II Thoracic Limb Chapter II Thoracic Limb 31 BONES - THORACIC LIMB II Thoracic Limb Locate the regions of the thoracic limb on an articulated limb. A • Thoracic limb: also called the 1. Shoulder region pectoral (PEK-toh-ral) limb or forelimb. 1. Shoulder region: area con- A. Scapula taining the scapula and hu- meral joint. 2. Brachium or arm: area con- B. Humerus taining the humerus. 3. Antebrachium or forearm: B area containing the ulna and 2. Brachium radius. or arm 4. Manus: area containing the carpal, metacarpal, digital, and sesamoid bones. II - 4a. Carpus: the structure made I up of carpal bones between the E. Interosseous space E forearm and metacarpus. D - 4b. Metacarpus: formed by 3. Antebrachium the metacarpal bones. C. Radius D. Ulna - 4c. Digital region: contains C the phalangeal bones. Med H. Accessory carpal bone Lat H F F. Carpal bones G. Radial carpal bone 4a. Carpus Dew claw I. Metacarpal bones 4. Manus J. Prox. phalanx I J 4b. Metacarpus M. Prox. sesamoid bones K. Middle phalanx K L. Dist. phalanx L 4c. Digits I, II. Bones, Right thoracic limb, lateral & medial views Review in general the bones of the thoracic limb using an carpus and digits in the metacarpus. articulated skeleton and individual bones. J. Proximal phalanx (P1): articulates with the metacarpal A. Scapula: the flat, triangular bone of the shoulder defining bone of the same number. the shoulder region. K. Middle phalanx (P2): the second bone of a digit. B. Humerus: the largest bone in the thoracic limb in the L. Distal phalanx (P3): the third bone of a digit. arm/brachium. M. Proximal sesamoid bones: two bones per weight bear- C. Radius: the weight-bearing bone of the ing digit on the palmar aspect of the metacarpophalangeal forearm/antebrachium. joint (one for the dew claw). D. Ulna: the long, thin bone of the forearm serving mainly N. dewclaw(II): first digit that doesn't bear weight. for muscle attachment and formation of the elbow joint. E. Interosseous space: the void between the ulna and ra- CLINICAL: dius. • Osteosarcoma: tumor of F. Carpal bones: the 2 rows of short bones making up the bone. It often metastasizes carpus. to the lungs; take chest radio- G. Radial carpal bone (II): located on the medial side of the graphs before any surgery. proximal row of carpal bones. • Physes/growth plates: all the physes of H. Accessory carpal bone: located on the lateral and palmar thoracic limb long bones close by 1 year sides of the proximal row of carpal bones. of age (except the proximal physis of the I. Metacarpals or metacarpal bones: the bones between the humerus (twelve to thirteen months). 32 II Thoracic Limb SCAPULA C D. Supraspinous fossa D B E B. Spine H C. Acromion F * * 3 2 G. Glenoid cavity 1* III. Left scapula, E. Infraspinous fossa ventral view 4 I. Left scapula, lateral view G 2* H. Supraglenoid 1* tubercle H F. Subscapular fossa II. Left scapula, * * Defined in legend (LPI: lower priority item) medial view G 3 Study the bones of the thoracic limb on an articulated 1. Scapular notch (I, II): the indention in the cranial border at the level of the neck where the suprascapular n. crosses skeleton and on individual bones. This will help you 2. ^Neck (I, II): the constricted part of the scapula joining the articular angle when dissecting the muscles to understand their to the rest of the scapula attachments and functions. 3. ^Coracoid process (kor-ah-koid) (II, III): the small process on the medial side Thoracic (shoulder, pectoral) girdle: consists of only of the supraglenoid tubercle for the attachment of the coracobrachialis m. 4. Serrated surface (II): the dorsal part of the costal surface for the attachment the two scapulae in the domestic species as they of the serratus ventralis m. usually lack clavicles. The limb is attached to the ^ More important (LPI) body by muscles (syssarcosis) and not by a conven- D. Supraspinous fossa (soo’-pra-SPY-nus) (I, III): the area cranial tional joint. to the scapular spine providing attachment for the supraspinatus A. CLAVICLE (KLAV-i-kul) (collar bone): absent m. or rudimentary (oval cartilaginous plate) in most E. Infraspinous fossa (I, III): the area caudal to the spine providing dogs. The cat and some large dogs have a clavicle, attachment for the infraspinatus m. which is a separate bone seen radiographically. It F. Subscapular fossa (II, III): most of the medial (costal) surface of doesn't articulate with the shoulder as in humans, the scapula providing attachment for the subscapular m. but is embedded in the brachiocephalic m. So the G. Glenoid cavity: the shallow cavity that articulates with the thoracic limbs are not spread laterally but are under head of the humerus to form the shoulder joint. the body as needed for four-legged motion. H. Supraglenoid tubercle: the process near the cranial glenoid B-H. SCAPULA (SCAP-yoo-lah) or shoulder blade: cavity, providing attachment for the biceps brachii m. he flat, triangular bone of the shoulder. • Scapular cartilage: the thin band of cartilage on the dorsal border B. Spine of the scapula (I, III)#: the long projection of the scapula in the dog that is lost when bones are prepared dividing the scapula’s lateral surface and ending (not shown). as the acromion. CLINICAL: C. Acromion (a-KROH-mee-on) (I, III): the expanded • Articular scapular fractures: requires accurate distal end of the spine of the scapula where the reduction and internal fixation or DJD# develops. deltoid m. arises. • Supraglenoid tubercle fracture: biceps # (Roman numeral) in parentheses after a structure indicate in which brachii m. origin. Treat: single lag screw or illustration it is labeled (often on facing pages). Absence indicates # Degenerative joint disease the structure is in all illustrations. tension ban. 33 HUMERUS II Thoracic Limb B B, C. Greater tubercle, E. Intertubercular (bicipital) groove D Point of shoulder A C, B 2* D. Lesser 1* tubercle F. Deltoid tuberosity A. Head II. Right humerus, proximal view 3* 3* 6* 5* I. Right humerus, I. Olecranon fossa cranial view G H 4* I 7* 7* III. Right humerus, distal view G H. Med. (flexor) H epicondyle G. Lat. (extensor) * * IV. Right humerus, * * epicondyle 6 5 5 6 G * Defined in legend caudal view G-I. Humeral condyle * Defined in legend (LPI) G-I Study the humerus on an articulated skeleton and on in- 1.^ Neck (collum) (IV): joins the head to the rest of the bone dividual bones. 2. Insertion of the infraspinous tendon (I) A-J. HUMERUS (HYOO-mer-us): the arm or brachial 3. ^Brachial (musculospiral, spiral) groove (I, IV): spirals from the caudal to the lateral to the cranial surface of the humerus carrying the bra- bone is the largest bone of the thoracic limb. It articulates chialis m. and radial n. proximally with the scapula, forming the shoulder joint, 4. Lateral supracondylar crest (I): passes proximally from the lateral and articulates distally with the radius and ulna, forming epicondyle and gives rise to the extensor carpi radialis m. the elbow joint. 5, 6. Articular surface of the condyle: divided into trochlea and capitulum. 5.^ Trochlea (I, III, IV): the medial part of the articular surface crossed by A. Head (II, IV): the rounded process directed caudally to a groove for the trochlear notch of the ulna articulate with the smaller glenoid cavity of the scapula, 6. ^Capitulum (I, III, IV): the lateral part of the condyle that articulates thus, forming the shoulder joint. with the head of the radius (I): the opening between the olecranon and radial B. Greater tubercle (I, II, IV): the palpable, large process cran- 7. Supratrochlear foramen fossa in the dog. It may not be present as nothing passes through it. iolateral to the humeral head for muscle attachments. - C. Point of the shoulder (I, II): the palpable surface feature of the forearm. It is known as the extensor epicondyle. formed by the cranial part of the greater tubercle. - H. Medial (flexor) epicondyle (I, II, IV): the large, caudally D. Lesser tubercle (I, II, IV): the process medial to the directed projection that prevents medial luxation of the humeral head. elbow. It is functionally known as the flexor epicondyle E. Intertubercular (bicipital) groove (I, II): the sulcus be- as it is the attachment for the forearm flexor muscles. tween the greater and lesser tubercles through which the - I. Olecranon fossa (IV): the caudal excavation on the distal tendon of the biceps brachii m. runs. humerus receiving the anconeal process of the ulna on F. Deltoid tuberosity (I): the small process on the lateral side extension of the elbow. of the humerus for the insertion of the deltoideus m. CLINICAL: G-I. Humeral condyle: the entire cylindrical, distal extrem- • Humeral fractures: majority in the middle and ity of the humerus (there is only 1). distal third where there is a chance of radial n. - G. Lateral (extensor) epicondyle (I, III, IV): the lateral damage. Treat with open reduction and internal side of the humeral condyle giving rise to the extensors fixation. 34 II Thoracic Limb RADIUS & ULNA E E. Point of the elbow, 3* G. Anconeal process 3* G G D F. Trochlear notch D F 1* F D. Olecranon 1* * H 4 4* H. Med. coronoid process C C. ULNA A A A. RADIUS J. Interosseous space II. Left ulna and radius, cranial view 7* B. Styloid process (radius) I III. Right ulna: cranial view I. Styloid process and radius, caudal view I. Left ulna and radius, lateral view I FOREARM ANTEBRACHIUM B or : formed by the ulna and 1.