Some Efferent Neocortical Pro Jections in the Armadillo Dasypus Novemcinctus

This dissertation has been microfilmed exactly as received 69-22,141

HARTING, John Kelly, 1942- SOME EFFERENT NEOCORTICAL PRO JECTIONS IN THE ARMADILLO DASYPUS NOVEMCINCTUS.

The Ohio State University, Ph.D., 1969 Anatomy

University Microfilms, Inc., Ann Arbor, Michigan SOME EFFERENT NEOCORTICAL PROJECTIONS IN THE

ARMADILLO DASYPUS NOVEMCINCTUS

DISSERTATION

Presented In Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of Hie Ohio State University

John Kelly Harting, B.A., M.Sc

********

5he Ohio State University 1969

Approved by

Department of Anatomy ACKNOWLEDGMEHTS

The author wishes to express his most sincere appreciation to his adviser, Dr. George F. Martin, whose constant availability and willingness to give assistance whenever needed will always be remem bered. He has set an example for his graduate students to follow— an example that I would some day like to project to my students. Hie author also would like to acknowledge Miss Marjorie Stuber for tech

nical assistance, Mr. Gabriel Falkuti for preparation of photographic material, Mrs. Barbara Jordon for typing of the first manuscript, and

Drs. Ronald L. St. Pierre and James S. King for reading of the manuscripts.

Finally, I would like to thank my mother for her continued

"support" throughout ray academic career. Her confidence in me was

certainly most instrumental in the attainment of this degree.

ii VITA

January 1, 19^2 Bora - Cincinnati, Ohio

1961* ...... B.A., Ohio Wesleyan University, Delaware, Ohio

196l*-66 . . . . Graduate Assistant, Department of Anatomy, The Ohio State University, Columbus, Ohio

1966 M.Sc., The Ohio State University, Columbus, Ohio

1 9 6 6 -6 9 Teaching Associate, Department of Anatomy, The Ohio State University, Columbus, Ohio

PUBLICATIONS

Fisher, A. M., J. K. Harting, G. F. Martin, and M. I. Stuber 1969 The origin, course and termination of the corticospinal fibers in the armadillo. J. Neurol. Sci., 8:3^7-3 6 1.

Harting, J. K. 1969 Corticomesencephalic projections in the arma dillo. Anat. Rec., 1 6 3:1 96-1 9 7.

FIELDS OF STUDY

Major Field: Anatomy

Studies in Neuroanatomy. Assistant Professor George F. Martin Studies in Histology. Professor John A. Eglitis Studies in Embryology. Associate Professor John Weston Studies in Gross Anatomy. Professor Irma Eglitis

lii TABLE OF CONSENTS

Page ACKNOWLEDGMENTS...... ii

VITA ...... Ill

LIST OF ILLUSTRATIONS...... v

PART I. NEOCORTICAL PROJECTIONS TO THE MESENCEPHALON IN SHE NINE-BANDED ARMADILLO (DASYPUS NOVEMCINCTUS)

INTRODUCTION...... 2

MATERIALS AND ME SHOPS...... If

RESULTS ...... 5

DISCUSSION...... 14

SUMMARY...... 22

LITERATURE C I T E D ...... 44-

PART II. NEOCORTICAL PROJECTIONS TO THE PONS AND MEDULLA IN THE NINE-BANDED ARMADILLO (DASYPUS NOVEMCINCTUS)

INTRODUCTION...... 48

MATERIALS AND METHODS...... 50

RESULTS...... 51

DISCUSSION...... 58

SUMMARY...... 68

LITERATURE C I T E D ...... 80

It LIST OF ILLUSTRATIONS

Figure Page

1. Gross brain of the armadillo...... 2k

2. Coronal sections illustrating the corticomesencephalic projections arising from the most rostral tip of the n e o c ortex...... 2 6

3* Coronal sections illustrating the corticomesencephalic projections arising from the mid-presupraorbital neo co r t e x ...... 28

4. Coronal sections illustrating the corticomesencephalic projections arising from the neocortex immediately rostral to the supraorbital buIcub...... 30

3. Photographs illustrating degeneration resulting from a lesion of the mid-presupraorbital n e o c ortex...... 32

6. Coronal sections illustrating the corticomesencephalic projections arising from the neocortex immediately caudal to the supraorbital s u l c u s ...... 3*t

7. Photographs illustrating degeneration resulting from a lesion of the neocortex immediately caudal to the supraorbital sulcus ...... 36

8. Coronal sections illustrating the corticomesencephalic projections arising from the caudal one-third of the neocortex ...... 3@

9. Coronal sections illustrating the corticomesencephalic projections arising from the most caudal tip of the n e o c o r t e x ...... ^0

10. Photographs illustrating degeneration resulting from a lesion of the caudal one-third and most caudal pole of the neocortex...... k2

11. Coronal sections illustrating the neocortical projec tions to the ponB arising from the most rostral pole of the neocortex (left) and from the mid-presupra orbital neocortex (right) ..... 70

v LIST OF ILLUSTRATIONS--Continued

Figure Page

12. Coronal sections Illustrating the neocortical projec tions to the pons and medulla arising from the neocortex Immediately caudal to the supraorbital sulcus...... 72

13. Coronal sections illustrating the neocortical projec tions to the pons ariBlng from the caudal one-third (left) and most caudal pole (right) of the neocortex . . 7^

1^. Photographs illustrating degeneration vithin the basilar pontine gray resulting from lesions of the more rostral and caudal neocortex...... 76

15. Photographs illustrating degeneration vithin the pons and medulla resulting from lesions of the neocortex immediately caudal to the supraorbital sulcus ...... 78

vi PART I

NEOCORTICAL PROJECTIONS TO THE MESENCEPHALON IN THE

NINE-BANDED ARMADILLO DASYPUS NOVEMCINCTUS

1 INTRODUCTION

The mesencephalon Is undoubtedly an Important brainstem region for the regulation of motor activity (Denny-Brown, 1 9 6). 2 This brain stem region has been suggested as being particularly important In forms such as the opossum (Martin, 1 9 6), 8 which possesses a limited cortico spinal tract. Previns studies concerning neocortical projections to the midbrain have been generally limited to the opossum (Martin, 1 9 6), 8 the cat (Altman, 1962; Rinvik and Walberg, 1 9 6; 3 Sprague, 1963; Rinvik,

1 9 6 6), and certain primates (Levin, 1936; Whitlock and Kauta, 1956;

Meyers, 1963; DeVito and Smith, 196^; Kuypers and Lawrence, 1 9 6 7). Bie present Investigation was undertaken to determine the pattern and certain details of neocortical projections to the mesencephalon in the nine-banded armadillo, a representative of the order Edentata. It is hoped that by extensive sampling of the various lines of living eutherian mammals a basic pattern of such connections will become apparent and, Just as importantly, that any differences in the specifics of these pathways may be ascertained.

Ihe gross brain of the armadillo (Fig. l) was first described by G. Elliot Smith (1 8 9)* 9 Further anatomical Investigations were undertaken by Fapez (1932) and Crosby and Woodbum (19^3)• Crosby and

Woodburo described the nuclear pattern of the non-tectal portions of the midbrain and isthmus and their descriptions, together with Fapez*s

2 3 atlas of the diencephalon and rostral mesencephalon, vere utilized,

In the present study, to identify the nuclear groups to which degenerating fibers were traced. MATERIALS AND METHODS

Neocortical lesions vere placed in a rostral to caudal sequence in a total of 12 armadillos. While the majority of ablations involved the cortex in close proximity to the supraorbital sulcus (Figs. U and

6), two smaller lesions vere placed in the most rostral (Fig. 2) and caudal (Fig. 9) poles of the neocortex. One lesion involved the caudal one-third of the neocortex (Fig. 8), but did not extend as far caudally as the smaller lesion of the caudal pole.

The animals vere alloved to survive for a period of 7-1^ days.

They vere then sacrificed by perfusion vith 0.9^ saline folloved by buffered formalin, and the brains and spinal cords removed. Serial sections vere then cut on a freezing microtome and subsequently subjected to the Nauta-Gygax technique (Nauta and Gygax, 195*0 for demonstration of degenerating axons. The limits of each lesion vere defined histologically and any damaged vhite matter vas noted. Thionin

stained preparations of the armadillo brain vere employed to help

elucidate the cytoarchitecture of the mesencephalon. RESULTS

Hie results obtained from this study will be described under the following subdivisions: (a) those from a brain subjected to a lesion of the most rostral neocortex; (b) those from a brain subjected to a lesion of the mid-presupraorbital neocortex; (c) ttaOBe from brains with lesions immediately rostral to the supraorbital sulcus; (d) those from brains with ablations immediately caudal to the supraorbital sulcus; (e) those from a brain with a lesion within the caudal one- third of the neocortex; and (f) those from a brain with a lesion of the most caudal neocortex. All cortical regions lesioned will be described in relation to the supfaorbital sulcus or in relation to the rostral or caudal poles of the neocortex since neither cytoarchitectonic nor physiological studies of the armadillo neocortex are available.

In the case of each particular cortical lesion, the predominant projections to the thalamus will be briefly described in order to establish certain patterns rostral to the mesencephalon.

Lesion of the most rostral tip of the neocortex

Degenerating fibers resulting from a small lesion of the most rostral pole of the neocortex (Pig. 2) coursed caudally and ventrally through the subcortical white matter and into the ventral portion of the anterior limb of the Internal capsule. Hie majority of Injured fasicles continued caudally and eventually assumed a position within

5 6 the most medial portion of the ipsilateral cerebral peduncle. A con siderable number of degenerating fibers left the Internal capsule and cerebral peduncle and entered the inferior thalamic radiations. Such fibers terminated vithin the central nucleus, the paracentral nucleus, the ventral median nucleus, and the lateral part of the dorsal median nucleus of the thalamus.

At rostral mesencephalic levels degenerating fibers terminated vithin the ventral periaqueductal gray, the nucleuB of the commissure of Forel and vithin the medial substantia nigra (Fig. 2). More caudally the predominant areas of termination vere located vithin the ventral and medial areas of the mesencephalic tegmentum. More specifically, degenerating fascicles terminated vithin the ventral periaqueductal gray, the rostral linear nuclei, the ventral tegmental area of Tsai, and the medial substantia nigra (Fig. 2). Fev, if any, degenerating fibers terminated vithin either the parvocellular or magnocellular divisions of the red nucleus. Although there is no detailed cyto architectural evidence available vhich verifies the presence of magnocellular and parvocellular divisions of the armadillo red nucleus, Crosby and Woodburn (19^3) utilized these terms in their descriptions of the nuclear pattern of the nontectal portion of the armadillo mesencephalon. Therefore the terms vill be used in this study. At rostral pontine levels degenerating fibers ended vithin the medial and ventral areas of the baBilar pontine gray (Fig. 2). Lesion of the mid-presupraorbital neocortex

Degenerating fibers resulting from a lesion of the mid- presupraorbital neocortex (Fig* 3) coursed caudally through the subcortical uhite matter and passed into the ventral portion of the anterior limb of the internal capsule. Such fibers vere generally located dorsal to those described from the rostral tip of the neocortex.

The majority of degenerating fibers assumed a position vithin the ventral-medial portion of the ipsilateral cerebral peduncle, but some vere located more laterally in the peduncle than vas the case in the brain vith the lesion limited to the rostral tip of the neocortex. At rostral thalamic levels, injured fascicles entered the inferior thalamic radiations and terminated vithin the central nucleus, the median nucleus, the ventral median nucleus, and throughout the dorsal median nucleus of the thalamus (Fig. 3)* A small number of degenerating fibers passed through the central nucleus of the thalamus and terminated on the side contralateral to the lesion.

The majority of degenerating fibers emanating from the cerebral peduncle at mesencephalic levels coursed ventrally and medially and terminated vithin the ventral periaqueductal gray, the rostral linear nuclei (Figs. 3 and and the ventral tegmental area of Tsai (Figs. 3 and ^d)• Degenerating axons ended throughout the rostral 11mltB of the red nucleus, but at more caudal levels the amount of terminal degener ation vas significantly decreased and limited, for the most part, to the dorsal-lateral and ventral-medial areas of the nucleus. Ho degen erating fibers vere Judged to terminate vithin the most caudal tip of the red nucleus. Still other degenerating fibers passed dorsally and laterally to terminate vithin the nucleus mesencephallcus profundus dorsalis (Fig. 3)* A considerable number of these fascicles continued dorsally and ended profusely vithin the ventral nucleus of the periaqueductal gray (Figs. 3 and 5»)* At rostral pontine levels, degenerating fibers terminated vithin the dorsal, the medial, and the ventral areas of the basilar pontine gray (Fig. 3)*

Lesions of the neocortex immediately rostral to the supraorbital sulcus

Degenerating fibers resulting from an ablation of the neocortex immediately rostral to the supraorbital cortex (Fig. 4) coursed caudally through the subcortical vhite matter and passed into the ventral por tions of the anterior limb of the internal capsule. The majority of injured fiber bundles eventually coursed vithin the ventral and medial aspect of the ipsilateral cerebral peduncle. At rostral thalamic levels degenerating fibers ended vithin the central nucleus, the median nucleus, the dorsal median nucleus, the lateral portions of the ventral median nucleus, and vithin the medial portion of the ventral lateral nucleus

(Fig. 4). Further caudally, injured fibers entered the Intermediate thalamic radiations and terminated vithin the lateral portion of the ventral median nucleus, the medial aspect of the ventral nucleus and vithin the parafascicular and posterior nucleus of the thalamus (Fig. *0.

At mesencephalic levels degenerating fibers terminated vithin the rostral linear nuclei, the ventral tegmental area, the medial and Intermediate substantia nigra, the mesencephalic reticular formation and vithin the red nucleus (Fig* 4). However, in contrast to the lesion of the mid-presupraorbital cortex, degenerating fibers also terminated vithin the dorsal lateral tegmentum (Fig. 4). In the armadillo, the dorsal lateral tegmentum Includes the lateral nucleus of the thalamus (pars posterior), the pretectal area, and the caudal pretectal nucleus. At rostral pontine levels degenerating fibers distributed to the dorsal medial, the medial, the ventral and the lateral areas of the basilar pontine gray (Fig. 4-).

Lesions of the neocortex immediately caudal to the supraorbital sulcus

In this relatively lissencephalic brain it was difficult to obtain ablations caudal to the supraorbital sulcus vhlch did not infringe upon underlying white matter. However, the results obtained from all such lesions vere decidedly different from those obtained from lesions rostral to the sulcus. In this way the results from more rostral cortical ablations served as partial controls for interpreting the findings from brains with lesions immediately caudal to the supraorbital sulcus.

Degenerating fibers resulting from lesions of the neocortex immediately caudal to the supraorbital sulcus (Fig. 6) coursed through the subcortical white matter and into the anterior limb and genu of the internal capsule. These fibers assumed an intermediate position vithin the cerebral peduncle. At thalamic levels, degenerating fascicles entered the ventral and intermediate thalamic radiations and terminated extensively throughout the ventral lateral nucleus of the thalamus

(Fig. 6). Scattered degenerating fascicles coursed vithin the inferior 10 thalamic radiations and passed through the ventral median nucleus of the thalamus to reach the side contralateral to the lesion (Fig. 6).

A small number of injured fibers entered the dorsal thalamic radiations and terminated vithin the pretectal area and the pretectal nucleus.

At mesencephalic levels, degenerating fibers terminated vithin the lateral periaqueductal gray, the Intermediate substantia nigra

(Fig. 6), and vithin the nucleus mesencephallcus profundus dorsalis

(Figs. 6 and 7c). Degenerating fibers ended throughout the rostral and intermediate regions of the red nucleus and vere not restricted to limited portions of those areas of the nucleus (Figs. 6 and 7b)* Fev, if any, degenerating fibers terminated vithin the caudal tip of the red nucleus. The majority of degenerating fibers coursed dorsally and laterally, passing uninterrupted through the mesencephalic reticular formation, and terminated profusely vithin the dorsal lateral tegmentum

(Figs. 6 and 7a) and vithin the deeper layers of the lateral one-half of the rostral superior collicuius (Fig. 6).

Lesion of the caudal one-third of the neocortex

Degenerating fibers resulting from a large lesion vithin the

caudal one-third of the neocortex coursed through the subcortical vhite

matter and Into the caudal extent of the internal capsule. At rostral

thalamic levels, degenerating fascicles vere positioned vithin the

lateral one-half of the cerebral peduncle and terminated vithin the

ventral and dorsal nuclei of the lateral geniculate body (mainly vithin

the ventral nucleus), the lateral nucleus of the thalamus, and vithin 11 the pretectal area. Also as this level, scattered fibers distributed to the lateral one-half of the rostral superior collicuius (Fig. 8).

At rostral mesencephalic levels, fibers coursed dorsally laterally from the cerebral peduncle and terminated within the deeper layers of the superior colllculus, especially within its lateral one- half (Fig. 8). Some fibers in this bundle passed laterally and ended within the central nucleus of the medial geniculate body (Fig. 8).

Other fibers of the same bundle passed medially and terminated within the mesencephalic reticular formation and within the lateral periaque ductal gray (Fig. 8). Degenerating fibers also terminated throughout the rostral and intermediate portions of the red nucleus and, although the number of degenerating fibers progressively decreased from rostral to caudal, most of the red nucleus contained scattered degenerating fibers. However, degenerating fibers were not observed in the most caudal tip of the nucleus.

At the junction of the superior and inferior colllculus, degenerating fibers terminated within the cuneiform nucleus, the adjacent lateral periaqueductal gray, and within all layers of the caudal superior colllculus (Figs. 8 and 10a). A few fibers left the cerebral peduncle and entered the bracbium of the inferior colllculus.

Such fibers terminated predominantly within the medial area of the nucleus of the inferior colllculus. At rostral pontine levels, degen erating fibers ended within the lateral and ventral areas of the basilar pontine gray (Fig. 8). 12

One large neocortical ablation vas accomplished In the most ventral and caudal portions of the neocortex, Just dorsal to the rhinal fissure(Fig. l). Although technical problems vere encountered and consequently the results of this lesion are not described in detail, degenerating fibers vere observed vithin the central nucleus of the medial geniculate body.

Lesion of the most caudal pole of the neocortex

In one ArHtha! the neocortical ablation vas limited to the most caudal pole of the neocortex (Fig. 9)* Degenerating fibers resulting from that lesion coursed through the subcortical vhite matter and into the caudal extent of the internal capsule. At thalamic levels, these fibers vere positioned vithin the most dorsal and lateral extreme of the ipsilateral cerebral peduncle (Fig. 9)* Fibers passed dorsally from the cerebral peduncle and terminated vithin the ventral and dorsal nuclei of the lateral geniculate body (Fig. 9)* As vas the case in the larger lesion previously described (Fig. 8), most of these fibers ended vithin the ventral nucleus. Degenerating fascicles entered the bra chi uni of the superior colllculus and ended vithin the superficial layers of the lateral one-half of the rostral superior colllculus

(Fig. 9). More caudally, degenerating fascicles passed from the brachium of the superior colllculus and entered the stratum opticum of the superior colllculus (Figs. 9 and 10b), Some of these fibers terminated vithin stratum optician, vhereas the remaining fibers ended in the stratum griseum intermedia and stratum grlseum superficialls. A

small number of the degenerating fibers that had entered the brachium of the superior colllculus at rostral levels terminated vithin stratum zonale and coursed ventrally to end vithin stratum opticum, the stratum griseum superficialis and the stratum griseum intermedia. Although the predominant area of termination vas in the lateral one-half of the superior colllculus, scattered degenerating fiberB terminated vithin similar layers in the medial aspects of the superior colllculus. DISCUSSION

It is evident from the foregoing observations that there is a pattern of neocortical projections to the mesencephalon in the arma dillo. In the following discussion, corticomesencephalic projections will be discussed under the following four divisions: (a) projections of the neocortex rostral to the supraorbital sulcus; (b) projections of the neocortex immediately caudal to the supraorbital sulcus; (c) pro jections of the caudal one-third of the neocortex; (d) projections of the moBt caudal pole of the neocortex* The neocortical projections to the thalamus were described for completeness, but will not be discussed in this section.

Projections of neocortex rostral to the supraorbital sulcus

The results of the present study suggest that, for the most part, the neocortex rostral to the supraorbital sulcus projects to the ventral and medial areaB of the mesencephalon. However, the results also indicate that this rostral neocortical area is not completely uniform in its efferent connections. Degenerating fibers resulting from the most rostral lesion (Fig. 2) terminated within the ventral periaqueductal gray, the rostral linear nuclei, the ventral tegmental area and within the medial substantia nigra (Fig. 2). Degenerating fascicles from the mid-presupraorbital ablation distributed to the same ventral and medial areas as the smaller, more rostral lesion, but in addition, degenerating fascicles terminated vithin the ventral nucleus lM of the periaqueductal gray, vithin the magnocellular and parvocellular portions of the red nucleus, and vithin portions of the mesencephalic tegmentum dorsal and lateral to the red nucleus (Fig. 3)• The results of an ablation immediately rostral to the supraorbital sulcus vere similar to those obtained from the leBlon of the mid-presupraorbital neocortex, but in addition, degenerating fibers terminated vithin the dorsal lateral tegmentum of the mesencephalon (Fig. k).

Hie results of an earlier Btudy (Fisher et al., 1 9 6 9) Indicate that in the armadillo corticospinal fibers arise from cortices imme diately rostral and caudal to the supraorbital sulcus. Corticospinal fibers arising from the neocortex immediately rostral to the supra orbital sulcus terminated vithin the ventral and lateral areas of the spinal cord gray as far caudally as More specifically, degener ating fibers terminated vithin the ventral and lateral portions of lflHinA V, vithin 1 nn. VX, and vithin the dorsal and lateral area of lamina VII. Also, some degenerating fibers terminated vithin lamina VIII. By combining these results vith those obtained in the present study, it can be seen that the neocortex immediately rostral to the supraorbital sulcus projects to both the ventral and lateral portions of the spinal cord gray matter and to the magnocellular division of the red nucleus. Such results partially agree vith observations made in the cat (Hyberg-Hansen and Brodal, 19*53; Rinvik: and Walberg, 1 9 6 3), and the monkey (Lui and Chambers, 1 9 6 k; Kuypers and

Lawrence, 1 9 6)* 7 which Indicate that cortices rostral to the cruciate 16 and. central sulci respectively project not only to more ventral lateral areas of the spinal cord gray, hut also to the magnocellular red nucleus. The present authors do not intend to imply that the presupraorbital neocortex of the armadillo is homologous vith the pre- cruciate cortex of the cat or the precentral cortex of the rhesus monkey, but only that they are similar in terms of certain efferent projections. This pattern of projection to the spinal cord gray and to the red nucleus differs from that described in the opossum, in vhlch the neocortex rostral to the orbital sulcus contributes few, if any, corticospinal fibers (Martin and Fisher, 1968) and only scattered fibers to the magnocellular division of the red nucleus (Martin, 1968;

Martin and Fisher, 1 9 6 8).

As vas mentioned previously, the corticospinal fibers in the armadillo extend only to mid-thoracic levels (Fisher et al., 1 9 6 9)*

However, degenerating fibers vithin the magnocellular division of the red nucleus resulted from ablations of both the mid-presupraorbital neocortex and the neocortex immediately rostral (and caudal) to the supraorbital sulcus. If rubrospinal fibers traverse the entire spinal cord in the armadillo aB they do in the opossum (Martin et al., 1 9 6 8), the cat (Nyberg-Hansen and Brodal, 1 9 6 k), and the monkey (Poirier and

Bouvier, 1 9 6), 6 this broad area of corticorubral origin may give the neocortex indirect control over lover motor neuron activity within lumbosacral cord.

Degenerating fibers, resulting from ablations of the mid- presupraorbital. cortex (Fig. 3) and the cortex immediately rostral to the supraorbital sulcus (Fig. 4) were extensive within the ventral 17 nucleus of the periaqueductal gray. The significance of this mesen cephalic area has not been established for any fora. The proximity of this nuclear region to the oculomotor and trochlear nuclei suggests that it may be connected vith neurons Innervating extrinsic muscles of the eye. Since cortical fibers vere not found to terminate vithin either the oculomotor or trochlear nuclei, neocortical initiation of eye movements in the armadillo may Involve internuncial neurons vithin the ventral nucleus of the periaqueductal gray. It has also been sug gested in the opossum (Martin, 1968) that the ventral nucleus of the periaqueductal gray may be concerned vith visceral function due to its close relationship to the sulcus limitans and to the dorsal longi tudinal fasciculus.

Projections of neocortex immediately caudal to the supraorbital sulcus

The results of the present study indicate that cortical areas immediately caudal to the supraorbital sulcus of the armadillo project to somevhat different regions of the mesencephalon than do cortices rostral to that same sulcus. Degenerating fibers resulting from lesions immediately caudal to the supraorbital sulcus assumed an inter mediate position vithin the cerebral peduncle and terminated vithin the lateral periaqueductal gray, the Intermediate substantia nigra, the parvocellular and magnocellular red nucleus, the mesencephalic reticular formation, the deeper layers of the lateral one-half of the superior colllculus, and extensively vithin the dorsal lateral midbrain tegmentum

(Fis. 6). This neocortical area also projects to certain brain stem sensory nuclei (Harting and Martin, 19&9* 1° Preparation) and contributed 18 corticospinal fibers vhich terminate in the more medial portions of the base of the dorsal horn (Fisher et al., 1969). In the monkey, the areas of cortex vhich project to the dorsolateral midbrain tegmentum, to brainstem Bensory nuclei and to more dorsal and medial areas of the spinal cord gray are limited primarily to the granular postcentral and parietal regions (Kuypers and Lawrence, 1 9 6 7). lhe post-supraorbital cortex of the armadillo appears to be generally comparable to cortical areas caudal to the central sulcus of the monkey, at least in the terms of its efferent projections. Again, it should be emphasized that such a comparison must be made vith reservations, since cytoarchitectonic studies of the armadillo neocortex are not completed, and as yet, there are not stimulation or evoked potential studies available for the armadillo.

A somatotopic organization of cortical projections to the red nucleus has been described in the cat (Rinvik and Walberg, 1 9 6; 3

Mabuchl and Kasama, 1 9 6 6) and monkey (Kuypers and Lawrence, 1 9 6). 7 In both forms, the forelimb cortical centers project to somewhat different portions of the red nucleus than do the hindlimb regions. No apparent organization of corticorubral projections was evident In the armadillo material studied thus far, but subsequent placement of smaller lesions in a dorsal-lateral to ventral-medial sequence, both rostral and caudal to the supraorbital sulcus, may shed further light on this problem.

However, since the armadillo possesses direct neocortical control over

internuncial neuronB vithin the cervical spinal cord, but not the

lumbosacral cord, a somatotopic pattern of corticorubral projections 19 similar to that possessed by the cat and monkey, vhich possess cortico spinal fibers traversing the entire spinal cord, might not be expected.

It was previously stated that there vere no direct projections from presupraorbltal cortex to cranial nerve motor nuclei located in the mesencephalon, nils is also true of the neocortex caudal to the supraorbital sulcus. However, it Is possible that a significant number of the projections from the cortex Immediately caudal to the BUpra- orbital sulcus are motor In nature due to the large number of fibers terminating within the nucleus mesencephalicus profundus dorsalis (deep mesencephalic reticular formation) and within the red nucleus (Fig. 6).

It is also probable that some of the post-supraorbital projections to the dorsolateral midbrain tegmentum play an important role in the modulation of ascending sensory pathways which have been reported to give collaterals to that region in the monkey (Kuypers and Lawrence,

1 9 6 7) and in man (lfauta and Kuypers, 1 9 5 8).

Projections of the caudal one-third of the neocortex

In another, more caudally placed lesion behind the supraorbital sulcus (Fig. 8), considerable white matter t'as undercut. Degenerating fibers resulting from this lesion terminated within both the large and small cell portions of the red nucleus, the dorsolateral midbrain tegmentum, all layers of the superior collicuius, the nucleus centralis of the medial geniculate body and within the nucleus of tho inferior colliculus (Fig. 8). Die corticorubral projections suggest that either the area of cortex giving rise to such pathways extends as far caudally as the location of the lesion, or that projection fibers of cortex rostral to the lesion were undercut. 20

Projections from temporal cortex in the opossum (Martin, 1 9 6 8) and cat (Whitlock and Nauta, 1956) have been described as terminating vithln the central nucleus of the medial geniculate body, the ipsilat-

eral nucleus of the Inferior collicuius, and vithin the deeper layers

of the superior colliculus. Also in the monkey, projections from

temporal neocortex terminate in the central nucleus of the medial

geniculate body (Whitlock and Bauta, 1956) within the superior collicu

lus (Thompson, 1900; Kuypers and Lawrence, 1 9 6 7) and vithin the nucleus

of the inferior colliculus (Thompson, 1900; Kuypers and Lawrence, 1 9 6). 7

Since, in the armadillo brain described above, degenerating fibers

resulting from the lesion of the caudal one-third of the neocortex ended

within the central nucleus of the medial geniculate body, the ipsilat-

eral nucleus of the inferior colliculus and within the deeper layers of

the superior colliculus, it seems possible that white matter emanating

from regions comparable to "temporal" cortex was undercut. The results

obtained from a single ventral, caudal lesion dorsal to the rhinal fis

sure ("temporal area"), also suggests that this was the case. Neocortl-

cal pathways to the nucleus of the inferior colliculus, as well as to

the medial geniculate nucleus, suggest that a portion of the armadillo

cortex, probably "temporal cortex," may subserve a regulatory function

on relay nuclei within the auditory system. Degenerating fibers

resulting from the lesion of the caudal one-third of the neocortex were

also observed to terminate vithin the lateral geniculate nuclei and the

superficial layers of the superior colliculus. Such results would

indicate that part of the lesloned cortex is either comparable in its 21 efferent projections to a perlstriate area, and/or that fibers from the caudal pole of the neocortex were undercut.

Projections of the most caudal pole of the neocortex

The lesion of the moBt caudal tip of the neocortex projected to only the superficial layers of the superior colliculus. This includes the stratum zonale, the stratum griseum superficialls, the stratum opticum and the stratum griseum intermedia. These layers are known to receive fibers from the optic tract in various mammals (Crosby and

Henderson, 1948) and also to receive input from the caudal neocortex in the opossum (ifartin, 1 9 6), 8 the rat (Nauta and Bucher, 1954; Lund,

1966), the cat (Sprague, 1 9 6 3), and the monkey (Kuypers and Lawrence,

1967)» Neocortical pathways to such layers of the superior colliculus, along with those to the pretectum, possibly enable the caudal neocortex to assist in the modulation of incoming visual information at the level of the superior colliculus. Although evoked potential studies are not available on the armadillo, it may be predicted that on the basis of its efferent connections, the most caudal neocortex will prove to be the primary visual area. SUMMARY

Die results of this study Indicate a definite pattern of neocortical projections to the mesencephalon in the nine-banded armadillo. This pattern closely parallels that described for certain other eutherlan mammals, but differs in certain specifics.

Degenerating fibers resulting from a lesion of the mid- presupraorbital neocortex assumed a position vithin the most medial aspect of the cerebral peduncle and projected to the ventral and medial areas of the mesencephalon. Such areas included the ventral nucleus of the periaqueductal gray, the rostral linear nuclei, the ventral tegmental area, the medial substantia nigra, and the magnocellular and parvocellular divisions of the red nucleus. The rostral tip of the neocortex, vhile projecting to similar mesencephalic areas as the mid- supraorbital neocortex, did not distribute degenerating fascicleB to either the red nucleus or the ventral nucleus of the periaqueductal gray. The projection pattern of the neocortex immediately rostral to the supraorbital sulcus vas also similar to that of the mid-supraorbital cortex, but in addition degenerating fibers terminated vithin the dorsal lateral tegmentum.

Degenerating fibers emanating from lesions immediately caudal to the supraorbital sulcus vere positioned vithin the intermediate areas of the ipsilateral cerebral peduncle and terminated extensively vithin

22 the dorsal lateral tegmentum of the midbrain, the mesencephalic reticular formation, the intermediate substantia nigra, and within the parvocellular and magnocellular divisions of the red nucleus. Injured fascicles resulting from a lesion of the caudal one-third of the neo cortex were located in the more lateral aspects of the cerebral peduncle and projected to more dorsal portions of the mesencephalon, as well as to certain mesencephalic areas which received cortical input from the cortex immediately caudal to the supraorbital sulcus. A small neocortical ablation of the most caudal pole of the neocortex con tributed degenerating fascicles that assumed a position within the most dorsal and lateral portion of the cerebral peduncle and terminated mainly within the superficial layers of the superior colliculus. 211-

FIG. 1. Photograph of the gross brain of the nine-banded armadillo.

SO - supraorbital sulcus

RF = rhinal fissure

FfR t= pyriform cortex

OB ■* olfactory bulb

PIG. 2. A series of coronal sections through the caudal thalamus, the mesencephalon and roBtral pons of an armadillo subjected to a lesion of the most rostral tip of the neocortex. Degenerating fibers of passage are indicated by broken lines vhereas terminal degeneration is shovn by dots.

CP m cerebral peduncle FI ■ fornix HIT ■ habenulo-interpeduncular tract IC a Inferior colliculus INCF *» interstitial nucleus of the commissure of Forel MLF a medial longitudinal fasciculus IP ■ interpeduncular nucleus Iv a trochlear nucleus IBS « lesion RL > rostral linear nuclei HN a red nucleus SN « substantia nigra TV a ventral tegmental nucleus of Tsai

FIG. 3* A series of coronal sections through the thalamus, the mesencephalon, and the rostral pons of an armadillo subjected to a lesion of the mid- presupraorbital neocortex. Degenerating fibers of passage and their terminations are indicated as in Fig. 2.

CEH x central nucleus CP - cerebral peduncle DM » dorsal median nucleus H « fornix GCPV * ventral nucleus of the periaqueductal gray HIT x habenulo-Interpeduncular tract INCF x interstitial nucleus of the commissure of Forel Iv m trochlear nucleus LES x lesion MED x median nucleus MLF x medial longitudinal fasciculus MFD x nucleus mesencephalicus profundus dorsalis (deep reticular formation) FCN x paracentral nucleus BL x rOBtral linear nuclei KN x red nucleus SN x substantia nigra TV x ventral tegmental nucleus of Tsai VM x ventral medial nucleus LES hit- ^ MEt^n-^PCN :v"A 'v 3.:-^ v . ' o.A V\'

o Cl? 30

FIG. A series of coronal sections through thalamus, the mesencephalon and the rostral pons of an armadillo subjected to a lesion of the neocortex Immediately rostral to the supraorbital sulcus. Degenerating fibers of passage and their terminations are indi cated as in Fig. 2.

CEN ** central nucleus CP « cerebral peduncle FX * fornix GCPV - ventral nucleus of the periaqueductal gray HIT » habenulo-lnterpeduncular tract IP » interpeduncular nucleus LES - lesion MED « median nucleus PARF ■ parafascicular nucleus PCN ■ paracentral nucleus PP “ posterior periventricular gray PRETECT » pretectal nucleus RL - rostral linear nuclei RN m red nucleus SN * substantia nigra TV - ventral tegmental nucleus of Tsai VL « ventral lateral nucleus VM - ventral median nucleus

FIG. 5 . Photomicrographs illustrating preterminal and terminal degeneration vlthin the ventral nucleus of the peri aqueductal gray (a), rostral linear nucleus (b), the medial substantia nigra (c), and the ventral tegmental area (d) resulting from a lesion of the mid-preaupra- orbital neocortex.

Kauta-Gygax technique l»jC wsq & fc £

f f l

m ■Jk* -r-v 3^

FIG. 6. A aeries of coronal sections through the caudal thalamus, the mesencephalon and the rostral pons of an armadillo subjected to a lesion of the neocortex immediately caudal to the supraorbital sulcus. Degenerating fibers of passage and their endings are indicated as in Fig. 2.

CP ■ cerebral peduncle CU ■ cunieform nucleus FX » fornix HIT » faabenulo-lnterpeduncular tract IC ■ Inferior collieulus IP ** interpeduncular nucleus iv ■ trochlear nucleus _ LES =» lesion MLF a medial longitudinal fasciculus MFD a nucleus mesencephalicus profundus dorsalis (deep reticular formation) PARF « parafascicular nucleus PP a posterior periventricular nucleus PHETECT a pretectal nucleus POST a posterior nucleus of the thalamus KH * red nucleus SN a substantia nigra VL a ventral lateral nucleus POST

PARF-

TV its*/**! I1 36

FIG. 7* Photomicrographs illustrating preterminal and terminal degeneration vithin the dorsal lateral tegmentum (a), the aagnocellular red nucleus (b), and vithin the nucleus mesencephalon profundus dorsalis (c) resulting from lesions immediately caudal to the supraorbital sulcus. (Fig. 6).

Nauta-Gygax technique 37

* ** > . -m. -m P

'iti

WPj5*R*i k^r * ’-' 3ss?»

■ * v ^ ;

'- • *v 1 I 'Ki & - > . '

§ 38

FIG* 8. A series of coronal sections through the caudal thalamus, the mesencephalon and the rostral pons of an armadillo subjected to a lesion of the caudal, one-third of the neocortex* Degenerating fibers of passage and their endings are indicated as in Fig. 2.

CP * cerebral peduncle CU ■» cunieform nucleus FX - fornix GMC - nucleus centralis of the medial geniculate body HIT =* habenulo-interpeduncular tract IC — inferior collicuius IP ■ interpeduncular nucleus iv “ trochlear nucleus LAT m lateral nucleus of the thalamus LES - lesion T/ro » nucleus dorsalis of the lateral geniculate body LGV m nucleus ventral!s of the lateral geniculate body NLF ■ medial longitudinal fasciculus MFD » nucleus mesencephalicus profundus dorsalis (deep reticular formation) PARF =* parafascicular nucleus POST * posterior nucleus of the thalamus PUL m pretectal area HR « red nucleus SN * substantia nigra PUL

PARF POST T 0/ MPD

0 f p U) \o bo

FIG. 9* A series of coronal sections through the caudal thalamus and the mesencephalon of an armadillo subjected to a small lesion of the most caudal pole of the neocortex. Degenerating fibers of passage and their endingB are shown as In Fig. 2.

CP ■ cerebral peduncle FX - fornix HIT m habenulo-interpeduncular tract LBS ■ lesion LGD - nucleus dorsalis of the lateral geniculate body LGV ** nucleus vent rails of the lateral geniculate body MSB ■ medial geniculate body LE

0 a HIV

4*" HI H U2

PIG. 10. Photomicrograph (a) illustrates degenerating fibers vithin the superior collicuius ipBilateral to a lesion vithin the caudal one-third (Fig. 8) of the neocortex. Photomicrograph (b) illustrates degen erating fibers vithin the stratum opticum (SO), the stratum griseum superficlalis (SgS), and vithin stratum griseum intermedlalls (Sgi) of the superior colliculus resulting from a lesion of the most caudal pole of the neocortex (Fig. 9 ). ^3

- v -sO.-* w ■ ■-,. * ■

[ -jTfcJ

* LITERATURE CITED

Altman, J. 1 9 6 2 Some fiber projections to the superior colliculue in the cat. J. Comp. Heur., 1 1 9:77-96.

Crosby, E. C., and J. W. Henderson 1948 The mammalian midbrain and isthmus regions. II. Fiber connections of the superior colllculus. B. Pathways concerned in automatic eye movements. J. Comp. Heur., 88:53-91*

Crosby, E. C., and R. Woodburn 1943 The nuclear pattern of the nontectal portions of the midbrain and Isthmus in the armadillo. J. Comp. Heur., 70:191-211.

Denny-Brown, D. 1 9 6 2 The midbrain and motor integration. Proc. Roy. 6 0c. Med., 55:527-530.

DeVito, J. L., and 0. A. Smith 1964 Subcortical projections of the prefrontal lobe of the monkey. J. Comp. Heur., 123:413-419.

Fisher, A. M., J. K. H&rting, 6. F. Martin, and M. I. Stuber 1969 T3ie origin, course and term J, nation of the corticospinal tract in the armadillo. J. Heur. Sic., 8:347-361.

Harting, J. K., and G. F. Martin (1 9 6) 9 Heocortical projections to ohb and medulla in the armadillo (Dasypus novemcinctus). ?In preparation.) Kuypers, H. G. J. M., and D. G. Lawrence 1 9 6 7 Cortical projections to the red nucleus and the brain stem in the rhesus monkey. Brain Research, 4:151-188.

Levin, P. M. 1936 The efferent fibers of the frontal lobe of the monkey (Macaca mulatta). J. Comp. Heur., 63:369-420.

Lui, C. N., and W. W. Chambers 1964 An experimental study of the corticospinal system in the monkey (Macaca mulatta). Die spinal pathways and preterminal distribution of degenerating fibers following discrete lesions of the pre- and post-central gyri and bulbar pyramid. J. Comp. Heur., 123:257-284.

Lund, R. D. 1 9 6 6 The occipitotectal pathway of the rat. J. Anat. (Lond.), 100:51-62.

Mabuchi, M., and T. Kusama 1 9 6 6 The corticorubral projection in the cat. Brain Research, 2:254-273- 4 4 *5 Martin, G. F, 1 9 6 8 The pattern of neocortical projections to the mesencephalon of the opossum (Dldelphls virginiana). Brain Research, 11:593-610.

Martin, I3. F., and A. M. Fisher 1 9 6 8 A further evaluation of the origin, the course and the termination of the opossum cortico spinal tract. J. Heur. Sci., 71177-187*

Martin, G. F., R. Bom, and M. I. Stuber 1 9 6 9 The rubrospinal tract of the opossum (Dldelphls virginiana). Anat. Hec., 163:226-227.

Meyers, R. E. 1963 Cortical projections to the mldbraln in the monkey. Anat. Rec., 1*5:337-338.

Nauta, 1W. J. H., and V. M. Bucher 195**- Efferent connections of the striate cortex in the albino rat. J. Comp. Neur., 100:257-285.

Nauta, W. J. H., and P. A. Gygax 195* Silver impregnation of degen erating axons in the central nervous system: a modified tech nique. Stain Tech., 29:91-93*

Nauta, W. J. H., and H. G. J. M. Kuypers 1958 Some ascending pathways in the brain stem reticular formation. In H. H. Jasper, L. D. Proctor, R. S. Knighton, W. C. No shay and R. T. Costello (eds.), Reticular Formation of the Brain, Little, Brown, Boston, Mass., p. 3*

Nyberg, Hansen, R., and A. Brodal 1963 Sites of termination of corti cospinal fibers in the cat. An experimental study with silver impregnation methods. J. Comp. Neur., 120:369-391*

Hyberg, Hansen, R., and A. Brodal 1 9 6* Sites and mode of termination of rubrospinal, fibers in the cat. An experimental study with silver impregnation methods. J. Anat. (Lond.), 98:235-253*

Papez, J. W. 1932 Thalamic nuclei of the nine-banded armadillo (Dab y pus novemcinctus). J. Comp. Neur., 56:*9-105*

Polrer, L. J., and G. Bouvler 1 9 6 6 The red nucleus and its efferent nervous pathways in the monkey. J. Comp. Neur., 128:223-2**.

Rinvik, E. 1 9 6 6 The cortico-nigral projections in the cat. An experi mental study with silver impregnation methods. J. Comp. Neur., 126:2*1-25*.

Rinvik, E., and F. Valberg 1963 Demonstration of a somatotopically arranged cortico-rubral projection in the cat. J. Comp. Neur., 121:393-*07.

Smith, G. E. 1899 The brain of Edentata. Trans. Linn. Soc., 2nd SerieB, Zool., 7:277-39** 46

Sprague, J. M. 1963 Corticofugal projections to the superior colliculus In the cat. Anat. Rec., 149:288.

Thompson, W. H. 1900 Degeneration resulting from lesions of the cortex of the temporal lobe. J. Anat. Physiol., 35:147-165.

Whitlock, D. 6., and W. J. H. Nauta 1936 Subcortical projections from the temporal neocortex in (Macaca mulatta). J. Comp. Neur., 106:182-2 1 2 . PART II

NEOCORTICAL PROJECTIONS TO OHE PONS AND MEDULLA IN THE

NINE-BANDED ARMADILLO (PASYPUS NOVEMCINCTUS)

^7 INTRODUCTION

Ifeocortical projections to the pons and medulla have been

investigated In several representatives of the mammalian line. The majority of these studies have been limited to the cat (Brodal et al.,

1956; Kuypers, 1956; Rossi and Brodal, 1956; Walberg, 1957; Kuypers,

1 9 5 8a; Brodal, 1 9 6) 8 and certain primates (Levin, 1936; Sunderland,

19^0; Hyby and Jansen, 1951; Whitlock and Nauta, 1956; Kuypers, 1958b;

DeVito and Smith, 1961*-; Shriver and Matzke, 1965; Kuypers and Lawrence,

1 9 6 7), although more recent work has been reported for the opossum

(Zimmerman and Chambers, 1963; Martin and West, 1 9 6; 7 Martin and King,

1 9 6 8), the rat (Torvik, 1956; Zimmerman and Chambers, 1963; Zimmerman

et al., 1 9 6U), the rabbit (Abdel-Kader, 1 9 6 8), the goat (Haartsen and

Yerhaart, 1 9 6), 7 and the tree shrew (Shriver and Noback, 1 9 6)* 7 In

these studies, particular emphasis was placed upon the neocortical

pathways to the basilar pontine gray, to certain brain stem sensory

nuclei and to the pontine and medullaxy reticular formation. Also,

considerable attention has centered around the question of whether or

not direct neocortical projections to brain stem motor nuclei exist in

subprimates.

Review of the pertinent literature indicates that such con

nections have not been described for any representative of the order

Edentata. The present study was undertaken to determine the

morphological substrate of neocortical influence on the more caudal

1*8 1+9 brain stem of the nine-banded armadillo, a member of the order Edentata.

It is hoped that the information gained from this and similar studies on still other representatives of different mammalian lines will emphasize the similarities of such connections within existing mammals and, perhaps Just aB importantly, point out possible differences in

such pathways. MATERIALS AND METHODS

Neocortical lesions vere placed in a rostral to caudal sequence in a total of 12 armadillos. While the majority of the ablations involved the cortex in close proximity to the only major neocortical sulcus, the supraorbital sulcus (Fig. l), smaller lesions vere placed in the most rostral (Fig. 11) and caudal poles (Fig. 13) of the neo cortex. One lesion involved the caudal one-third of the neocortex

(Fig. 13) t but did not extend as far caudally as the smaller lesion of the most caudal pole.

The animals vere allowed to survive for a period of 7-lA days.

They vere then sacrificed by perfusion with normal saline followed by buffered formalin, and the brains and spinal cords vere removed. Serial sections vere then cut on a freezing microtome and subsequently sub jected to the Nauta-Gygax technique (Nauta and Gygax, 195*0 f°r demon stration of degenerating axons. The limits of each lesion were defined histologically and any damaged white matter vas noted. Thionin-stained preparations of the armadillo brain vere used to help elucidate the cytoarchitecture of the brain stem. Wherever applicable, the termlnologr of OlszevBkl and Baxter (195*0 vas employed.

50 RESULTS

Hie results of this study will be described under the following three divisions: (a) projections of the neocortex rostral to the supraorbital sulcus, (b) projections of the neocortex immediately

caudal to the supraorbital sulcus, and (c) projections of the caudal one-third and moBt caudal pole of the neocortex.

Projections of the neocortex rostral to the supraorbital sulcus

Degenerating fascicles resulting from a small lesion of the most rostral pole of the neocortex (Fig. ll) coursed through the sub-

cortical white matter and into the anterior limb of the internal

capsule. These fibers then coursed caudally to assume a position

within the most ventral medial aspect of the ipsilateral cerebral

peduncle. At rostral pontine levels, degenerating fibers entered the

medial portion of the longitudinal pontine bundles and distributed to

the medial, the dorsal medial, and the ventromedial areas of the

basilar pontine gray (Figs. 11 and lUa). A few fibers crossed the

midline and ended within the ventral and medial areas of the contra

lateral pontine gray. While the predominant area of termination was

within the medial basilar pontine gray, scattered fibers also

terminated within the rostral limits of the superior central nucleus.

Corticopontine fibers resulting from this lesion coursed only as far

caudally as the rostral one-half of the basilar pontine gray.

51 52

3he results obtained from a brain subjected to a lesion of the mid-presupraorbital cortex (Fig. ll) indicate that this area of neo cortex projects to more caudal portions of the basilar pontine gray as opposed to the cortex of the rostral pole. In addition to projections vhich terminated in the basilar pontine gray, this mid-presupraorbital neocortex also distributed to certain midline and tegmental nuclei. At

rostral pontine levels, degenerating fascicles vere positioned vithln

the dorsal medial portion of the ipsilateral longitudinal pontine bundles and, at such levels, degenerating fibers terminated within the

dorsal-medial, medial and ventral medial areas of the basilar pontine

gray (Figs. 11 and l4b). Additional degenerating fascicles coursed

dorsally and terminated, at rostral pontine levels, in the superior

central nucleus and within the nucleus pontis centralis oralis

(Fig. ll). Some of these same fibers continued dorsally and terminated

within the nucleus of the dorsal raphe. At more caudal pontine levels,

the distribution of degenerating fascicles vaB more limited. Fibers

vere Judged to terminate within the dorsal-medial, the medial, and the

ventral medial areas of the basilar pontine gray. Additional fascicles

passed dorsally from the longitudinal pontine bundles and terminated

vithln the nucleus raphe pontis.

As reported in a previous study (Harting, 1 9 6), 9 degenerating

corticomesencephalic projections resulting from a lesion of the mid-

presupraorbital cortex terminated extensively within the ventral

nucleus of the periaqueductal gray. These degenerating fibers

terminated throughout the rostral-caudal extent of this mesencephalic 53 nucleus and coursed into the rostral pons to terminate within the lateral dorsal tegmental nucleus (Fig. ll).

One large ablation was placed immediately rostral to the supra orbital sulcus. Degenerating fibers resulting from this lesion followed a similar course through the rostral brain stem as did the projections from more rostral cortices. Degenerating fascicles vere located within the medial portion of the ipsllateral longitudinal pontine bundles and terminated vithln the dorsal medial, the medial, the ventral, and to a lesser degree, within the ventral lateral area of the pontine gray. Scattered fibers also passed dorsally and terminated within the superior central nucleus and more dorsally and laterally to terminate within the nucleus pontis centralis oralis.

Although technical problems vere encountered in the caudal brain stem sections, scattered preterminal and terminal degeneration was noted within the lateral parvocellular portions of the pontine and medullary reticular formation.

Projections of the neocortex immediately caudal to the supraorbital sulcus

Degenerating fibers resulting from leBions of the neocortex immediately caudal to the supraorbital sulcus (Fig. 12) coursed through the subcortical white matter and into the genu and posterior limb of the internal capsule. The majority of the degenerating fascicles eventually came to lie within the intermediate portion of the ipsilateral cerebral peduncle, a position which they generally maintained within the longitudinal pontine bundles. 5^ At roatral pontine levels, degenerating fibers terminated vithln the ventral, the ventral lateral, the dorsal lateral and the dorsal areas of the basilar pontine gray (Figs. 12 and 15a) • Scattered

fibers also passed dorsally from the main pathway to end within the

ipsilateral nucleus pontis centraliB oralis (Fig. 12) and at more

caudal levels vithln nucleus pontis centralis caudalis. At the level of

the motor nucleus of the facial nerve (Fig. 12), Injured fascicles

passed dorsally and laterally from the pyramidal bundle and terminated bilaterally vithln the nucleus reticularis gigantocellularis. Other

degenerating fibers passed uninterrupted through this nuclear area and

terminated bilaterally within the nucleus pontlB centralis caudalis,

extensively within the nucleus parvocellularis reticularis, and to a

limited extent, vithln pars oralis of the spinal fifth nucleus

(Fig. 12).

At rostral medullary levels (Fig. 12), degenerating fibers

coursed contralaterally and ipsilaterally from the pyramidal bundle

and terminated vithln the pars interpolaris of the spinal fifth

nucleus and within the hilum of that same nucleus (Fig. 12). At this

level the hilum area is designated as the caudal portion of the nucleus

parvocellularis reticularis. The amount of degeneration was greatest

vithln the ipsilateral hilum area and was confined mainly to the dorsal

portions of the ipsilateral nucleus of the spinal fifth tract.

Although the fiber degeneration vas more evenly distributed within the

contralateral spinal fifth nucleus, it did not distribute to the most

ventral portion of the nucleus. 55

At more caudal levels through the medulla (Fig. 12), degener ating fibers terminated within the contralateral pars caudalis of the spinal fifth nucleus and profusely within the area medial to that nucleus, previously designated as the hilum (Figs. 12 and 15b). At

this level, the hilum area is termed the subnucleus dorsalis of the

nucleus medulla oblongata centralis. Degenerating fibers also

terminated extensively within the hilum region ventral to the contra

lateral nucleus cuneatus, within the nucleus cuneatus itself (Figs. 12

and 15c) and within the nucleus of the solitary tract. This pattern of

degeneration, to the spinal fifth nucleus, the hilum area and to the

nucleus of the solitary tract, was similar on the ipsilateral side;

however, the amount of degeneration was considerably less. In addi

tion, scattered fibers terminated bilaterally within the inferior

olivary nucleus (Fig. 12).

At the level of the pyramidal decussation (Fig. 12), the dis

tribution of degenerating fibers was predominantly contralateral.

Degenerating fascicles terminated throughout the nucleus cuneatus,

within the dorsal two-thirds of the pars caudalis of the spinal fifth

nucleus, and profusely within the adjacent hilum area.

A prominent descending aberrant bundle of degenerating fibers

coursed caudally within the dorsal lateral pontine tegmentum on the

side of the lesion (Figs. 12 and 15d). These fibers left the cerebral

peduncle at caudal mesencephalic levels and were located at rostral

pontine levels, ventral and lateral to the mesencephalic root of five.

Although the majority of degenerating fibers within this bundle did not

terminate at these same levels, Borne were Judged to terminate within the dorsal lateral portion of the nucleus pontis centralis oralis. At mid-pontine levels the aberrant tract vaB located In and around the motor nucleus of the trigeminal nerve (Fig. 12). At that level,

scattered fascicles passed laterally from the aberrant bundle and

terminated within the medial aspect of the pars oralis of the spinal

fifth nucleus. At the level of the motor nucleus of seven fibers

coursing in this bundle terminated within the lateral parvocellular

pontine reticular formation, where they became intermixed with degen

erating transtegmental fibers from the ipsilateral pyramidal bundle.

Caudal to this level, fibers of the mesencephalic aberrant bundle

could not be distinguished from degenerating fibers which passed from

the ipsilateral pyramidal tract and terminated within the lateral

reticular formation.

Pro.jections of the caudal one-third and most caudal pole of the neocortex

Degenerating fibers resulting from a lesion of the caudal one-

third of the neocortex (Fig. 13) were followed through the caudal part

of the internal capsule and into the intermediate and lateral aspects

of the ipsilateral cerebral peduncle. These fibers maintained that

position within the rostral portion of the longitudinal pontine bundles

and terminated, at rostral pontine levels, within the ventral and

lateral areas of the basilar pontine gray. More caudally, degenerating

fibers were positioned throughout the longitudinal pontine bundles and

terminated within the ventral, the ventral lateral, and the lateral

baBilar pontine gray (Figs. 13 and l^c). At the level of the motor

root of the trigeminal nerve (Fig. 13), degenerating fascicles 57 terminated vithln the dorsal lateral, the lateral, and the ventral lateral areas of the basilar pontine gray (Fig. 13). Degenerating fibers from this lesion did not course caudal to the trigeminal complex.

Neocortical fibers emanating from the most caudal pole of the neocortex, upon reaching pontine levels, vere located vithln the most lateral portion of the Ipsilateral longitudinal pontine bundles

(Fig. 13). At rostral pontine levels, degenerating fibers terminated extensively vithin the lateral basilar pontine gray (Figs. 13 and l^d), and to a lesser degree, vithln the ventral basilar pontine gray. At slightly more caudal pontine levels, the main area of fiber termination was vithin the lateral and ventral lateral areas of the ventral basilar pontine gray. Degenerating fibers resulting from this lesion did not course further caudally than the rostral one-half of the basilar

pontine gray. DISCUSSION

Hie neocortical projections to the pons and medulla will be discussed under the following three divisions: (a) corticopontine projections, (b) cortlcoretlcular projections and (c) corticofugal projections to brain stem sensory nuclei.

Corticopontine projections

All areas of the neocortex leBioned in the present study projected to the basilar pontine gray. A pattern of cortical origin and pontine termination of these projections was apparent in the armadillo. Hie neocortex rostral to the supraorbital sulcus distributed to the dorsal-medial, the medial, and the ventral-medial areas of the basilar pontine gray. The neocortex immediately caudal to the supra orbital sulcus projected degenerating fascicles to the ventral, the ventral-lateral and to the dorsal-lateral areas of the basilar pontine gray; whereas the more caudal neocortices projected to the dorsal- lateral, the lateral, and to the ventral lateral pontine gray.

With regard to the corticopontine projections from cortices

rostral to the Bupraorbital sulcus, specific differences in termination vere noted, depending upon the location of the lesion. Corticopontine

projections emanating from the most rostral pole of the neocortex

distributed to only the rostral portions of the pontine gray. In

comparison, degenerating fascicles resulting from lesions of the

58 59 mid-presupraorbital neocortex terminated throughout the rostral-caudal limits of the pre-trigeminal basilar pontine gray. The pattern of corticopontine distribution resulting from a lesion of the neocortex imediately rostral to the supraorbital sulcus vas similar to that of more rostral cortices. In addition to its medial projections, this area of neocortex also projected to the dorsal and lateral pontine gray.

These results, concerning corticopontine pathways from more

rostral cortices in the armadillo, are similar to those described for

the opossum (Martin and King, 1 9 6) 8 and the monkey (Levin, 1936;

Sunderland, 1940; Nyby and Jansen, 1951; DeVito and Smith, 1964). In

both the opossum and the monkey, corticopontine fibers resulting from

lesions of rostral neocortical areas projected to the dorsal, the

medial, and the ventral basilar pontine nuclei. In the rabbit (Abdel-

Kader, I960), however, degenerating corticopontine fibers resulting

from lesions of the rostral one-third of the neocortex distributed to

the dorsal medial, the dorsal and to the dorsal lateral areas of the

basilar pontine gray. The dorsal mediaLarea of pontine gray, in the

rabbit, is designated nucleus reticularis tegmenti according to the

nomenclature of Brodal and Jansen (1946).

The neocortex immediately caudal to the supraorbital sulcus

projected to the ventral, ventral-lateral, and dorsal-lateral pontine

gray. This pattern is similar to that described for the monkey (Hyby

and Jansen, 1951)* Corticopontine projections resulting from lesions

of the granular, post central cortices of the monkey terminate in the 6o ventral and lateral areaB of the basilar pontine gray. This same area of neocortex in the monkey projected to certain sensory nuclei of the pons and medulla (Bee Kuypers and Lawrence, 1967* for review). It Is interesting to note that the neocortex lnmediately caudal to the supraorbital sulcus in the armadillo also projected to these same sensory nuclei. Although these two neocortical areas have similar efferent projections, neither cytoarchitectonic or stimulation studies have been accomplished on the armadillo neocortex which would enable a valid comparison of the two neocortical areas.

Degenerating projections to the lateral and ventral-lateral basilar pontine gray resulted from lesions of both the caudal one- third and caudal tip of the neocortex. Hie lack of cytoarchitectural evidence does not facilitate defining these areas in the armadillo as peristriate and/or striate. However, the projections emanating from these areas are quite similar to the occlpltopontlne projections described in various mammals, especially the opossum (Martin and King,

1 9 6 8), the rabbit (Abdel-Kader, 1 9 6 8), and the monkey (Hyby and Jansen,

1951 j Whitlock and Jfauta, 1 9 5 6). In the rhesus monkey, however, occlpltopontlne fibers did not terminate vithin the ventral pontine gray as described for the opossum and as now described in the armadillo. Occlpltopontlne connections in the rabbit (Abdel-Kader,

1 9 6 8) also differ slightly from that described in the opossum and armadillo in that degenerating fibers, in addition to terminating vithin the lateral and ventral areas of pontine gray, terminate vithin the dorsal lateral rontine gray. Borne of the degenerating 6l fiberB which resulted from the lesion of the caudal one-third of the neocortex may have arisen from regions comparable to "temporal" or

"striate" cortex. Considerable white matter was undercut In this

lesion and fibers emanating from the more ventral lateral areas of the neocortex may have been Interrupted. Although the existence of

temporopontine fibers has been disputed for the cat (Kusama et al.,

1 9 6 6), such fibers have been reported to terminate in the ventral and

lateral pontine gray in the opossum (Martin and King, 1 9 6) 9 and in the

lateral pontine gray in the rabbit (Abdel-Kader, 1968) and monkey

(ityby and Jansen, 1951 and Whitlock and Nauta, 1 9 5 6).

Corticoretlcular projections

Projections to the pontine and medullary reticular formation

of the armadillo vere found to arise from the neocortex rostral and

Immediately caudal to the supraorbital sulcus. Degenerating cortlco-

reticular fibers did not result from lesions of more caudal cortlceB.

In general, lesions of the neocortex rostral to the supraorbital sulcus

produced fiber degeneration which distributed mainly to the medial

reticular formation of the rostral and intermediate pontine tegmentum.

Degenerating corticoretlcular projections resulting from a

lesion of the frontal pole of the neocortex were limited to a few

scattered fibers which terminated within the rostral limits of the

superior central nucleus. This pattern is in general agreement with

studies reported for the tree shrew (Shriver and Hoback, 1 9 6) 7 in which

corticoretlcular projections from frontal cortex were relatively sparse

and quite limited In their distribution when compared with other areas 62 of neocortex giving rise to corticoretlcular projections. Cortico retlcular pathways resulting from a lesion of the mid-presupraorbital cortex terminated vithin the medial portions of the reticular formation throughout the rostral one-third of the pontine tegmentum. This

Included projections to the superior central nucleus, the nucleus raphe pontis, the nucleus pontis centralis oralis, and to the nucleus of the dorsal raphe. These findings partially agree with studies done on the rat (Valverde, 1 9 6), 2 cat (Kuypers, 1958a ), tree shrev (Shriver and

Noback, 1 9 6 7), and monkey (Kuypers, i9 6 0) in vhich rostral neocortical areas distributed corticoretlcular fibers to the medial reticular formation of the caudal brain stem.

The neocortex imnediately caudal to the supraorbital sulcus distributed extensively to the lateral pontine and medullary reticular formation. At rostral pontine levelB, degenerating fibers terminated vithin the ipsilateral nucleus pontis centralis oralis. At the level of the motor nucleus of the facial nerve, degenerating fibers terminated bilaterally vithin the nucleus reticularis glgantocellularis, the nucleus pontis centralis caudalis, and most extensively vithln the nucleus parvocellularis reticularis. This bilateral pattern of distri bution of degeneration continued caudally into the medulla vhere the main area of termination vas vithln the subnucleus dorsalis of the nucleus medullae oblongatse centralis. However, at more caudal brain stem levels the contralateral projections vere significantly more numerous than the ipsilateral distribution.

The profuse degeneration vithln the lateral parvocellular portion of the reticular formation resulting from lesions of the neocortex immediately caudal to the supraorbital sulcus is quite similar to the pattern of fiber degeneration resulting from lesions of the sensory cortex in the tree shrew (Shriver and Hoback, 1 9 6). 7

However, it should be emphasized that in the armadillo, no cytoarchitectural or neurophyBiological evidence is available to substantiate calling this area of cortex “sensory cortex," as waB done for the tree shrew. Studies in the rat (Valverde, 1962), the monkey (Kuypers,

1958b), and chimpanzee (Kuypers, 1958b) indicate that sensory cortex in these mammals distributed corticoretlcular fibers that terminated primarily within the contralateral lateral parvocellular reticular formation.

It was observed that in the armadillo, certain corticoretlcular projections passed through, or in very close proximity, to motor nuclei of cranial nerve located in the pons and medulla. However, none of these fibers were Judged to terminate within these nuclei. It is probably via the "internuncial pools" of neurons (Kuypers, 1958a K located within the surrounding lateral reticular formation, that some degree of cortical regulation over the lower motor neurons within these cranial nerve motor nuclei is attained. Studies done on the rat

(Valverde, 1962; Zimmerman et al., IS>64) and the cat (Kuypers, 1956)

Indicate that after lesions of motor cortices profuse corticoretlcular projections terminated within these lateral internuncial pools.

Further support for this hypothesis is found in Golgi studies

(Scheibel, 1955; Valverde, 1 9 6 2) done on the cat brain which indicate

that the neurons of the lateral reticular formation possess axons which are in synaptic contact vith motor neurons of cranial nerve motor nuclei.

Corticofugal projections to sensory relay nuclei

The present study indicates that degenerating fibers originating from the neocortex immediately caudal to the supraorbital sulcus

terminated in all subdivisions of the spinal trigeminal nucleus, in the nucleus of the solitary tract, and vithin the nucleus cuneatus. The

scattered fibers vhlch projected to subnucleus oralis of the spinal

fifth nucleus were ipsilateral, vhereas the subnucleus interpolaris

received a bilateral distribution of degenerating fascicles. The most

extensive projections vere to the subnucleus caudalis and although the

distribution to this area vas bilateral, a contralateral predominance vas evident at the level of the pyramidal decussation. Projections to

the nucleus cuneatus and the nucleus of the solitary tract vere also

bilateral, although the contralateral nuclei received a significantly

greater distribution of degenerating corticofugal fibers.

Neocortical projections to brain stem sensory nuclei have been

described in both subprimate (the opossum, Martin and West, 1967; the

rat, Torvik, 1956 and Zimmerman et al., 196k; the goat, Haarsten and

Verhaart, 1967 and the cat, Brodal et al., 1956) and primate forms (the

tree shrev, Shriver and Noback, 1 9 6; 7 the marmoset monkey, Shriver and

Matzke, 1 9 6; 5 the rhesus monkey, Kuypers, 1958b sad Liu and Chamber,

1 9 6k and the chimpanzee, Kuypers, 1958b). In the opossum (Martin and

West, 1 9 6) 7 and in the tree shrev (Shriver and Noback, 1 9 6) 7 auch

projections to brain stem sensory nuclei are mainly contralateral and arise from the somatic motor-somatic sensory amalgam In the opossum, and from the spatially separate sensory and motor cortex In the tree shrev. In the armadillo, the projections to brain stem sensory nuclei arise from the Immediate postsupraorbltal neocortex and, In comparison

to the opossum and the tree shrev, distributed a greater number of degenerating fibers to Ipsilateral brain stem sensory nuclei. Hovever,

it should be emphasized that, in most areas, the contralateral projec

tions vere most numerous. This contralateral predominance of cortlco-

fugal projections to brain stem sensory nuclei exists for the majority

of mammals thus far reported.

Differences also exist in the origin of certain aberrant bundles

described for the opossum, the tree shrev, the goat and nov for the

armadillo. A contralateral aberrant bundle vas described for the

opossum. This bundle vas composed of descending fibers vhich passed

dorsal-laterally from the ipsilateral pyramidal bundle at pontine levels

and recurrent fibers vhich, after crossing vithln the pyramidal decussa

tion coursed rostralvard to their termination. These aberrant fibers

coursed in a position immediately dorsal to the spinal fifth tract and

distributed to the spinal fifth nucleus and the dorsal column nuclei. A

similar contralateral aberrant bundle, arising from the somatic sensory

cortex, vas described for the tree shrew. Shriver and Hoback (1 9 6) 7

interpreted this bundle as being composed of recurrent pyramidal fibers

because the degenerating fibers contained vithin this bundle vere

larger and more numerous at caudal brain stem levels, than vas the case

at more rostral levels. The aberrant bundle in the armadillo is an ipsilateral projection composed of degenerating fibers vhich passed dorsal laterally from the cerebral peduncle at caudal mesencephalic levels. These fibers then coursed caudally vithin the dorsal lateral pontine tegmentum. In contrast to the recurrent pyramidal fibers described for the tree shrev* the fibers contained vithin the aberrant bundle in the armadillo vere larger and numerous at rostral pontine levels and significantly smaller and less numerous at more caudal brain stem levels. This bundle in the armadillo is similar to the ipBilat- eral aberrant bundle described for the goat (Harrsten and Verhaart,

1 9 6). 7 Hovever, in the goat, this bundle distributed to more caudal ipsilateral brain stem levels than did the aberrant bundle in the armadillo.

It haB been demonstrated by neurophysiological methods (Kruger and Michel, 1 9 6 2) that fibers of the mandibular division of the trigeminal nerve terminate vithin the dorsal portion of the spinal nucleus, vhereas fibers of the ophthalmic division terminate most ventrally. The results of this study indicate that, vhile there is significant cortical input into the mandibular and maxillary divisions of the spinal fifth nucleus, there is relatively little distribution into the ophthalmic division. This pattern seems logical if one com pares the large extent of the mandibular and maxillary regions vith the relatively small ophthalmic region in the armadillo.

The results of an earlier study in the armadillo (Fisher et

al., 1 9 6) 9 indicated that corticospinal fibers arose from the neocortex

immediately rostral and caudal to the supraorbital sulcus and coursed 67 only as far caudally as mid-thoracic spinal cord levels. Studies done on the rat (Zimmerman et al., I96U), the cat (Kuypers, 1956a) and the monkey (Liu and Chambers, 196k) indicated that forelimb areas of the neocortex projected fibers predominantly to cervical cord levels. This same cortical area also projected numerous fibers to the nucleus cuneatus. Therefore, it is apparent that the same area of neocortex vhich projected corticospinal fibers to cervical cord segments also distributed fibers to sensory nuclei receiving afferent projections from the upper limb. The presence of corticospinal projections to those spinal cord levels concerned with innervation of the forelimbs in the armadillo (Fisher et al., 1 9 6 9); the lack of such projections

to cord levels concerned with Innervation of the hindlimb, offers a possible explanation for the extensive projections to nucleus cuneatus and the lack of such projections to nucleus gracilis. SlftMAKY

Hie results of this study indicate that, in the nine-handed armadillo, the pre-trigeminal basilar pontine gray receives neocortical input from a considerable portion of the neocortex. Degenerating fibers resulting from a lesion of the frontal tip of the neocortex terminated vithin the dorsal medial and medial areas of the rostral basilar pontine gray. Corticopontine fibers emanating from the mid- presupraorbital neocortex ended throughout the rostral to caudal extent of the basilar pontine gray, and terminated vithin the dorsal medial, medial, and the ventral medial areas; whereas degenerating fibers resulting from a lesion of the neocortex immediately rostral to the supraorbital sulcus terminated vithin the medial, the ventral and the ventral lateral areas of the basilar pontine gray. The neocortex imme diately caudal to the supraorbital sulcus distributed corticopontine fibers to the dorsal lateral, the ventral lateral, and the ventral areas of the basilar pontine gray, vhile degenerating fibers resulting from lesions of the caudal one-third and most caudal tip of the neocortex projected to the ventral and lateral portions of the basilar pontine gray.

Neocortical projections to the pontine and medullary reticular formation originated mainly from cortical areas rostral and immediately caudal to the supraorbital sulcus. The neocortex rostral to the supraorbital sulcus distributed to the rostral and medial portions of the pontine reticular formation, whereas corticoretlcular fibers from 68 the neocortex Immediately caudal to the supraorbital sulcus projected profusely to the lateral areas of both the pontine and medullary reticular formation. This same area of neocortex, caudal to the supra orbital sulcus, also distributed degenerating fascicles to the spinal trigeminal nucleus, the nucleus of the solitary tract and to the nucleus cuneatns. Ho degenerating fibers were seen to terminate within motor nuclei located within either the ponB or medulla. 70

FIG. 11. A serieB of coronal sections through the roBtral pons of an armadillo subjected to a lesion of the most rostral tip of the neocortex (left). A aeries of coronal sections through the rostral and intermediate pons of an armadillo subjected to a lesion of the mid-presupraorbital neocortex (right). Degenerating fiberB of passage and their endings are indicated as in Fig. 2.

IC m inferior colliculus IDT » lateral dorsal tegmental nucleus LES a lesion MLF a medial longitudinal fasciculus MNV ■ motor nucleus of five MR * mesencephalic root of five POO > nucleus pontls centralis oralis BP a nucleus raphe pontis SC a superior central nucleus STY a spinal tract of five 71

LE LE n

MR O 9 S^p^-DT MLF i " Roo

•RP

_ o

MNV 72

PIG. 12. A series of coronal sections through the pons and medulla of an armadillo subjected to a lesion of the neocortex Immediately caudal to the supraorbital sulcus. Degenerating fibers of passage and their endings are indicated as in Fig. 2.

CRD m subnucleus dorsalis of the nucleus medullae oblongatae centralis GC - nucleus reticularis gigantocellularis IOH ■ inferior olivary nucleus LES m lesion ML - medial lemniscus MLF ■ medial longitudinal fasciculus MNV - motor nucleus of five ME *» mesencephalic root of five EC ■ nucleus cuneatus NG « nucleus gracilis UTS - nucleus of the solitary tract PC - nucleus parvocellularis reticularis POC m nucleus pontls centralis caudalis POO * nucleus pontls centralis oralis SNV b spinal nucleus of five STV m spinal tract of the five TS ■ solitary tract X * dorsal vagal nucleus VII * motor nucleus of seven XII b hypoglossal nucleus

FIG. 1 3. A series of coronal sections through the rostral and Intermediate pons of an armadillo subjected to a lesion of the caudal one-third of the neocortex (left). A series of coronal sections through the rostral pons of an armadillo subjected to a lesion ~ of the most caudal pole of the neocortex (right). Degenerating fibers of passage and their endlngB are indicated as in Fig. 2.

IC - inferior collicuius UBS - lesion MLF - medial longitudinal fasciculus MRV ■ motor nucleus of five STV ■ spinal tract of five 0

'MNV l-

vn-4 76

FIG. 1^. Photomicrograph (a) Illustrates degeneration vithin the medial basilar pontine gray resulting from a lesion of the most rostral pole of the neocortex. Photomicrograph (b) Illustrates degeneration within the medial basilar pontine gray resulting from a lesion of the mid-presupraorbital neocortex. Photomicrograph (c) illustrates degeneration within the ventral lateral basilar pontine gray as a result of a lesion of the caudal one-third of the neocortex. Photomicrograph (d) illustrates degeneration within the lateral basilar pontine gray resulting from a lesion of the most caudal pole of the neocortex. Ifauta-Gygax technique.

FIG. 15. Photomicrographa illustrating degeneration vithin the ipsilateral ventral basilar pontine gray (a), vithin the contralateral hilum area and spinal fifth nucleus (b), and vithin the ventral portion of the contralateral nucleus cuneatus (c), as a result of a leBlon immediately caudal to the supra orbital sulcus. Photomicrograph (d) Illustrates the bundles of degenerating fibers contained vithin the Ipsilateral aberrant bundle resulting from the same Immediate post-supraorbital lesion. Nauta- Gygax technique. I I 6V &

• . C- JCi.-- J W . ' ’

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