that of the rhesus^ although relatively smaller® In the gibbons the cephalocaudal axis of the scapula has definitely increased in length over that of the glenovertebral axis® The supra- and infraspinous fossae are of nearly equal size® The. ventral surface i s markedly concave along the cephalocaudal axis® , The vertebral border is straight, for almost its entire length and parallels the vertebral columno The cephalic border is deeply concaves but possesses no definite scapula notch® The axillary border is narrower than in the rhesus or the baboon® The inf erior. angle is broadened and is slightly greater than a right angle® The inferior angle‘fossa for the origin of m® teres major is reduced in size® The medial angle, is less broad than in the baboon and is more acute® The acromion i s longers b etter developed and greatly increased in size over that of the rhesus or the baboon® The medial border of the acromion extends much more laterally than in the rhesus,, the baboon, or man® The coracoid process is longer and slenderer than in the rhesus or the baboons. and not as massive as in the chimpanzee or man® The,spinous process has increased.in sizes is more triangular in shape and is directed obliquely upward® The root of the. spine does not -81

extend to the vertebral border<, and the oblique direction of the spine tends to increase the size of the supraspinous fossa* The glenoid .. ' ' . . : cavitj is ovoid in shape and is somewhat intermediate in conformation between that of the monkeys and ‘that of the chimpanzee and man* The scapula of the chimpanzee most nearly approaches the dimensions and shape of that of man® The cephalocaudal axis is greatly

increased oyer the glenovertebral axis® Both the supra- and infra- spinous fossae are increased in sizes but the infraspinous remains the larger= The vertebral border is nearly straight for its entire length and parallels the vertebral columnQ The cephalic border is much shorter and more deeply concave than in the rhesus^ baboon, or gibbon® At the lateral end of the cephalic border, there is a wide, deep scapula notch* The axillary margin is broad and long® The Inferior angle is broader and approaches a right angle® On the ventral surface of the angle is a small, roughened, triangular area for the tendinous insertion of m0 serratus anterior® The inferior angle fossa for the attachment, of m0 teres major is small and triangular® The muscle now. arises from the dorsal surface of the broadened inferior angle® The medial angle is sharply acute® The acromion process is short and heavy® The acromial articular surface is ovoid and very distinct® The entire width of the acromion extends la tera lly beyond the glenoid cavity® The coracoid process is relatively more massive than in the rhesus, baboon, or gibbon, but slenderer than in man® The spinous process is short and directed obliquely upward, thus increasing the size of the supraspinous fossa®

The root of the scapula spine barely reaches the vertebral border® The glenoid cavity is egg-shaped in outline and rather evenly concave® It i s generally broader than in; She rhesus^ /baboon5 or gibbon,

Glaviclej, (iiot iilmstrated) \ y-' : - The clavicle in all f orms being considered is a slender ourved

bone which acts as a :fulbrumvtio' enable; the; muscles to give - laterai % motion to the am® - It is divisible intd. a Shaft and two eztremitieSg sternal and acromial® . ' b ■ : v y. : : / yy- - -yvyy v ; - ,y. . >:y, The.clayiole of the rhesns is a shorty singly curved bone with a slender shaft0 The- sternal end is considerably thickened and ends . in an ovoid shapedj.. shallowly convex articular., surface® ' The acromial extremity is flattened and only slightly broader than the shafto The

acromial articular surface is roughly semi-circular in outline® ;The ; ,. . shaft is relatively smooth and is not characterized by distinct,,

■. roughened areas for muscle, or ligament attachment0 v There I s a notice^ able absence of a coracoid tuberosity for attachment of a conoid lig­

ament® y/' V /V'-: d.^;. y :y ' / ' i d - -'"id d' " - ,-d\ ■ ' The clavicle of the baboon i s Markedly stouter, and is slightly, longer than that, of the rhesus® 'The hone i s approximately 3 -shaped,, . . : ;y - . y ; ■' . ■ ■' ' '. ‘ y 7 ' ' ■ ■ - ;d: '' \ y -y ' - the medial half is bent convexly ventralward while the lateral half-.is

bent convexly dorsaiward®: The." sternal end expands considerably towards the articular surface <, which is roughly triangular in outline® The .

acromial end is somewhat flattened cephaloeaudally. and expands only : slightly tcwa^s the oydid articular: surface. There is a marked ridge d on the cranial border of the acromial end for the1 insertion of the m® trapeziuso

The gibbon clavicle was destroyed during.the embalming and -

eviscerating■process9 so, that # is impossible to giveany personal observations on this structureo . • : . :/ :' : . ; : ■■ - - ;: • • The clavicle ot the chimpansee is mrkedly longer than in any '■ ; V ' : \ \ "■ ; ■ v /-; ' of the, other forms discussed ;prevlonsly= However5 Schultz reports - that oh; the average the chimpanzee has the relatively shortest clavicle of the four largest primates (Schultzs 1932s 336)0 fhe shaft, is • relatively heavy and is markedly S-shapedo ' The medial two-thirds of the shaft is bent convexly ventralward^ while: the lateral one-third, is sharply bent convesly dbr sal#ard.o The sternal end. Of the clavicle expands only slightly to form a deeply concave ovoid articular surfaces This sternal articular surface appears to be relatively smaller than 'in; the rhesus and the baboons : The acromial end.is considerably wider ■ and more massive than in the Other forms* The acromial articular surface is : ovoidj and, appears to be relatively larger than in the rhesus or baboon® The areas of attachment for the mm® trapezius and deltoideus are'quite pronounced® There is a rugged coracoid tuberosity on the . caUdal margin of the clavicle® ■ y , : _ • V ; -

The cla v icle Of. man is sim ilar to that of the chimpanzee s but

The humerus i s the long bone of the: arm which articu lates with the glenpid cavity Of the scapTiLa above and .with . the two bones of the forearm below® It is divisible into a shaft and two extremities® The' upper extremity includes the heads the neck, the greater and lesser : ■ ■ ;:y • . y ;":y; y ; . " b tuberosities, the intertubercular groove and the crests of' the tuberos­ it ie s ® The lower extremity includes the articular surface; and two suraemtlng fossa s the anterior coronoid and the posterior olecronon,, : as well as two epicondyles5 medial and laterals' „ / ; In the terrestrial quadrupeds such as the cat (leach; 19k6$kk)$ the humerus is short and stoutj the head•is flattened and the greater; and lesser tuberosities extend above the head on either : side» The • - . ^ intertubercular.groove is wide and shallowo: Above and on the inner

- margin .of. the d ista l end, i s a' large foramen through which the median f nerve passeso The coronoid fossa is shallow and indistinct0 The mediai epicondyle; is large and pointed* The lateral epiebndyle is /

,•’.smaller® ; t :'v '■ , • t v' ^ ■ The humerus of the rhesus monkey^, especially the proximal ends . ’ approaches that of the te r r e str ia l quadruped in form0 It. i s a short stout bone® The head i s almost a hemisphere and. i s situated below the greater and lesser tuberosities® The intertubercular groove is wide 1 and shallowo The crest of the greater tuberosity extends down the shaft of the, humerus for about, half of it s -length and is d istin ctly rugged® /

The crest of the lesser tuberosity is shorter, less distinct, but con- : siderably rougher0 The deltoid crest is relatively, distinct and occupies a position just proximal to the middle of the lateral surface. The articular surface of the distal end of the humerus consists of two processes, trochlea and capitulum® The trochlea is nearly a truncated cone in shape, but is slightly concave and possesses a faint ridge oh

;the v e n ti^ is globular in form and has ventral and distal surfaces. The olecrdnbn fossa on the dorsal face, proximal ' ' y - Y ' / ' . , ,■• Y . . x : Y f Y - '• .■■■'. ' 1 ■ Y._. ■ ’• : YY : ■ . Y < - to the articular surface is deep, and ovoid, in outline® The coronoid - ,:-85 . v: fossa on the ventral surface5 just above the trochleaj, is shallow and r; indistincto ' The medial epicondyle is a large, rough tuberosity some- 1 what:dorsally placed„ The lateral epicondyle is smalls rough, and : : ventrally situated® It is continued proxiraally as a well defined . epicondylar line for about one-fourth of the length of the bone®. In raany respects the humerus - of the baboon is identical with that

. of the rhesus® It is somewhat shorter and stouter, especially at the i ; proximal end® ;The head is sub-hemispherical and similarly situated . .below the greater and lesser tuberosities0 The intertubercular groove

i s somewhat, narrower but. about as deep as in the rhesus® The crest of '. the greater tuberosity is heavier arid more distinct than in the rhesus® - It extends down the shaft -fop' about one-third of the ' length® ' The crest of the lesser tuberosity i s considerably smaller and smoother than in \ > d" ' Vi'h-v ' ' - ; :■ .'1 ; , ■/ ' : : the rhesus® . The deltoid crest is much longer and more . distinct, but is

... s t i l l , proximal, to- -the middie of the la tera l surface o f ;the shaft® On the distal end of.the humerus, the shape and size of the trochlea gnd eapitulum are identical with.the rhesus® The olecronon fossa, however, ' is deeper and somewhat triangular, in shape ® The: coronoid fossa is less distincto The medial epicondyle is slighter and less rugged® The 1 - : " •. - ■ • . lateral epicondyle is slighter and less rugged,.but the epicondylar line d: i s more pronbuncedq . ' , t.:; -

' ‘d ;; d The humerus. of the gibbon presents a strikingly different picture

. when' c b ^ It is a long, slender bone with very poorly marked surface characteristics® The head i s hemi-

spherical and has greater relatlye. surface, area than in the rhesus and

baboon® The greater arid lesser' tuberosities are situated^ubt M ' head on the lateral surface®' The intertubereular groove is romdeds . narroTAT and deep* The crest: of the greater tuberosity i s slig h t and . . poorly developed* extending about one-half of the distance doim the shaftt The crest of the minor tubercle is very short and indistinct. The deltoid crest is proximal to the middle of the lateral surface and - : is about as heavy as the crest of the major tubercle. On the' distal •. end the articular surface shows some major changes over the rhesus and the baboon. The trochlea is somewhat hourglass shaped* ;with a distinct ' ridge separating it from the capitulum.0 The capitulim is globular* but '' tends to be more ventrally situated with less of a distal surface. The ; olecronon f ossa is deep* ovoid and somewhat medially placed*:due to: the widening of the medial epicondyle. The coronoid fossa is circular in ' outline and more d istin ct than in rhesus or the baboon. The medial epicondyle is large and trapezoidal in shape. The lateral epicondyle is. smaller and though the epicondylar line is distinct* it does hot .extend;

very far proximally, . : ■ .d : \ :' d ' ^ ' ; 7. The massiveness of' the humerus, of; the chimpanzee' i s one of i t s d most distinctive characteristics. The shaftiis heavy and cylindrical :above and. vmd shaped belew. The surface markings are' rugged and' d. - ' % d istin ct. The head of the humerus i s large and rounded* • somewhat heitii- d' r dd- 'd. - \ ' -/ " - . 'd ■ d'd " ■" '' ' . ddd ' ' . ' sphericalin shape, Thegreater and lesser tuberosities are situated slig h tly below the head. The intertubercular groove i s rounded*deep and narrow* as-in the gibbon. The crest of the greater tuberosity is a ' ' . heavy, ridge vdiich extends two-thirds of 'the . way dom the shaft of the humerus. The greater tuberosity itself is : relatively larger and rougher : ' ' 'V'"'- ■ ' ddd -d ■ - ;'d: '''::’d . d , . : :"d .. \ ' dd'dd ' ddd d '-ldd’ J;; ;; than in rhesus* baboon* dor gibbon* but smaller than In man, The crest : ; ' of the lesser tuberosity is broad and distincto The lesser tuberosity ’ proper i s massive in comparison witharry of the other forms studied^ ' - including man0 The deltoid crest is- proximal to the middle of the . lateral surface^ It is less distinct than in the rhesus5 baboon or man, ■ - vV:v'ri" i ^ ; ;. but more distinct than in the ;gibbon« 0n ;ihevdis^l- ^.end".. the' trochlea ; is hourglass shaped as in the gibbon and marie The eapitulum is globular h and more similar to that in man than any other of the other forms under ' consideration,, The olecronon fossa is large and deep, and is pierced by y \ V a small forameno ' The coronoid "fossa is' rounded^" deep and very distin cte . The medial epicondyle is larges roughened and somewhat rectanguloid in outline. It is relatively larger than -in mans gibbons baboon or rhesus, ■ ; - . The lateral epicondyle is. large'and bough* The epicondylar line is : ; * markedly distinct^ considerably wider than in man.or-the other forms® - There, is a marked tendency for the distal end of the humerus to increase " in relative width from the rhesus up to the chimpanzee, . ' In manj, compared with the other forms, the head" of the humerus i s . v relatively larger, the deltoid crest is more marked and rugged and the -

major tuberosity i s larger. The intertubercular groove-is narrower and - deeper than in the monkeys, but hot as narrow or deep.as intheapess

' - articular * suhfaee i is. ^largdr^- ^ah are the olecronon and coronoid fossae,’: Ruth filler reports a :generalized trend for the head of;the ., ■ humerus to rotate medially so as to be in almost' the same plane as the

■ condyles from the monlceys tlirough the apes to man (M iller, 1932s36) c.

Comparative Structure of the Pectoral Girdle, (Plate 19 and 20) There are marked differences in the.conformation of the shoulder • ^ - ‘ l-.-fP : girdle:as a structural unit as well asinthe individual bones, Schultz

>-v: has presented several admirable summaries of these changes in numerable articles/ so that only a few of the more important points w ill 'be ‘ . briefly mentioned here (Schultz,, 1936s .195>0) a ;• / .,. .y : . ; \ The dimensions of the thoracic cage of the anthropoid apes and man hare increased in transverse diameter over the anterior-posterior diametero In the rhesus, and the' baboon these two dimensions are

. ■ ■ ■ ■ . approximately equals Correlated with this., flattening of the chest is a broadening of-the sternum/ There is also evidence of partial fusion ■ of the separate;bpnes: of the body of the sternum in the great apes and complete fusionin -adult' man« v- In' the rhesus and the baboon the parts . of the sternum are normally separate® The average number of ribs

attaching to the sternum is also seen to decrease, from the monkeys to - .the apes/ with:-man occupyingian intermediate .position®; -V .' -- : ' •With the broadening of the thorax' there are associated changes ■ in the position of the scapula® The scapula of the rhesus and the baboph' lie s on the lateral wall of the rounded thorax, with the glenoid cavity facing somewhat ventrally® It is joined to. the sternum by the short g slightly curved clavicles® . : - ' . The position of the scapula in the' apes: and man is upon the . dorsal -surface of the .thorax'-withithb glenoid' cavity facing lateral- ward®. The clavicles:have increased in length and are now doubly curved The shoulders are situated .above the suprasternal notch so that the. clavicles are directed obliquely upward' in 'the apes, a condition which lends to the impression of permanently shrugged shoulders® In man, th e clavicles are nearly horizontally directed Ut. rest® ' SUPERIOR ANGLE ACROMION

SUPRASPINOUS CORACOID PROCESS

VERTEBRAL GLENOID BORDER CAVITY

AXILLAR INFRASPINOUS BORDER FOSSA

GIBBON INFERIOR ANGLE

Plate 15. Scapulae of the gibbon, baboon and rhesus, natural size 90

.ACROMION cephalic J angle*

SPINOUS PROCESS CORACOID PROCESS

GLENOID SUPRASPINOUS CAVITY FOSSA

VERTEBRAL MARGIN x AXILLARY \ % MARGIN \ L \ INFRASPINOUS FOSSA CHIMPANZEE

INFERIOR ANGLE

Plate 16* Scapulae of the chimpanzee and man, reduced to one-half natural size* 91

Plate 17. Top, ventral surface of the le f t scapula. Bottom, dorsal surface of the le f t scapula, a, human; b, chimpanzee, adult male; c, chimpanzee, immature male; d, gibbon; e, rhesus; f , baboon. 92

Plate 18. Left humeri of adult primates, a, human; b, chimpanzee; c, gibbon; d, baboon; e, rhesus. BABOON MAN

Plate 19• The trunk skeleton reduced to the same to ta l length in four primates (adapted from Schultz, 1950: I4I). iS 9h

SCAPULA

■GLENOID CAVITY

^ C L A V IC L E RHESUS

STERNUM

SCAPULA

GLENOID CAVITY

CL AVICLE

STERNUM

Plate 20. Superior view of thorax and left shoulder girdle in an adult rhesus and man (after Schultz, 1950:U2)e 95 Chapter Sjjc . Oomparative Myology and Function ■

The ttsefxilness of the coaparatlTe anatomical method has been considerably decreased by many workers studying the primates because they have failed to recognize the true historical developmental state of the animals being compared* We have to regard all the living primates as the end products of a long, involved evolutionary process* As Simpson has so aptly expressed the matter,, ’’no one can be ancestral to his grandfather^ (Simpsons 1950: 55)« Thus, statements which imply that man passed.through an evolutionary stage resembling that of the current great apes or the Old World monkeys should be studiously avoided*

. * ■ ' - Yet this type of implication can be found in much of the literature of comparative primate anatomy* - : . It must be kept in mind that there are undoubtedly structural features in the liv in g primates which were never found in any of their immediate ancestors., and certainly there, were characteristics in the fo ssil primates which are no longer represented in any member of the living species of primates0 ..-Therefore, i t is extremely risky to . interpret muscular variations as representing this or that primitive condition* Such interpretations have been the basis for much phylo­

genetic comparison and have led such men. as Wood Jones and Keith down some very devious byways® Comparative anatomical studies are of value i f a broad view of h istorical development be kept in mind* There are d efin ite homologous structures whose differences in closely allied species can be explained.

on the basis of functional adaptation. It is tempting to regard-the loss of an anatomical structure as. the result of an adaptation to a new situ ation 0. Howeverj, i t must be remembered that the . p ossib ility- ; exists that the structure may never have: existed in the forebears of :

that particular animal^:/'' v ; " .V: " : ; ; i - r' ; • - 1 It is unfortunate- that we do not .know more concerning the genetics of muscular variation0 There,are many variants of infrequent qecurance among, one of ;the other -of the primates isrhicb are represented by fu ll ; ' fledged anatomical structures.in certain :other members of the orders : I f the nature of the inheritance or perhaps development of . these variations were more fu lly known^. i t might possibly throw some lig h t upon phylo­ genetic relationships between different specieso • .. In the discussion ofthe following muscles5 emphasis on phylo- gentical sequence or so-called evolutionary development has been kept: ' - at a minimuyw •, It i s not : intended’ to convey any suggestion that man

developed from a chimpanzee-like or gibbono'id ancestor<, Instead, the emphasis has been.placed on the changes in functional adaptation as related to.the, differing -structure of particular muscles0 That there .

:are:;differences in the. origin:^ and insertion of muscles between allied •: species cannot be disputed* Howevers what these differences imply in the: way of functional interpretation may be largely a matter bf opinion.

As Washburn has pointed out,,' i t would be possible to experimentally verify,the effect of different:muscle placement upon the range of action : at ahy/particular, jbint ^ should be dones and undoubtedly will be ^ accomplished someday:(Waehbuin, 1950s 73)« ' ■ Because"function of the muscles is closely allied to the ambulatory

habits of the particular- animal,, a b rief '.'description of some. features of locomotion are given« ; - Both the rhesus and the baboon can be ' described as quadrupeds^, " although- somewhat modified and advanced over the terrestria l quadrupeds,. The. .rhesus ;is as much at home on the ground as it is in the -trees5 but the baboon is definitely restricted to a terrestrial habitat 0 - ;-The rhesus .y V t /.: : ' / " :: ' i : - ' . . - V . - : has been, observed to braohiate, that is progress by swinging from the armsg but this is not the consistent mode of progression. . The .forelimb is equally as important in quadrupedal locomotion as

is the /hindlimb. The direction of the -movement; of the am in locomotion is . forward-and baclhirardo ' ' This motion is somewhat restricted to these

directions because of the narrow thorax and vent rally directed glenoid cavity of the scapula. In addition, the short length- of the vertebral border restricts motion scmewhat.Medial rotation of the:..humerus, is

slightly more important thah is lateral or qutwgrd rotation. Both of these animals have a much wider -range of movement of the forelimb than do such terrestrial' quadrupeds as the dog or cat. This is perhaps associated with the grasping and manipulative.functions of the:forearm

. and hand. ;. '. . - . ' z ' The'gibbon is the most agile' and consistent brachiator to all - . the anthropoid apes. Studies on the locomotor habits of th is animal in " , the wild indicate that about ninety percent of the progression ds by ' f. brachiationo The remaining ;ten percent - is generally described a s■some form of .bipedal or quadrupedal walking.. . ■ ; There are several good descriptions of gibbon locomotion^ most 98 of them based on the work of Carpenters as is, for example, the following quotation from Hd'oton* . . #The fundamental motion in brachiation is ' ■ : . that of a swinging pendulum« When the -animal stops braohiating it oscillates before coming to rests A gibbon rises from a seated position on a limb, begins dropping to one side of the branch, extending the am and hand" nearest, the branch and then glides smoothly down­ ward and forward, cheeking the glide at its bottom by grasping the limb with its fingers and establishing the fulcrum for the first half of the swing® fhe. radius of the arc is about the equal of two-thirds of the length of the gibbon’s arm0 As the gibbon swings down, it contracts, its arm muscles, raising its body up nearer the branche Then the free arm and hand are brought round to grasp the branch in a second contact three or four feet beyond the f ir s t grasp* This movement involves a high degree of rotation Of the arm at the shoulder joint, and the second grasp may not be taken for an instant after the first is loosened^ At the second contact the grasping arm is flexed, so that the animal is pulled forward by it and by momentum® In the second swing the body of the animal does not go quite so far below the support® In the swing the leg s are drawn up toward the bodyvoeo When walking on the ground, the young gibbon may use both arms and leg s, or may hop through the arms using them as crutches®" (I9k2$" Iit8-lit9) It is frequently stated that the gibbon is intermediate in structure between the monkeys and the apes* This i s perhaps an assump­ tion which i s incorrect, being based, again, on orthogenetic reasoning® The gibbon possesses many very highly specialized features which are

undoubtedly related to its mode of progression® Such adaptations are the lack of a coracoid process attachment for the short head of the biceps, the peculiar mode of insertion of the m* peetoralis major, and

the fusion between the tendon of mG dorsoepitrochlearis and the intermuscular septum®

The thorax of the gibbon is widened laterally and the scapula lies on the back, with the glenoid cavity directed laterally® There 99 is much more freedom of movement of the upper limb than in the monkeys o The increase in width of the vertebral border and - the wide extent of " attachment; of the muscles along th is i margin are ' :: /adaptations for a direct pull upon the": shoulder such as occurs in : •, ' . . . v brachiatiori, ' v; : ^v.' ' ; ^ v' : ■ . - bp/v ^ . b: ' ' 1 "bb"", ''' ibl/bb, Vbb;bb:b-v.b:--b; ■ -'b:/ b ' The chimpanzee is not as specialized for brachiation as is the gibbon® " No figures' have been given for the relative importance; of brachiation over semi-quadrupedal locomotion® The best field study on i the, habits of the- chimpanzee ' has.been done by Henry Nissen of Tale . University® ' _ : b 1 " ■ . "An exceptional kind of walkings- apparently used when a chimp is going up or down h ill, is a crutch gait , ■ in which the; weight is borne upon the forelimbs and the - b hind limbs' are swung together between them. The usual gait on the ground is a slow walk Or .various forms of b_ running and leaping® Both in walking and in running the animal moves in a slightly sidling" fashion (i 0e»l ;;• the main axis of the body is at an" angle with the line- of. progression), In the quadrupedal gait on the ground the present writer has noted that, chimpanzees rest on the knuckles of th eir handss but sometimes the knuckles are ■ b directed forward, and sometimes outward® The toes are usually semi-flexed.with the exception of the great toe, -- which is thrust inward, at a wide angle® Chimpanzees - - n "never walk upon the knuckles of their toes so far as . .1 have observed. Nissen is of the opinion that chimpan-" zees can move faster than men "over :Unevenb-Tmde b . - covered ground. The run of the chimpanzee is a sort of lope of canter; not Very fast.accordihg:to what I have . seen. ■ These apes can walk up a tree without d iffic u lty , : even when the trunk is"four or five feet in diameter® They usually back down, but bNissen' says that they -may . come down head-first if the tree is one of 'small diameter.- . The. more usual; W a y of descending to the /ground, i f . th e ,; b - tree has low-lying branches, is to walk but to the end of a branch until it bends down with the weight of the b ahimal,, ,so - that .he . oan step off or hahgbby h is arms " and make■a straight drop. • Nissen notes that chimpanzees do ■ not ordinarily travel for any great distance through. -I. the trees. . %ey .get down- and walk :on the. ground. bn Nissen- has seen chimpanzees occasionally traveling from

Unw. of Arizona Library. one tree to another for short distances 0 The jumps are outward, and downward* the animal fir s t swinging . . . hy the arms and then letting go at the end of a forward swing* .l.have had opportunity to watch the chimpanzee arm-swinging or brachiating in the cages at Orange Park* Usually the progression from one part of the cage ceiling to another is achieved by alternate arm swings* performed very smoothly with f u ll advantage taken of perfect rhythm and momentum.* The horizontal movements seem to be performed more by body swing and thrust than by am pull*'* (Hooten* . 191^21 1 3 -llt)'./ .' . ; : ; ' ' ; ' ' The width of the thorax i s much greater in the chimpanzee than in the gibbon * There is also an increase in the relative massiveness of the musculature of the shoulder and the upper arm* The deltoid is conspicuously heavier in the chimpanzee* It i s reasonable to suppose that this increase in size of the muscles is related to the relative increase in the weight of the animal* . It is well-known that the chimpanzee has tremendous strength* and the'animal can hang suspended for great lengths of time by one arm*

The arms and shoulder girdle in man have been relieved of loco­ motor functions* except in the very young» How much of man’s orthograde locomotion is due to learning and how much is the result of inherent nuero-muscnlar coordination has-not been experimentally determined® However* it is interesting that reports, on feral children seem to indicate that they progress in a semi-quadrupedal mannerc This may indicate that* in the absence of contact with other bipeds* learning to walk upright is retarded* -. Unfortunately our knowledge of these feral children is* at best* fragmentary and there is little or no way of experimentally verifying these observations®

Movements of the arm in man are infinitely intricate*The greater 101 mobility andrangeof movement in the.forelimb is to some extent • ■

to the gz^GB'b©!"1 ©^fxGiGtxcy of til© H 6 c 1b ir©ls.tipnshi.p ©

Movements of the arm are intimately connected with movements of the scapula. Fop example5 '.when the arm i s extended forward, as in a hand shake<, the scapula moves forward on the la tera l chest w all5 or - when the arm; is raised"as in reaching- for a high shelf5 the inferior . angle of the scapula is . rotated lateralward and the glenoid cavity faces'upward, ,■ The analysis of a ll th e'd ifferen t functions is enormously fq.omplexj 'therefore5 only a couple of examples are given9 . . . ;.

f M« Trapezitis (Plate 8) - t ' : . r : • : : ^ This i s a very constant muscle in the primateSs exhibiting, only minor differences between the various forms« It is 'd iffic u lt to per- . ' : c eive a g eneral developmental trend ih ;. the Origin and insertion of th is - muscle as .related; to functiono. ' ■ t f - ; :

There-are; minor differences in the extent of the thoracic origin^ the lowest being in the gibbon, where- the muscle arises by means of an aponuerosis from the 13th thoracic vertebra. The.muscle normally arises ‘ from the 7th cervical to the 12th thoracic spine in raana ' The highest thoracic origin (from the 10th thoracic vertebra) is to be observed in the chimpanzee- and rhesus = Ih many th e chimpanzees baboon$ and rhesus^

an origin from the medial end of the superior nuchal line, and' Occipital protuberance is normalo .An occipital origin was completely lacking in • C the gibbon. Miller reports s' slight occipital origin for this form

(Millers 19328 9)s although. Stewart reports a cervical origin more in

' . accordance with my observations (Stewarts 1936: I 8I4) , Thusj ,i t seems ; / ; ■ . i p- p; v i’ - ' ; , V ' that the 'presence of an ocdipital origin of the trapezius;in gibbons is 102 quite variableo It is perhaps significant that this fora has the lowest thoracic origin as well* The chimpanzee and, the gibbon possess the most extensive clavicu­ lar attachments^ comprising at least the lateral half of the clavicle* Man is next in order with an insertion on about the lateral one-third of the clavicle* The rhesus possesses, the least extent of clavicular attachment* Attachment of the muscle on the spine of the scapula i s approximately the same dm all the forms under consideration* In all the forms studied, the muscle perfoims similar functions® Upon contraction of all the fibers of the muscles the scapula is drawn towards the vertebral column and because the cervical portion is ' larger and has a wider lateral insertion in the apes and ms/n;3 the inferior angle is rotated' somewhat lateralwardo Gontraotion of the upper fibers alone draws the phoulder cranialward and also rotates the scapula so that the inferior angle, points laterally* Contraction of the lower fibers alone draws the scapula towards the vertebral column; the shoulder caudalward and also rotates the inferior angle lateralwardo The middle and lower thoracic fibers also aid in fixation of the scapula*

Minor differences-is emphasis of ■..function probably occurs among the primates due to differeee®s in the sige of various parts of: the muscle and , as related t e altered axes d? the bony framework* The gibbon and man have the lowest thoracic origin of this muscle and un­

doubtedly use this with great frequency in fixation of the scapula* This would be especially important of the g:ibbon in brachiatio% for a 'fixed; stable shoulder girdle functions as the fulcrum between the lever :

arm and forearm and the weight of the body in movement through the trees* , ■ : . ■ ■ ' ' ■ - 103 , The deyelopmeBt ia .the chimpanzee and gibbon of the cervical portion of m„ trapezius as well as the increased width of the clav­ icular insertion is associated with the need for strong cranialward pull on the shoulder during brachiation® The thickness of this muscle . in the cervical region of the apes accounts for the stocky appearance of the neck and shoulderso " Lack of clavicular insertion is considered a progressive feature by some authors (Stewart^ 1936s 1801 ..Howell and Straus5 19331 120)0 A heavy clavicular insertion would seem to be a specialisation related to brachiatieno ' " v -. : . • Mo latissimus dors! (Plate 9) The mo latissimus dorsi shows a definite developmental trend in ■the primates*, reflected in an increase in extent of origin associated with specialization for brachiationo In the rhesus add the baboon^ the muscle arises from the spines of the lower thoracic and upper lumber vertebrae and the iumbodorsal fasciae This is veiy similar , to the condition which exists in the terrestrial quadrupeds such as the cato The gibbon exhibits a widen­ ing of the origin of the muscle to include the external surfaces of the last five ribs, where it interdigitates with the origin of m® external oblique abdominis<, The muscle reaches its greatest width of origin in man and the chimpanzee, where the muscle takes origin from the ilia c crest as well as the anterior surfaces of the last three or four ribs®

The extent' of the ilia c crest origin i s greater in the chimpanzee than in man® Also, man does not exhibit as great a lateral and anterior extint .of origin as observed in the gibbon and.the chimpanzees The most " ; ■ ' ■' : : :: ', :' : ■ . ■ : .... ' ' , 10k superior point of origiu •was found in the rhesus., (sixth thoracic vertebra)3 and. there seems to be a slight tendency for this point of origin to descend to the eighth or ninth thoracic vertebrae in the chimpanzee and man0 / Insertion upon the crest of the. lesser tuberosity of the humerus and into the intertubereular sulcus was approximately the same for a ll the forms o The tendon .of insertion was fused with the tendon of teres major in the gibbon (see also Stewarts 1936s 187)o Howell and Straus observed that the tendon of insertion of m0 latissimus dorsi in the

rhesus was splitj, one portion inserting with the me teres major tendon and the other inserting upon the crest of the minor tubercle and the intertubereular sulcus (Howell and Strauss 1933s 118)0 This condition was not observed in our specimen*. It is probable that fusion of the

tendons of m0 latissimus dorsi and teres major is a variable condition. Such fusion probably has little functional importance as both muscles exert approximately the same action on the humerusQ

Differences in the emphasis of function of the m. latissim us dorsi are to some extent due to the difference in the normal position of the arm in the animals under consideration^ The rhesus and the baboon are essen tially quadrupedss the baboon being especially adapted for terrestria l quadrupedismt, In a normal ambulatory position, the arms of these two animals are approximately at a right angle to the coronal plane of the body a The arms of the gibbon and chiiftpanzee are customarily extended over the head? or at rests pendant at the side in line with the coronal plane o The arms of man also are normally held at the side in line with the coronal planee 10$ The latissimus dorsi is the chief retractor of the arm in the rhesus and the baboon^ When the scapula is fixed, it rotates the arm some­ what mediallyo If the arm is fixed and the scapula free, then the • scapula is' rotated so that the inferior angle points medially and the scapula itse lf is moved somewhat eaudallyo For the gibbon and the chimpanzee th is i s an important muscle in brachiationo When the arms are raised over the head, grasping a branch, contraction of the muscle initiates elevation of - the trunkc If the trunk i s suspended by one arm only, then contraction of the muscle will rotate the trunk dorsalward as well o In man, as well as the chimpanzee and gibbon, i f the trunk i s fixed , the muscle w ill draw the

raised arm downward to the side and .rotate it medially<, With the arm fixed at the side, contraction draws the scapula medially and caudal- wardo ' ' It is generally accepted that the origin of m« latissimus from the iliac crest is a progressive feature, occuring only in man, gorilla (Haven, 1950s 1*0), chimpanzee and orang-utan (Stewart, 1936: 186)» A wide costal origin is also considered progressive, being lacking in the baboon and rhesuso The increase in the extent of origin of this muscle seems to be directly related to the need for strength associated with suspension from the arms as occurs in brachiation. Mo rhomboideus (Plate 9)

The sheet of muscle comprising the m= rhoboideus is quite variable in primateso I t may be composed of a major and minor portion as in man and the gibbon, or three portions as the rhesus and baboon, or i t may be a single undivided sheet as in the chimpanzee and the gorilla (Gregory, 1950s 2*0)o A ll of these variations can be found within any one of the ' ■ . . ■ 106 groups of higher primates3 though varying in frequency of occurance0 The mo trapesius. is normally composed of three separate., distinct slips in the rhesus and the baboon^ a condition also noted in such ter re str ia l quadrupeds as the cat • .(Beach* 1946$ 80)o The origin in the baboon as in the rhesus is more or less from the medial half of the superior nuchal line down to the seventh thoracic vertebra, along the dorsal midline <> The origin in man and the gibbon is quite - similar in that both normally possess major and minor portions® : The former „ .arises-from the spinous processes of the sixth and seventh cervical vertebrae and the latter arises from the first to the fifth or sixth thoracic vertebraeo The gibbon tends to have a slightly more caudal origin® The rhomboideus in the chimpanzee arises from the cervical midline up to about the level of the fourth cervical vertebra and ex­ tends down to the fourth thoracic« . : . ■ The angle of insertion of the fibers with the vertebral margin of the scapula tends to inopease from the rhesus to man® The tendency for; a more cranial origin of the muscle in the rhesus and the baboon makes the angle of insertion of the fibers with the vertebral border quite acute» In the man and 'the chimpanzee s the more caudal cervical and

thoracic origins increases this angle somewhat, while in the gibbon, ; the fibers of the muscle insert at almost a right angle with the verte­ bral border of the scapulao It is to be noted also that the greatest

extent of insertion along the .vertebral border of the scapula is to be found in the rhesus and the baboon, and the least extent of origin in man®. For a ll the forms the m® rhomboideus acts as an elevator and adductor

of the scapula, as well as a rotator of the inferior angle medialward® 107

.Howevers the possession of a slip from the superior nuchal line in the rhesus and the baboon aids the mc levator scapulae in cranial-ward movements of the scapulae Also5 the more acute angle of insertion of the fibers associated with cervical and occipital origins makes this muscle a strong medial rotator of. the scapulae This is a character of strong adaptive value in quadrupedal locomotion, for as the forelimb is retracted in walking, the inferior angle of the scapula is displaced medialward and the acromion is depressed* The baboon, which is much more of a terrestrial quadruped than the rhesus, has a stronger occipital origin and perhaps a slightly more acute angle of insertion with the vertebral border of the scapula* In the brachiators, the rhomboids tend to act in fixation of the scapula, while the arm remains mobile * A more transverse direction of the fibers is thus advantageouso Among the primates there is an apparent generalized trend towards reduction of the occipital and cervical origins as well as a reduction of the origin'from the lower thoracic spines =, Correlated with this is a slight tendency towards reduction in the extent of the insertion along the vertebral margin of the scapulae M* omocervicalis (Plate 9) This muscle is variously named levator claviculae, atlanto- clavicularis, atlantoscapularis anterior and omocervicalise Whatever it may be called, it is generally considered to be a derivative of the levator scapulae ~ serratus anterior muscle sheet whose insertion has migrated ; laterally * .

The origin of this muscle seems to be very constant, in all forms 108 except man, from the transverse process of the first cervical vertebra, anterior to the origin of m0-levator scapulae* When the muscle-is present in many it takes its origin from the first or second cervical vertebra; or lower* It is in the insertion of this muscle that a developmental trend can be observed* In the rhesus and the baboonj, the muscle fibers fan out from their point of origin to insert widely along the lateral half of the scapula spine and the acromion process* The muscle inserts along the superior border of the clavicle in the gibbon and the chimpanzee., extending more medially in the chimpanzee * The variant which occurs in man usually inserts along the clavicle or clavicular end of the acromion® The function of the muscle depends entirely upon its insertion* It moves the entire shoulder cranialward and rotates the' inferior angle

of -the scapula medialward in the rhesus and the baboon® In the gibbon and chimpanzeeg i t draws the clavicle and through i t the shoulder cranial” ward® Because the muscle is not directly attached to the scapula in these formsg it could not function as an efficient rotator of the inferior angle medialward* Most of the normal functions of th is muscle are taken over in man by the cranial fibers of m» trapezius®

The origin of m* omocervicalis remains constant in a ll formss hut there appears to he a developmental trend in the position of the insertion* In the lower forms it is upon the spine of the ,scapula and the acromion*• In the brachiators'it is attached to the lateral half of the clavicle medial to the. acromioclavicular joint® The variant which occurs in man is sometimes attached to the extreme la tera l end of the

clavicle or clavicular end of the acromion* This condition is apparently . 109 Intermediate between the apes' and the monkeysV M0 levator scapulae (Plate 9) The m* levator scapulae is extremely variable in the extent of i t s origin among the primates* It may be composed of from one to four slips of varying degrees of separateness^ arising from the transverse processes of the upper cervical vertebraeo The mm,, levator scapulae

and serratus anterior are two differentiated parts of a muscle which is a continuous sheet. in certain of the lower mammals 0 This latter condi­ tion apparently also occurs among certain of the primates such as the lemurs and perhaps the baboon (H iller, 1931$ 1 0 -li)* This muscle is called the m». atlantoscapularis posterior in the rhesus and is usually represented, by a single slip arising from the •

transverse process of the fdrst cervical.vertebra* In the baboon a similar muscle was observed which, however, arose from the first two cervical vertebrae, a condition not uncommon in the rhesuso This

latter muscle was separable from the nw serratus anterior in that it inserted on the dorsal surface of the vertebral margin of the scapula» For the gibbon and the chimpanzee th is muscle'was clearly separated from the m<* serratus anterior by a d efin ite interval* In the gibbon it arises by three or five separate slips (Stewart, 1936$ 188)| in the chimpanzee and man it usually arises by four slips® The interval separatin

the two muscles is slig h tly greater'in man than in the great apes* Insertion is invariably upon the dorsal surface of the vertebral margin opposite the supraspinous fossa® The width of the insertion is •to some extent related to the length of the vertebral margin above the root of the scapula spine 0 Thus man and the chimpanzee have wider 110 relative insertions due tottie increased width of the supraspinous fossae The degree of separateness of the various slips also seems to be extremely variable0 In nan the slips are usually fused before insertions but may be separate for their entire extent a The function of the Mo levator scapulae is to draw the scapula

. :■ . ■ : : : , / ' ■ ■■■ , ■ ; cranialward'and rotate it so that the inferior angle points medially@ Ifhen the scapula is held fixeds contraction of the fibers bends the cervical portion of the spine and.rotates i t somewhat toward the same hideo. 'p ' ' ' ': ' 'h, \ f : .Differences in the function of this muscle are directly related to the relative size of the muscle as reflected in the width of the origin and insertion* It is a relatively slight muscle in the rhesus and baboon3 and thus is probably a weak rotator and cranialward mover of the scapula* In both these functions it is undoubtedly assisted by the pars e&pitiss of the m0 rhomboideus* I t i s interesting to note that th is muscle is stronger in,those forms which lack a pars ca p itis element in- the rhomboid complex* In the brachiat ors this muscle is short and heavy and probably is assisted in rotating the scapula by the m* rhomboideus* . • There is an increasing degree of separation between the m* levator scapulae and the m* serratms anterior from the lower primates up to man® •Correlated with th is is an increase in the number of cervical vertebrae from which the slips take their origin3 as well as a greater tendency for • fusion of the various slips toward insertion* f

M® pectoralis major (Plate 6)

The pectoralis major muscle exhibits a great deal of diversity among the primatess but a generalized developmental trend can be discerned 111. in the widening of the origin^ It is considered along with the ami« pectoral is minor, pectoralis abdominalis and subclavius to be part of the primative ventral musculature of the upper extremity that has migrated onto the thorax (Howell and Straus, 1933$ 101)® The rhesus and the baboon possess approximately the same extent of origin for the pectoralis- major muscle® In these forms the muscle is divided into two portions on the basis of origins The two portions are separable to a variable degree® The pars eapsularls arises from

the capsule of the sternoclavicular; j oint and - the body of ttie mantibi?iugi, while the pars sternalis arises from the midline of the sternum for it s entire lengtho The baboon, however, has an additional extent of origin from the costal cartilage of the eighth rib lateral to the sternum for a few centimeters® Miller reports no capsular origin for the baboon, but it was definitely present in the current specimen (Miller, 1932s 13)= The fibers of the muscle meet across the midline for most of the extent or origin® .

In the gibbon the muscle reaches its greatest-vidth of origin ■arising from the medial two-®thirds of th e cla v icle, the sternum and from the costal-cartilages of the fifth to eighth ribs® A separate digitation also" arose from the anterior borders of the eighth and ninth ribs, la tera l to the rest of the muscle mass. This slip merges with the rest of the muscle immediately and.is definitely not a separate pectoralis abdominalis® There is a d efin ite separation between, the muscles of the two sides for the entire extent of origin®

Man and the chimpanzee possess almost the same width of origin for

this muscle.® It arises from the medial half of the clavicle, the sternum and around onto the costal cartilages of the ribs down as far as the /level of the sixth rib in man and the seventh in the chimpanzee<, The Y muscle also takes some of. its origin from:the.external abdominal, fascia* 1Y" Y She/insertion i s gene:i^ in a ll forms <, Usua-lly at : least the larger:portion of the tendon of insertion is hppnuthe crest of

.the major' tubercle of the humerus * The tendon of insertion is split in the rhesus • and the baboon,, a larger tendon inserts normally on the crest Y: Y " r^YY'--' ;/■•■" ' ' vY a-;.■ ■■ . . : ' Y/,-' ■ ' '/ of the major tubercle in both animals® However,, in the rhesus a smaller • tendoh, coming mostly- from the;■ caudal fibers of the muscle, inserts ; separately upon the humeruSo : In the baboon this sm ller tendon is fused

with the tendon , of .insertion/of the mv .pectpralis abdomihalis*; Y • The gibbon presents a complex .picture of insertion alsos ands ■ / unfortunately, the available .literature does not clarify the situation anyo In the present specimen^ the tendon split near insertion sending • the larger leaf.to insert along, the crest of the major tubercle and

; fusing > laterally • sqmeMhat with the m* deltoideuso . The smaller leaf inserted .upon the short, head of Yhe in0 biceps^ which in th is animal ';y Y;.Y y Yy V: ';:‘-d:':,c/b /-';tp- d h i , /!.-/;/.//:b''.://:/'b YY--.-I::: " ; arises from the humeral shaft o An en tirely comparable situation was

Observed by Stewart# but unfortunately he refrains from discussing the ;

.functional significance of this/insertion (Stewart5 1936s.162)0' Our dissections fa il to confirm the observation of Howell and Straus who . y ' .• ■ : . ■ /...;':Y/--;::,/: /:>•• jy-Y'd -.. yy .: - i :.Y.. record a yariation on this situation where the. tendon of the m0 pector- .a lis. mejor :inserted entirely upon the tendon,of the short head. ;' /; (humeral head) of the biceps without accessory attachmeht ■ to the'bone ■ /(lf3i: l5)» This latter situation' may well be a variation^ as '

•insertion of at least part of:the:;m;0 pectoralis major along the major . . "...,;y:./; :vy.. - V ;_ .113 tubercle of the hrmefub. seems"to be the rule throughout the:prlmit# T ' . ■ ■ : - v orders • ' : : ■ : , . The ihsertioh 'o# t the chimpanzee is con- . siderably simpler^ the tendon inserting along the crest of the major 't .-s

• ' ' . tuberclec, being partially fused laterally with the insertion of m0 ; deltoideus»: The chimpanzee, d iffers from.man. in having a continuouss ; "

undivided sheet-of muscle® ; - -- '' --- . . If-the f or elimb is raised .to the side " or over the head3 contraction of the muscle depresses the 'arin and rotates: i t somewhat medialward® '

When the arm'is pendant a t 'the sid e3 ' the .muscle acts as a medial rotator of the humeruso : When- an animal. is suspended by the arms3 the pectoralis major-: aids in raising the .thoramt In quadrupedal forms such as the . f '

rhesus and the- baboon3 the muscle functions in bringing the arm forward from a retracted: position3 functioning as the antagonist of m0 latissimus

I-. The. function of the muscle in the gibbon is especially complex • . due to the divided nature of the tendon of insertion® Undoubtedly,, the major function is as described above® However3 having the tendon insert

on the sho^t head of,the bleeps is. perhaps an adaptation favoring speed; by allowing the pectoralis major, to act through the biceps as a flexor of the entire -arm® The importance of this is debatable and until we know more definitely the Usual insertion^ further functional interpretations a,re speculative® .. ; 'V.-p. ; - ' : - . ■ -

:The widening of the origin of the pectoralis major to include the costal cartilages3 the ribs3" and the medial end of the Clavicle is one of i- the asignifibant'- traits characteristic of the braehiating apes and man®■ - Mo pectoralis minor (Plate 7) This muscle is considered to be a derivative of the entopectoral • layer of the common pectoral muscle mass of the lower vertebrates» There are a number of functional adaptations apparent in th is muscle among the primates9 involving both the origin and insertion0 The baboon and the rhesus both possess a wide sternal attachment for the origin of the pectoralis minors in addition^ the muscle takes accessory attachments from the fourth to the sixth costal cartilageso However; the origin in both the anthropoid apes and man does not ■ normally extend medially to the sternum* The muscle in. the chimpanzee; gibbon; and man normally arises, from the second to the fourth or fifth ribs9 usually being somewhat less extensive among the braehiators than in man0 . The insertion of the pectoralis minor in the rhesus is upon a broad aponuerosis which is continuous below, with the tendon of ma pectoralis abdominalis« In the baboon the insertion is mainly upon the capsule of the shoulder joint and the coracoacromial ligament; as well as upon the coracoid process itself» The chimpanzee is an exception among the braehiators in not possessing a coracoid process insertion for this muscleo Instead; the insertion is upon the. shoulder joint capsule and the coracoacromial ligament* The gibbon and man both possess strong coracoid process insertions and rela tiv ely weak capsular attachments^ The differences in width of origin probably affect the strength of the muscle more than its function* Thus the muscle is probably relatively stronger in the rhesus and the baboon than in the higher primates c There seems to be some correlation between the lateral migration of the origin • of the muscle and insertion upon the coracoid processo A more laterally, situated muscle “would permit a more direct eaudalward p u ll on the coracoid process thus making the muscle a more efficient rotator of the scapula®

; Because its major attachment is upon the coracoid process in the gibbon, ' and man, the muscle mainly affects the" movement of the scapula, acting as a medialward and cranialward rotator of the scapula, as w ell as , drawing the la tera l angle of the. scapula ventralwardo In the chimpanzee and the " rhesus, the muscle , affects the whole of the -shoulder, acting as ‘ h a depressor and ventralward mover of the whole joint<, The muscle in the

rhesus also acts as a medial "rotator of the arm because of its attach- ment to the coimon pectoral aponuerosis&; : ' The variability in the insertion of this muscle in man, as well as

throughout the, primate order, clearly indicates, the lack of stability of ■ / this" structure^. ' i . -.: g - . y . - : ; pectoralis abdominalis (ELate S and 7)

;, This muscle appears mostly among the arboreal, quadrupedal primates. It occurs as a rare variant.in mam however, Howell and Straus do not . ■ regard the. pectoralis abdominalis of the.rhesus as homologous with th is ; variant - (Howell and Straus, 1933 s 10l|.)e . . ' . ' '. '

.'■-y. The. pectoralis abdominalis. is, normally found in both the rhesus and the baboon. It arises from the external abdominal fascia and Inserts . ' " ' ‘ ' - /y'y'y along the humerus, medial to the insertion o f m, pectoralis major. There -ites; no Clearly separable pectoralis abdominalis in either the gibbon or ' .-the. chimpanzee« However, M iller in^lies; tbdt such a muscle is common or at least occurs in both these forms. (Miller, 1932s 15), ' “ ^

: The presence of this muscle is hard to explain bn the basis of fynciion* Because of i t s wide insertion upon the humerusj,' i t m= ' • doxibtedl^r acibs as a medial- rotatpr of the upper arm as -well as aiding . the m* pectoralis m jor M drawing the arm forward:; th is may w ell be an adaptation of the monkeys related to quadrupedism0 However^ th is V

structure i s not found among the lower terrestria l quadrupeds0 h :: : : Mc subclavius (Elate 7) ' This muscle exhibits only very slight differences in origin and insertion among the primates and apparently no major differences in \ : v '

function^ , p 7. ;': '' : ' . The subclavius in a ll forms studied^ except the gibbon,, arose : ; -v from the f i r s t costal cartilage^ an origin from the f i r s t three costal cartilages for the. glbbony however5 Stewart8 s obser« vat ion of this muscle agrees with that reported for the current specimen" ■ ' - -'V ' ■ - \ "" , " / , (Miller 1932: 12| Stewarts 1936: l63)s ioes^from the .second costal eartilageo ■ - ■■ /. ' : : ..

. Insertion is. almost inyariably upon the. caudal border of the -\7 ' Glavloleg lateral to the middle of' the bone:« 7 - - 7 . 7 ' • ' ■ - : ; : The most - important functions, of this muscle are depression of the ". shoulder and holding the clavicle against "the sternum* M« serratus anterior (Plates 6 and 7) .7. . : 7f • ' - ■•'7'':- ’ The mm® serratus anterior and levator scapulae are two differ­ entiated parts of a muscle which is a continuous mass in lower primateso ; ■ 7 ■■■ 7'7'V '7 " ' v ■: - - ■; - . 7,: 7.;-' : ;:v .7 7 7 :.' ■/77 A general trend can be discerned in the reduction of the lower cervical ~ v origin, of the muscle in the catarrhine monkeys until among the anthropoid :( : apes and mans the cervical origin is lost altogether* The upper cervical

origin of the primative muscle mass is: retained as the au levator scapulae 117 and may also be represented in some forms by the su omocervicaliso Both the rhesus and the baboon retain a cervical origin for this ■ ' - ' : , ■ ' ^\'.d.i -d " ^ . v • muscle from the last four to six cervical Tertebraeo This cervical portion is usually continuous with the thoracic part of the muscle which extends down to the ninth or tenth rib3 arising by separate digitations from each rib® The portion of the muscle arising from the f i r s t two ribs is . usually separate from the rest of the muscle mass in the gibbons the chimpanzee and man® The rest of the thoracic portion extends down to the tw elfth rib in the chimpanzee and gibbon and to the eighth or ninth rib in man0 The muscle is quite variable in the number of digitations from which i t arises® In general; however$ there are more digitationss encompassing even the last rib; in the braehiatimg apes than in man® d . - . •

The width of the insertion along the vertebral border of the scapula increases both relatively and absolutely due to the lengthening of the cephalocaudal axis of the scapula from the lower to the higher primates#

The insertion; in both the rhesus and the baboon,, begins just caudal to the medial angle of the scapula and extends down the vertebral border to the inf erior angle# ' the two anthropoid apes and. man, . .the /• Insertion extends from the medial angle to the inferior angle along the vertebral borderj howevers in the chimpanzee and man, there is an additional area on the ventral surface of the two angles which increases the area of insertion for the muscle, especially"for the upper and lower thoracic' portions0

Muscle function i s generally complex in muscle lik e the serratus .. . - n 8 ■ anterior which have an extensive origin and in. which portions of the .. muscle can^^ act separately^ : ...... '; For the rhesus and the baboon the cervical portion moves the ■ ; scapula cranialwards the lower thoracic portion, moves i t caudalward and the middle thoracie fibers draw the scapula laterally ventraiwardo In addition the muscle holds the scapula against the .thoracic wall, and ■ acts as a, stabilizer© This latter function is undoubtedly of great; " : . value in quadrupedism® •: ' ‘ .. ;'■; .The gtabilizihgftuactieh i s :retained in.man^ the chimpanzee^ and the gibbon3 but as thecervical portion is no longer presents the

, muscle does not. function well as a cranialward mover of the scapbla© . ' p Instead the muscle becomes a more effective lateral rotator Of the - \ . ■ scapula in these forms., a-.function of great importance in raising the ■ L • /arm sideways and over the head© The importance of this function to . . ■ brachiators. is. .reflected in the increased thoracic attachments; of the ../ muscle in the gibbon and the chimpanzee® Of course, the increased attachment is;also related to the need for a stronger stabilization of ■ v- the scapula in those forms, which habitually hang or move suspended from ‘ .

^ arms. • ; . . . ■ . ; M0 deitoideus (Plates 6 and 8) . - . ■ ' The mm.» deltoideus and teres minor are. two separated muscles which primitively are part of the same muscle mass® In certain of' the lower .mammals the deltoid'is regularly divisible into several parts® Even / among, specific groups of primates there is great variability in this ' feature®' A separate cleidodeltoid,portion is of frequent occurance in

■ ■'man>- as is ; y r tia i ; separation of a ll three (portions of the muscle® The y comparative anatomy of .the deltoid and other muscles of the shoulder

among .the primates reveals only veiy. minor:differem 'y V : : " fhpre is a distinct separation^ at origin^ of the three parts of "

the deltoid in both the rhesus and the baboono . The.clavicular origin ;a ■of the musple is rela tiv ely larger in both these formss and does n o t' < extend laterally to the acromioclavicular joint<, • A strong cleidodeltoid ' :-:A i s generally found in those forms where a clavicular origin is lacking ./ ' for the m» pectoralis major0 ; Such.a trend can be distinguished in' the; - ■ ' primates for as the pectoralis major origin extends around onto: the ; medial end of the-clavicles as it does in the apes and raan^ there is ■ a corresponding decrease in the extent of the clavicular origin for the m6 deltoido The acromial and spinous origins for the deltoid in the rhesus and baboon are roughly sim ilar in extent®. ; ' ^ / The gibbon exhibited an 'interesting variation in origin for the.; - -A.'. •m0.deltoid* In addition to' the clavicular3 acromial and spinous portions^ there was a well-developed infraspinous part of the muscle which arose \ from the fascia infrahpinata. all the way to the vertebral border and. : inferior angle of the scapula* It is interesting to note that this form also has the shortest spinous process bn the scapula® Perhaps the strong inf raspinous portion ■' of the deltoid is functional .adaption re= lated to this reduction of the spinous process® Both the chimpanzee and man show; a similar configuration for th is muscle® There is perhaps a slightly larger or more massive muscle in : ^

the chdmipanzee5 especially considering the anterior and lateral portions® ■ Insertion of this muscle is approximately the same .for a ll forms®

The differences in the deltoid tuberosity where the bv deltoid in serts .'g ;■ g • 120

has been discussed in the sections on the humeruso Because the deltoid envelopes the shoulder^ i t performs the v ita l function in all forms of stabilising the joint and of preventing the humerus from overriding the glenoid ehvity* In the quadrupedal position the cleidodeltoid portion acts as a protractor or forward mover of the arm while the spinous portion aids

the latissimus dorsi in retraotiono The contraction of all the fibers is important in abduction of the arm, raising it sideways until the arm is in a horizontal position# All of the above-functions are retained in man and the apes| hew=» ever, there is a shift in emphasis® Abduction of the arm is-perhaps the most important function of the muscle, especially in the brachiators® The gibbon also has a more extensive attachment onto the infraspinous fascia,than is found in the other forms® When the clavicular and acromial portions act together, the arm is raised somewhat and brought forward® Action of the acromial and spinous portions raise the arm and carry i t dorsalward® M„ teres minor (Plate 10)

This muscle is a derivative of the m® deltoid even though in man

it is often more intimately associated with the m® infraspinatus® There is a tendency among the primates for the extent of origin- to increase along the axillary border, reaching its greatest width in man® Some of this increase is directly related to the increase in length of the axillary border associated with the lengthening of the cephalocaudal axis of the scapula® . ' '.

Insertion is commonly upon, the distal aspect of the greater tubercle of,; the humerus 0 The tendon of insertion is strongly adherent to the joint capsule- in all forms except the gibbon where the muscle inserted - by means of fleshy fiberso • ' For the quadrupedal formss such as the rhesus and the baboon9 the muscle acts as a retractor of the arm and with the m* infraspinatus as a lateral rotator of the humerus» In certain instances it also serves : to hold the head of the humerus against the glenoid cavity® All of these functions are retained in the anthropoid apes and &an9 with, little difference in emphasis/ except that retraction of the arm is not as important in these forms® teres major (Elate 10) The Bio teres major is a specialized derivative of the au latissimus dorsi which has become separated and takes its origin from the axillary border and inferior angle of the scapula® Various degrees of fusion of these two muscles are normally found among a ll the primates® The rhesus and the baboon have a specialized rectanguloid fossa on the caudal end of the axillary border of the scapula for one origin of this muscle0 The scapula of the gibbon also bears a similar fossas but not as well delineated as in the previous forms® In man and the chimpanzee the specialized area has been reduced even further even though the muscle has increased in mass® Much of the accessory origin ' of the muscle in these latter two forms is from, a large triangular area on the fascia infraspinata® The muscle attains the greatest relative size in the chimpanzee®

Insertion in all forms but the gibbon is along the crest of the minor tubercle of the humerusj, somewhat proximal to the insertion of the ra0 latissiraus dor si s There is fusion of the tendon of insertion mth that of sic latisslmus dorsi in the gibbon which appears to be a fairly constant feature (Stewart^ 1936s 18?j M iller5 1932s 16)» The more important fm ctioh of the mnscle in the quadrupedal forms lik e the rhesus and the bahoon i s in retraction of the arm® I f can also act as a raedialward rotator of the humerus5 being assisted in both these actions by m0 latisslmus dorsio The intimate association between the mm teres major and the latisslmus dorsi in the gibbon may be an adaptation- favoring speed of action® - There are sim ilar examples of fusion in ranch of the forearm musculature of this form* Generallys ' howevers fusion of. the teres major and the latisslm us dorsi is con=» sidered to simulate the primitive condition# The functions in man and the chimpanzee are sim ilar to those in /' : ■ . , ' • , ' , ' - ■- , -v. v ; ; the rhesus® ' Howevers it is probable that the muscle is used more frequently to bring the arm back towards the side from an extended position® ■ V. ' ' v - . - Mo supraspinatus (Plate. 10} _ Differences in the conformation of the m0 supra spinatus among the■ primates is distinctly correlated with the changes in the shape of the scapulae Probably the differences in the size of the muscle have 'caused the attendant changes in the shape of the supraspinous fossa rather than conversely (lfolfsoBs 1950$ 337)® Some of these changes are un= doubtedly due to differences in the functional emphasis of the muscle®

The muscle i s long and rectanguloid in the rhesus® In the baboon it is more triangular and relatively shorter and ihickero The two anthropoid apes and .man also have a triangular shaped muscles but due .to the' oblique angle of the scapula spine2 the extent of origin has increased a great d@al» " Insertion is upon the iaost proximal end of the major tubercle of the humerus in all the forms, and the tendon is usually adherent to the capsule of the shoulder joints Holding the head of the humerus against the glenoid cavity i s one of the major functions of this muscle in the rhesus and the baboons The muscle becomes of Increasing importance as an aid to the m* deltoideus in raising the arm horizontally to the side among the higher primates« It also aids in fixation of the shoulder joint during this abduction* Mo infraspinatus (Plate 10)- . The m0 infraspinatus, like the rru supraspinatns, evidences certain .. differences in configuration which are related to the changes in the shape of the infra spinous fossa * There i s a steady increase in the width of. the muscle at origin as compared to its length from.the ca t-, arrhine monkeys, to man, to the chimpanzee o f he muscle reaches- i t s greatest width in the chimpanzee because of the greater relative width of the infraspinous fossa in this fom0 '

The. tendinous insertion in a ll forms studied was upon the greater : tuberosity of the humerus between the insertion of the m* teres minor -

and the me :supraspinatuSo : . " ’ . ■ ■ - Besides aiding in fixation of the shoulder joint, the muscle also acts as a weak retractor of the arm and a lateralward rotator of the'

humerus*' This la tte r function is i t s most important action in manj the ?. muscle being able to effeet rotation of the humerus through f0°4

Essentially, however, the muscle differs very little among the primates* sub scapular is (Plate 11) , The structure of the m„: subscapular is is basically the same in 1 , ; \ //-y" -; P "/'C '' /rr r '-yy ' : a l l : the, priniates«, •.Its' shape i s again'closely governed by the shape of ■ :;1-’ : ^ .t' '.',.y •'''." .'.yy.-yt ■t t - u ■-y.y.t • - ' ■ ■ :--'-yf,y . , • yyy ■; ' •..t ■ . the subscapular fossae Thus the muscle shows a progressive widening;; •;. '/ from' the lower ..to higher primates consistent- with the increase in

.. length - of the cephalocaudal axis of the scapula 6. . ' ' y ' The lack of significant function changes in the mm=.subscapularis,- • supraspinatus, and infraspinatus is probably related to the fact that the form of the shoulder girdle was established early in the primates and : 1 t changed only .-within narrow lim its^ . ' " .y ;

. y.. y Insertion of the muscle upon the whole of the lesser tubercle of . y. ;

• the humerus is almost invariably‘found.in all the primates». ; ' 1 ' The muscle functions as a medial rotator of the humerus and aids in fixing of the shoulder jointo The importance of these two functions

varies slightly for different forms0 Thus in the rhesus and the baboon t fixation is probably more important, but in man and apes, because of . the increased size of the muscle and the position of the humerus with ‘ .y respect to.the scapula, it acts more efficiently as a. medialwafd rotator - of the arm. y ; ; ■ ' y";'.' -.'V ''i :fy'...v yfy- ': y.. ;y>y : ' y," y ■" M® coracobrachialis. (Plate 12) : - ; y .. yyj

The m0 coracobrachialis is considered to have been composed. ' ' ; primitively of three distinct parts which have been termed super- .ficialis,, medius, and profundus,. The first of these portions occurs y: only as a,rare variant among the primates :(Howell and Straus, 1931s 22) ■' The. medius and profundus divisions .are found in both the baboon and the : rhesus* Usually only the medius is found among; the brachiating apes ; yy: 125 mans although a profundus element may occur as an inconstant variant in these animals as wells - The profundus portion in both the baboon and the rhesus arises from the deep surface of the common coracoid tendon and partially from ' the coracoid process itself» The muscle is extremely short and inserts upon the surgical neck of the humerus proximal to the tendon of insertion of mo teres major* The medius, which arises from the tip of the coracoid process in common with the m* - biceps in a ll forms except the gibbon $ is the larger muscle® There are differences in the size of the muscle,, but it is difficult to determine whether the increase in size from the rhesus to man is iruely relative or merely a reflection of the increase in size of the animal* The muscle is heaviest in man* As the short head of biceps does not arise from the caraeoid process in the gibbon? there is no common origin with m0 coracobrachialis in this form® Insertion of the coracobracMalis was along the medial aspect of the shaft of the humerus in. all the animals examined in the current project® The insertion was entirely fleshy in both the rhesus and the baboon® However? in the gibbon there was accessory insertion, by ten­ dinous as w ell as flesh y fibers® In the chimpanzee insertion was by means of a short aponuerosis along the'humerus® Insertion in mqn is normally by a flattened tendon®

The profundus portion is undbubtedly of value to the quadrupedal forms in fixation of the head of the humeruse It can also act as a mdlalward rotator. of the upper arm? although not strongly® In many respects the muscle functions as a fleshy reinforcement for the proximal and la tera l aspects of the join t capsule® 126

The longer medius portion serves as a protractor of the arm in the rhesus and baboon® The corresponding muscle in the gibbon* chimp* and man acts as a flexor of the humerus at the shoulder as well as an adductor of the arm0 The increase in strength of action* as evidenced by the possession of a tendinous insertion in man and sometimes in the chimpanzee* i s interesting® Perhaps th is i s correlated with the in­ creased weight of these forms® Certainly flexion is a more important function of the muscle in man® ' . , Ho biceps brachii (Plate 12) The m* biceps brachii in the primates normally has two heads of origin» The long head is the more constant structure in all forms© The short head exhibits numerous variations in regard to origin as well as i t s relationships to other muscles®

The short head of the biceps arises from, the superficial, layers of the common coracoid tendon in both the rhesus and the baboon® It is interesting that the origin of the short head in the gibbon i s from the proximal end of the humerus® This condition i s apparently normal® (Howell and Straus* 1931°. lh$ Miller* 1932s 19)© The coracoid origin in man and the chimpanzee i s by means of a wide* stout tendon®

The long head arises from the supraglenoid tuberosity in a ll the forms under discussion0 The tendon is straplike as it passes through the bicipital groove in the rhesus and the baboon© In the anthropoid apes and man the tendon is rounded* conforming to the shape of the groove except at the point of . origin where it becomes ovoid® Fusion of the two heads occurs at about halfway down the -arm in the rhesus* baboon* chimpanzee and man® The short head blends with the ■ .... , • 1 2 7 remaining part of the muscle almost immediately in the gibbon (see also the discussion of m0 pectoralis major for details concerning the origin •of the short head, of m0. biceps) e ' . Insertion is by means of a stout tendon upon the radial tuberosity- in all forms examined^ Eo lacertus fibrosus was observed in the rhesuso Howeverg a fa sc ia l condensation which approximated a lacertus was present in the baboon and the gibbons A well defined lacertus fibrosus was observed in the chimpanzee = A wide flesh y band, composed mostly of

' .'■■■ ■: ' : -■ - v : V ' fibers from the short head of the bieepss passed down the aim to insert widely upon the ima.? pronator teres and flexor carpi radiatus in the gibbon,, Such an insertion allows the short head of the muscle to act upon the f oreaim as though i t were one long muscle extending the length of the am o The.biceps act as a flexor of the arm at the elbow and as the strongest la tera l rotator of the forearm in the rhesusj, baboon, gibbon, chimpanzee, and mano Both heads working together fle x the am at the shoulder as w ell as rotate the humerus medialward in a ll forms except the gibbon* In th is la tte r animal the muscle i s d efin itely a stronger and more important flexor of the forearm, and medial rotation, of the . humerus is not possible because of the lack of an origin from the coracoid process* . ._

M* brachialis (Plate 12)

The m0 brachialis frequently arises by two heads in the primates, a situation which is considered to be a reflection of the primitive con­ dition of the muscle* Varying degrees of separation of the two heads may be observed in man and other primates* The muscle increases in mass 128

from the rhesus and the baboon to the anthropoid apes, with man occupying an intermediate position in this respect* The origin in both the rhesus and the baboon extended up the lateral side of the humerus to the Surgical neck<> lo such extent of origin was observed for the gibbon or the chimpanzee» In these forms : the origin extended only a few centimeters beyond the distal point of insertion of the m0 deltoid on either side. The muscle takes its origin ' from the anterior surface of the distal end of the humerus down to just

above the epicondyleso Insertion-is upon the ulna in the region of the coranoid process0 The tendon of insertion of the rhesus and the baboon i s narrow; that of the gibbon, chimpanzee, and man i s somewhat broader and heavier, ■

The brachiatis i s a pure flexor of the forearm in a ll the forms ; being considered. There may be considerable differences in the strength of action0 The massiveness of the brachialis among the brachiating apes

would tend to eonfim this views The increased size of the muscle is a reasonable adaptation among animals who use their forelimbs in loco- • motion as do the brachiator®

M* triceps brachii (Plate'll)

The m» triceps is a very.conservative muscle among the higher primates. Slight differences- ifi the extent of the origin of the long head and a relative decrease in the size of the muscle may be noted. The long head, which arises from the.axillary border of the scapula is fleshy and covers the lateral two-thirds of the margin beginning at the infraglenoid tuberosity in both the rhesus and the baboon, Howell

and Straus report that the long head arises from the lower half of the 129 axillary border in the rhesusc They must be referring to the ventral margin, of the lateral end of the axillary border because the long head does not arise from the medial end of the axillary border. The long head arises by a broad* flat tendon from the ventral surface, of the axillary margin in the gibbon and chimpanzee and in man* from the infraglenoid tubercle onlyo The extent of this origin is decreased*. but the corresponding strength has been, increased by tendinous attach” mento The la tera l head arises from the proximal end of the posterior surface of the humerusc The relationship between the long and lateral heads is intricate in the rhesus and baboon* and fusion between the two heads occurs almost immediately* Fusion, between the two heads does not occur until about one-third of the distance down the. humerus in the gibbon* and one-half the distance down the humerus in the chimpanzee and mane The increased separation of the two muscles is correlated with a greater range of action in the arm* _ .

The medial head has a more, extensive origin in the rhesus and baboon* le ss in the gibbon and chimpanzee* and lea st in man. It i s generally separable* almost tp insertion* in all forms® The decrease . in size of the m. triceps is more apparent in the medial head than any other. ' ^

All three heads join a common tendon of insertion which is attached to the olecranon process and to the superficial dorsal fascia of the forearm.

The triceps act as an extensor of the forearm at the elbow. The leverage is such that strength is sacrificed for speed in the rhesus* 130 ■fp baboonj chimpanzee, an.d mn-0 The long_ head also aid.s the mo latissinius

dorsi of the rhesus and baboon, in'- recovery* The long head, can act .as: - an adductor of the whole arm in the forms, ^ dorsoepitroohleafls (^ate 12) ■ - . " The ra0 dorsoepitrochlearis is a derivative of the m„ triceps which has .secondarily become attached to the tendon of insertion of the -

. too' latissimus dorsi = -: This muscle is normally ■, represented in man by a . fascial slip from the tendon of..m0 latissimus to the. long head of m0 ... ■ .. triceps' or to the dor sal brachial fasciae & d istin ct muscle i s ' OGoasionally observed in man*: : , : ■ ; : : In the rhesus, and perhaps in the. baboon, the muscle, normally ■ arises from the tendon or muscle b e lly of m„ latissim us '.dorsi*- There, was also accessory origin from the long.head of zm triceps in the,present ■ ; specimens of the baboon and the /cliimpanzee®■ The. muscle arose only from. ; - - the .tendon, of m0 latissimus dorsi in the rhesus<, This was not encountered. 3^. - dissectaon0 ..- ■ ■ ;■ ■ '-f■■ p-. : ' '

;)' -p :'The tendon of insertion; Of ‘ the muscle, in t heirhesus ■ - and' baboon' is p attached to the olecranon and then^passes into the dorsal forearm fascia® - ,

This-, c ondition was hot observed in the chimpanzee or the gibbon,,. However , :.: the tendon of insertion in the gibbon was fused with the medial inter­ muscular' septum along,its edge^; : The' short: head of me biceps;was also .'-v

partially fused with the medial intermuscular septum,, but it could not P p - be considered, as inserting- upon the tendon of nn dorsoepitrochlearis as reported by Howell and Straus (1931: 15)« The terminal point of .

attachment in both gibbon and-chimpanzee, was upon the pposterior aspect, of . the medial epicondyle^' \ : -- ,. ■ V '. .p;: - p - .

'P: - ; U l Because of its attachment upon the olecranon in the rhesus and baboon,) the m. dorsoepitrochearis acts as an extensor of the forearm in conjunction with the m0 tricep sa Howevers in the chimpanzee the muscle no longer has an insertion upon the forearm and/ therefore 5 can hot act as an extensor of this portiono Instead its action is limited to adduction of the arm and extension or dorsalward movement of the humerus upon the scapula® The function of th e: m® dorsoepitrochlearis in the gibbon depends upon interpretation of the mode of insertion® Howell and Straus regard the prime function of the muscle to be in preventing - !tthe biceps from springing forward unduly11 and thus weakening the action of the m® pectoralis major upon the short head (humeral head) of the iru biceps (Howell and Straus 5 1931:' l^)®, It is not too clear how a muscle acting in the same direction can prevent or inhibit, as would m® dorso­ epitrochlearis i f i t inserts as described by Howell and Straus5 the action of another muscle also acting in the same direction® If the muscle inserts upon the intramuscular septumas observed in the present case (see also Hiller3 1932s 22), then the function remains one of adduction and extension of the humerus at the shoulder® 132

Chapter Seren Summary and Conclusions

Summary Comparative dissections were made on two non-brachiating Old World monkeys and two brachiating anthropoid apes in an effort to determine the gross anatomical structure of the pectoral girdleo The development of the several theories of man's phylogeny have been briefly reviewed and an attempt has been made to indicate that a means ex ists whereby the two major conflicting views might be reconciled The forelimb and the pectoral girdle "in the lower primates5 such as the monkeys and,the brachiating apes3 is intimately associated.with locomotor functions =, There are numerous changes in the origin and insertion as well as the relative size of the various muscles i n ­ different primateso These.are definitely associated with the different functions which they are called upon to perform., Also associated with the changes in musculature are consistent variations in the nerve ■ supply as well as modifications of the bony framewcrko „In man the pectoral girdle has been freed of locomotor functions3 howevers it shares many structural features in common with the anthro-A

poid apes and retains the greater mobility of the. forelimb developed by the ancestral apes0

. - These pertinent facts justify the conclusion that3 in general* man resembles the African apes more than he does any other primates3 but it does not necessarily imply a brachiating ancestry for man* ■. . . 133 Conclusions It is doubtful if one- can come to a conclusion regarding the probably nature of the hypothetical ©ommon ancestor of man and the ■ higher primates on the basis of comparative anatomy aloheo Unfortun­ ately^ th is i s not lik e a correlation problem in s ta tis tic s where a regression line can be extended in either direction, to determine a known value0 Perhaps if. we knew more about the paleontology of the great apes and of the time factors involved in their rise and deploy™ ment5 then we might be able to make some reasonable conjectures concerning th eir immediate ancestors® I t may be that there were ten different species of gorilla and, chimpanzee in the Miocene^ of which we only have one or two surviving todayo We really do not know how many experiments nature performed before sh e.arrived at the four living anthropoid ape groups^ The idea that the common ancestor of man and the great apes was similar to the living gibbon has little or no basis in facto The gibbon is a highly specialized animal adapted to life in the trees and locomotion by braehiation0 However, does this mean that we have to rule out the possiblity of a brachiating progenitor for the line of man? If we observe the. structure of the pectoral girdle in apes and many we find many sim ilarities which are not necessarily common to the lower catarrhineso If there were some way to prove that these similarities were directly the result of brachiationy then the problem could be re solved c Man would be the descendant of a.brachiator®

How ever ^ no one has experimentally determined that there is a direct causal relationship between brachiation and the structure of the pectoral 13h girdle in the apes and maru However5, these sim ilarities can not be ascribed to or explained away on the basis of parallelism^ The baboon illustrates perfectly the adaptations which an arboreal quadruped raonkey makes to ground lin in g % He remains a quadrupeds retaining many of his arboreal monkey features while modifying others to better suit him to a terrestrial habitat® If man had sprung from a catarrhine monkey-like progenitors what.reason was there for him to have assumed upright bipedism? The dorsal position of the scapulae and the lateral broadening of the thorax in apes and man contribute to the increased mobility of the shoulder girdleo It may be argued that the assumption of upright posture in freeing the forelimbs from locomotor tasks also brought in its train increased range of action® There are. certainly great degrees of variation in the dependence on brachiation among the anthropoid apes® The gibbons progress almost exclusively by this methods whereas, the gorilla rarely does® The attainment of upright posture might have been an early anthropoid ape achievement with brachiation being a secondary adaptation to life in the trees® This does not imply any adherence to Straus * s catarrhine monkey theory for the origin of man, but only means to point out that until a causal relationship can.be proven between the whole inter-related sequence of muscular and sk eletal adaptations with brachiation, we can not definitely assign an am swinging-ancestry to'man® Conjectures concerning the ancestry of man which are based on comparative anatomy can only offer us the barest of outlines for his phylogeny* Anatomical studies have to be correlated with paleontological . ■ ; ' ■ - 135 studies9 they cannot • be the f in al answer = We have examples of fin e comparative anatomical studies undertaken by. different investigators which have arrived at diametrically opposed conclusions= The reason is that in each case emphasis was on certain comparative features to the exclusion of otherso 136

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1950 Editor* The anatomy of the gorilla® The Henry Cushler Raven Memorial Volume® Columbia University Press# New York® Hartman# Co G® and Straus# ¥* L®#Jr® , . 1933 The anatoifQr. Of the rhesus monkey® Baltimore# Md* Howell# Ae ’5®. and Straus# ¥® Le# Jr® 1931 The brachial flexor muscles in primates* Proceedings of the United States National Museum0 No* 29135 Vol® 80# Art o 13# 1—3I 0 . ' . 1933 The spinal nerves® In Hartman and Straus# The anatomy of the rhesus monkey# 1933 Huber# B0 1931 Evolution of facial musculature and facial expression* Baltimore# Md® - . Huxley# To 1863 Evidence as to 'man’s place in nature# Williams and Norgate# London® 137 Leachs ¥»l j® 1 v'' ; ‘ ■ - v :.. : : ; ' I 9I46 Functional anatomy of the mammals New Fork :M ller? :RB: 1932 Evolution of the; pectoral girdle and forelimb in the yy - -"1" .primate5= American Journal of Physical 'Anthropology5 ;.V,. ■ ,1. : \Tol«: 17: '1 a:": 193k Comparative studies upon the morphology and distribution ' v- of the brachial plexus 0 American Journal of Anatomy^ •:vl - Vol. 11+3-175. : ' J ; . ; p •'llv. . .- ' k,. :Mirarta He;.G^ ^ y "'i' P'; dl" 1:,;: - ' 1873 Man and apeso Robert Hardwicke5 London0 • . . i Horton^ :D.:-Ji::' ■> \ ^ . 192)4 Evolution of the human foot = I I « American Journal of ; : i V- - Physical Anthropology= Vole ?2 1-32. : dp V i : ' Eurieg J«, and Mivartj E@ 1 . ' : ' ' ; 'l l'’ " i ■ ■ . 1 I 872 v" i3n the iaiiatomy' o f: the lormBoidea^, ’ Transactions - of - the . - :v; : - p- Zoological Society, of London0 7 s 1“113® . : ■ ,1 . ' . ■■ 7-;

:p Osborn^ l 1 - 'll:! pkl' C $ 'i' 1 '1-/' 1 '1 / : x ' .' 19271 Recent ■ discoveries relating/-to the origin andlahtiquity of Id; ' • ' man0 Science5 63s I1.8l-j4.880 . 1 " ' ' ; '' : "'■’ ■./• 1 : i f ■ ; /. 1,-: i : /'i-i: i i i i , : - .. 'i:: 'ipipil-; ' .1 • -i.p. >■ . Roiaki o6;p .: v:;;:-,iip.p-p,:/-:l :.- /ip l i p :■ . .p't ,1/ z..- ,i-:d 1908 - Die anatomie des genus colubus. Verhandll Kon0 Ahade . - l -; ' Weto, Amsterdam, Vole Ik: 1. ' ‘ p, . " p - p:'Raveni: I® :G« 1 < -i;i l-;p- -l.p gd .,d. W :P -:dl'l Plpd ' ; i; p-l : pp'- d . 1930 Regional. anatomy ; of ;the. gorilla <> ; In Anatomy of the 1 ■p' '■; ;P p" 1' llgorillaV: edo WyK^ Gregoiy® . ;. -p 'p / : ;;1:: d; ■ -1 d;. '1;. l:Schuita5 A®;Hv ' W: pl:lPdW:p -iv"'' ip p: lpli;l ill'- ■■■■:p i ;'p. : : l ;d, 1930 The skeleton of the trunk and limbs of - higher primates« 1_ Idl'd il l d llHumh Biology, 2t 303-138. 1.. V ; 1 dp . ; .1 dvl d . 1936 Characters common to ■ higher primates and .characters ;■- ■ ;1 ; - pd sp ecific to man. Quarterly Review of Biology, T o ll 11, .1 Id . d'H'd'd;: v dd 'NoO.. 3 and-hi d' d 111' "d-d;, //.p - d ' ■ ■ ■■'■ -■ .1 : p p d dp' - I9h0 , Growth, and development. of the chimpanzee» Publications ■ : 1 ' pd .. . . ; d ■ of the . Carnegie . Iristitut e No s ' 325 c Contributions to I d ■ pp p dEmbryoiogy 29:-11-63,1 ' p. p.;- ' ■' l i i l 11 -p p-' -dl ; ■; ;d' 1950 The specializations of man . and. his place among the ' 1 d , . . - catarrhine primates. Cold Springs Harbor Symposium on d- ' Id - d-d Quantitative Biology, Vol 15: 37^53. -1 1 1

1' ; 1950a The physical distinction of mans Proceedings of the p p gd. ,, .American Philosophical' Society, -Vol0 9Ui i(.28-1191 d -:d 138 Simpson^ Goflo . ' .. ■ 1950 Some principles of historical biology bearing on human originso Gold Springs Harbor Symposium on. Quantitative . Biologyj, Vole l5s r. . V Sonntag.$ Go F ,. . 1923 On the anatomy^ physiology and pathology of the chimpanzeee Proceedings of Zoological Society of London« 323-i29o 192.U Morphology and evolution of the apes and man, London* „ Stewartg f* D0 . ' - 1936 The musculature of the anthropoids* I e Neck and trunk® American Journal of Physical Anthropology, Vol* 21, . No* 2, 114.1-20)4® Straus, ¥® L®, Jr® 1914.0 The posture of the great ape hand in locomotion and its philogentic Implications® American Journal of Physical Anthropology, XIFII, 199-207» 19141 The phylogeny of the human forearm extensors® Human Biology, J i l l , 23-50, 203- 238® 19142 Rudimentary d ig its in primates® Quarterly Review of • ' Biology, IVII, "228-21130 ' I9k9 The riddle of man’s ancestry® Quarterly Review of . Biology. 2I4.S 200-223® 1953 Primates® In Anthropology Today,, ed® A® L® Krdeber, 77-92® Ghicagp® . ' - Washburn,. S®' L® 1950 The analysis of primate evolution with particular reference to the origin of man® Gold Springs Harbor Symposium on Quantatative Biology® Vol® XV, 67-78® 1947 The relation' of the temporal; muscle to the form of the skull® Anatomical Record, 99 i 239-214.8 ® Waterman, H®. 0® - . 1929 Studies on the evolution of the pelvis of . man and the other Primates® Bulletin,. American Museum of Natural History® 58 s 585-61|.2o - - .

Wolf son, B®'A® .v: . • 1950 Scapula shape and muscle function with special reference to the vertebral border® American Journal of Physical . Anthropology, .n®s®, Vol6. 8, No® 3s 331-338® 139

Wood J.G>n6s> Fo ^ • • - ■ ' " ' - 1923 The ancestry of man. Gillies ,& Go.. Brisbane. , :wbdilards H. H< 1925 The anatongr of. the. tarsins spectrum. Proceedings of the Zoological Society of London0 7 : i071-ll8I|.®

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