THE CEREBELLUM 661 



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

 by narrow antl rehitively deep sulci, many of which a])proach a transverse (hrection. 

 Certain of the sulci are more pronounced than the otiiers, and l\v 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 lol)os of the vermis arc readily distinguishod on a median section. Enumerated from 

 the anterior to the i)osterior extremity they are: (1) Hngula, (2) lohus centraHs, CA) lohiLs aseendens, 

 (4) lohus oulminis, (.">) lohus clivi, ((i) tuher vermis, (7) pyramis, (S) uvula, (()) nodulus. Each 

 hemisphere is cut into laterally by two sulci which mark off two sagittal di.scoid masses, termed by 

 Ziehen tabulations. The external tabulation 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. 

 Tn the absence of a satisfactory morphological basis it seems undesirable to deal with the lobation 

 of the cereljcllum in further detail. 



The cerebellar peduncles, three on each side, join the central white matter of 

 the cerebelhnn at the l)ase. The posterior peduncle is the restiform body 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 

 cerebellum. The middle peduncle is formed, as ]ireviou.sly seen, l^y the brachium 

 pontis. The anterior peduncles (Brachia conjunctiva) pa.ss forward on either side 

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

 the fourth ventricle. They disappear under the corpora quadrigemina into the 

 substance of the mid-brain. At the point of disappearance the trochlear (fourth) 

 nerve emerges from the mid-brain. In some cases two or three bundles of fibers 

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

 curve obliquely forw^ard and downward over the outer aspect of the latter, and 

 spread out on the ventral face of the cerebral peduncle just in front of the pons. 



On sagittal section the cerebellum is seen to consist of a layer of cortical gray 

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

 consists of a large basal mass (Corpus medullare), which is joined l)y the pedimcles, 

 and gives off primary laminae 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 "arbor vitae" 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 cerel)ellum are as 

 follows: The posterior peiluncle (Corpus restiforme) is composed of afferent and efferent fillers 

 wliicli coini(>ct the ccrclicllum with the medulla and spinal cord. The cerebello-spinal fascicu- 

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

 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 cerel)cllar cortex. Olivo-cerebellar fibers 

 (chiefly afferent) connect with the olivary nucleus of the same and of the opposite side of the me- 

 dulla oblongata. The nucleo-cerebellar fasciculus comprises fibers deri\-ed frf)in 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 tli(> spinal 

 cord. The chief iacts concerning the middl(> peduncle have been mentioned in the d<>scription 

 of the pons. The anterior peduncle is essentially an elT(>rent tract, the fibers of whicli pass for- 

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

 After the peduncles disappear under the corpora (|uadrigemina, they converge and many of their 

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

 fibers end in the nucleus ruber. Thence impulses arc ti'ansmitted in two directions: first, by 

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

 brain-stem and lateral cohunns of the cord to the ventral horn cells, Th(> ventro-lateral cere- 

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

 the cerel)ellum. Its fibers appear to be axones of cells of the posterior horns of the cord; they 

 pa.ss 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. 



