THE CEREBELLUM 561 



omo-hyoid through its descending branch, descendens noni; the thyro-hyoid 

 through a special branch; and the genio-hyoid, stylo-glossus, hyo-glossus, 

 and genio-hyo-glossus and linguales through its lingual branches. 



Functions. The function of the hypoglossal is exclusively motor. In 

 cases of hemiplegia involving the functions of the hypoglossal nerve the tongue 

 when protruded deviates toward the paralyzed side, when withdrawn it turns 

 away from the paralyzed side. Occasionally it is not possible to observe any 

 deviation in the direction of the protruded tongue; probably because the 

 tongue is so compact and firm that the muscles on either side can push it 

 straight forward or turn it for some distance toward either side. In hypo- 

 glossal paralysis from cerebral lesions or lesions of the peduncles the paralysis 

 is contralateral. 



IV. THE CEREBELLUM. 



The cerebellum is a large division of the brain, located just beneath the 

 cerebrum and behind the medulla and pons. It is connected with the rest 



FIG. 392. Cerebellum in Section and Fourth Ventricle, with the Neighboring Parts, i, 

 Median groove of fourth ventricle, ending below in the calamus scriptorius, with the longitudinal 

 eminences formed by the fasciculi teretes, one on each side; 2, the same groove, at the place where 

 the white streaks of the auditory nerve emerge from it to cross the floor of the ventricle; 3, in- 

 ferior crus or peduncle of the cerebellum, formed by the restiform body; 4, posterior pyramid; 

 above this is the calamus scriptorius; 5, superior crus of cerebellum, or processus e cerebello ad 

 cerebrum (or ad testes) ; 6,6, fillet to the side of the crura cerebri; 7,7, lateral grooves of the crura 

 cerebri; 8, corpora quadrigemina. (From Sappey, after Hirschfeld and Leveille".) 



of the brain by three peduncles on each side: the superior, the middle, and the 

 inferior peduncle, figure 392. 



The cerebellum is composed of white and gray matter, the latter being 



external, as in the cerebrum, and like it infolded, so that a larger area may be 



contained in a given space. The convolutions of the gray matter, however, 



are arranged after a different pattern, as shown in figure 393. Besides the 



36 



