318 



ANATOMY OF THE CENTEAL NEBTOUS SYSTEM. 



3. Lobus cuneiformis, lying external to the tonsilla. 



4. Lobus posterior inferior, the anterior portion of which is called the 

 lobus gracilis and the posterior portion the lobus semilunaris inferior. 



In Fig. 205 one may see on either side the three medullary processes, 

 or commissures, which pass to the cerebellum. The fibers of these commis- 

 sures pass into the central white substance of the hemispheres, thence into 

 the medullary portion of the individual lobes, whence they extend into the 

 lobules and ridges. These ridges are covered with gray cortex which every- 

 where follows the conformation of the medullary substance and thus gains 

 an extension which is greater than the outer form and size of the cerebellum 

 would lead one to expect. 



The white substance of the hemispheres is considerable in quantity. 



Fig. 205. — The tliree pairs of cerebellar pedunclQS. 8, Corpora quadri- 

 gemina. 5, Anterior cerebellar peduncle. 7, Middle cerebellar peduncle, or 

 Brachium pontis. 3, Posterior cerebellar peduncle. 1, Fossa rhomboidalia. 2, 

 Strise acusticse. 6, Fillet. (After Hirschfeld and Leveillg.) 



The accompanying sagittal section of the cerebellum passes through the 

 center of the vermis (Fig. 206). It shows how the medullary substance is 

 continuous anteriorly with the velum medullare anticum, which extends as 

 a thin membrane toward the corpora quadrigemina. This thin membrane, 

 stretched between the anterior peduncles, forms a transition from the roof of 

 the mesencephalon to the roof of the metencephalon. Upon it lies the 

 most anterior lobule of the superior vermiform process: the lingula. 



The peculiar picture presented by the longitudinal section of the vermis 

 has, from time immemorial, borne the name arbor vitce. The central por- 

 tion of the medullary part is called the corpus trapezoides. Into this there 



