92 ANATOMY OP THE HEAD AND NECK. 



By drawing back the cerebellum two large white core 

 will be seen extending from the corpora quadrigemina t( 

 the cerebellum ; these are termed the processus e cerebelh 

 ad testes, or superior peduncles of the cerebellum. Betweei 

 them is stretched a thin layer of cerebral substance, covei 

 ing in the passage from the third to the fourth ventricle, 

 well as a part of the fourth ventricle itself; this is the vali 

 of Vieussens. 



CEREBELLUM. 



The cerebellum is to be detached from the remains of the cerebrni 

 by carrying the knife through the optic thalami, so that the cert 

 bellum, with the corpora quadrigemina, pons Varolii, crura cerebi 

 and medulla oblongata, shall remain united together. 



The CEREBELLUM, or little brain, lies beneath the posl 

 rior lobes of the cerebrum, from which, in the cranial cavit; 

 it is separated by the ten tori urn; its diameter is greatest 

 from side to side, and it is incompletely divided into twc 

 lateral hemispheres. Its surface is marked by plates 01 

 laminae instead of convolutions, and between these ai 

 fissures lined by pia mater ; the deeper of these fissui 

 break the hemispheres into imperfectly marked lobes. 



The two hemispheres are united on the upper or cerebrt 

 aspect by a central, constricted isthmus, called the superic 

 vermiform process; in front of this is a notch which ei 

 circles the corpora quadrigemina posteriorly, called im 

 sura cerebelli anterior; behind the isthmus is anothi 

 notch called incisura cerebelli posterior. Upon the und( 

 surface of the cerebellum the depression which receivi 

 the medulla oblongata is called the vallecula, and at the 

 bottom of this is an isthmus, corresponding to that coi 

 necting the hemispheres on the superior surface, and calle< 

 the inferior vermiform process. 



The cerebellum is united to the rest of the encephalon 

 by a large stalk-like process on each side. This process 

 subdivides into three rounded cords, called peduncles. The 

 superior peduncle, or processus e cerebello ad testes, is 

 directed forward to the corpora quadrigemina, and forms 

 the anterior part of the lateral boundary of the fourth 

 ventricle; between these peduncles is the valve of Vieussens. 

 The middle peduncle, or processus ad poritem, is commonly 

 called the cms cerebelli, and is the largest of the three 

 peduncles. Its fibres begin in the lateral part of the cere- 

 bellum, and are directed forward to the pons Yarolii, of 



