THE CEREBELLUM 661 



The surface of the eerelieUum is further cut up into numerous gyri or folia 

 by narrow anil relatively deep sulci, many of which approach a transverse direction, 

 Certain of the sulci are more pronounced than the others, and by means of them it 

 is possible to define groups of gyri. Such groups are termed lobes, and have 

 received specific names, derived chiefly from the systematic descriptions of the 

 human cerebellum. 



Tlio lohos of the vorniis arc roaflily distinguishcMl on a median section. Enumerated from 

 the anterior to the posterior (>xtremity they are: (1 ) Hnguhi, (2) lobus centralis, (o) lobus ascendens, 

 (4) lol)iis cuhninis, (."}) lohus cHvi, ((») tul>er vermis, (7) pyramis, (S) uvuUi, (9) nodulus. Each 

 hemisphere is cut into laterally by two sulci which mark ofT two sagittal discoid masses, termed by 

 Ziehen tal)ulations. The external tabuhition consists of four or five lobules, the lowest of which 

 is regarded as the flocculus. The inner part of the hemisphere is divided into three or four lobes. 

 In the absence of a satisfactory morphological ba.sis it .seems undesirable to deal with the lobation 

 of the cerei)elluni in further detail. 



The cerebellar peduncles, t]ir(>e on cacli sid(\ join the central white matter of 

 the cereljciluin at the liasc. The posterior peduncle is the restiform bod}' of the 

 medulla, a large rounded tract derived from the lateral and ventral columns of 

 the cord. Near the middle of the medulla it inclines outward, forms the lateral 

 wall of the fourth ventricle, and ends by entering the central white matter of the 

 cer('l)ellum. The middle peduncle is formed, as jireviously seen, by the ])rachium 

 pontis. The anterior peduncles (^iirachia conjunctiva) pass forward on either side 

 on the dorsal surface of the pons, forming the lateral boundary of the fore part of 

 the fotirth ventricle. They disappear imder the corpora quadri<2;emina into the 

 sul)stance of the mid-brain. At the ])()int of disai)pearance the trochlear (fotirth) 

 nerve emerges from the mid-brain. In some cases two or three bundles of fi}:!ers 

 (Fila lateralia pontis) arise in the angle between the middle and anterior peduncle, 

 curve obliquely forward and downward over the outer aspect of the latter, and 

 spread out on the ventral face of the cerel)ral peduncle just in front of the pons. 



On sagittal section the cereb(>llum is seen to consist of a layer of cortical gray 

 matter (Substantia corticalis) and the medullary white matter. The white matter 

 consists of a large basal mass (Corpus meduUare), which is joined by the peduncles, 

 and gives off primary laminte to the lobules; from these secondary and tertiary 

 laminae arise, the latter entering the gyri. The arrangement on sagittal section is 

 tree-like, hence the classical term "arl)or vitse" which is applied to it. The central 

 gray matter consists of groups of cells which form small nuclei embedded in the 

 central white substance. 



As noted above the central gray matter does not form a large nucleus, the corpus dentatum, 

 which is so conspicuous an object on sagittal sections of the cerebellar hemisphere in man. 



The principal connections established by the peduncular fibers of the cerebellum are as 

 follows: The posterior peduncle (Corpus restiforme) is composed of afferent antl efferent fibers 

 which connect the cereliellum with the medulla and spinal cord. The cerebello-spinal fascicu- 

 lus or direct cerebellar tract, which arises from the cells of the nucleus dorsahs (Clarke's column) 

 of the cord, ends in the cortex of the vermis; many of its fibers cross to the opposite side. 

 Numerous arcuate fibers from the nucleus gracilis and nucleus cuneatus of the same and op- 

 posite sides establish connections with cells of the cerebellar cortex. Olivo-cerebellar fibers 

 (chiefly afferent) connect witli the olivary nucleus of the same and of the opposite side of the ine- 

 dulla oblongata. The nucleo-cerebellar fasciculus comprises fillers derived from the nuclei of 

 the fifth, eighth, and tenth cranial nerves (Edinger). The descending cerebello-spinal fascicu- 

 lus consists of fibers which terminate in relation with cells of the ventral horns of the spinal 

 cord. The chief facts concerning the middle peduncle have been mentioned in the description 

 of the pons. The anterior peduncle is essentially an efferent tract, the fibers of which pass for- 

 ward to the tegmentum of the cerebral peduncle, the subthalamic region, and the thalamus. 

 After the peduncles disappear uncler the corpora quadrigemina, they converge and many of their 

 fibers intercross, forming the decussation of the superior peduncle. A considerable number of 

 fibers end in the nucleus ruljer. Thence impulses are transmitted in two directions: first, by 

 thalamo-cortical fibers to the cerebral cortex; second, by the rubro-spinal tract through the 

 brain-stem anrl lateral columns of the cord to the ventral horn cells. Tiie ventro-lateral cere- 

 bellospinal fasciculus (Cowers' tract) is an ill-defined tract which connects the spinal cord with 

 the cerebellum. Its fibers appear to be axones of cells of the posterior horns of the cord; they 

 pass in the lateral column of the cord, become scattered in passing through the reticular forma- 

 tion of the medulla and pons, and enter the cerebellum by way of the anterior medullary velum. 



