274 THE NERVOUS SYSTEM 



The Cerebellum. 



Anatomy. The cerebellum, or little brain (see Fig 79), is 

 situated beneath the occipital lobes of the cerebrum, weighs 

 some 5 J ounces in the male to 4^ ounces in the female, and con- 

 sists of a central and two lateral lobes. It is composed of white 

 and gray matter, the latter being, with the exception of the corpora 

 dentata in the lateral lobes, situated externally. The convolu- 

 tions on its surface are much finer than are those on the cerebral 

 surface. It is separated from the parts above by the tentorium 

 cerebelli, a process of the dura mater. 



Fibers. The fibers passing away from the cerebellum are col- 

 lected into three bundles on each side, known as the superior, 

 middle and inferior peduncles. The superior peduncle has a 

 direction forward and upward to reach the crus and optic thala- 

 mus; fibers in it connect the cerebellum with the cerebrum. 

 Certain of these decussate underneath the corpora quadrigemina 

 with corresponding fibers from the opposite side, so that each 

 side of the cerebellum is connected with both sides of the cere- 

 brum. Attention has been called to fibers passing down from 

 the cerebrum through the pons to the cerebellum. Fibers in the 

 middle peduncle connect the two lateral halves of the cerebellum 

 through the pons. Fibers in the inferior peduncle are continuous 

 below with fibers in the posterior columns of the cord through 

 the restiform bodies of the medulla. 



Function. The only characteristic phenomenon invariably 

 following removal of the cerebellum is an inability to coordinate 

 the voluntary muscular movements. The foot, for example, can be 

 raised, and the voluntary muscular act concerned in raising it 

 may be as vigorous as ever, but the animal cannot so govern his 

 movements as to know where he put it down. Even the coordin- 

 ation necessary in standing is lost, and the maintenance of the 

 equilibrium is very difficult, if not impossible. The so-called 

 muscular sense is abolished, and, while the power to contract 



