788 NEUROLOGY 





5. The nucleus of the cochlear nerve consists of: (a) the lateral cochlear nucleus, 

 corresponding to the tuberculum acusticum on the dorso-lateral surface of the 

 inferior peduncle; and (b) the ventral or accessory cochlear nucleus, placed between 

 the two divisions of the nerve, on the ventral aspect of the inferior peduncle. 



The nuclei of the vestibular nerve, (a) The medial (dorsal or chief vestibula.r 

 nucleus), corresponding to the lower part of the area acustica in the rhomboid 

 fossa ; the caudal end of this nucleus is sometimes termed the descending or spinal 

 vestibular nucleus. (6) The lateral or nucleus of Deiters, consisting of large cells 

 and situated in the lateral angle of the rhomboid fossa; the dorso-lateral part of 

 this nucleus is sometimes termed the nucleus of Bechterew. 



The fibers of the vestibular nerve enter the medulla oblongata on the medial 

 side of those of the cochlear, and pass between the inferior peduncle and the spinal 

 tract of the trigeminal. They then divide into ascending and descending fibers. 

 The latter end by arborizing around the cells of the medial nucleus, which is situ- 

 ated in the area acustica of the rhomboid fossa. The ascending fibers either end 

 in the same manner or in the lateral nucleus, which is situated lateral to the area 

 acustica and farther from the ventricular floor. Some of the axons of the cells of 

 the lateral nucleus, and possibly also of the medial nucleus, are continued upward 

 through the inferior peduncle to the roof nuclei of the opposite side of the cere- 

 bellum, to which also other fibers of the vestibular root are prolonged without 

 interruption in the nuclei of the medulla oblongata. A second set of fibers from 

 the medial and lateral nuclei end partly in the tegmentum, while the remainder 

 ascend in the medial longitudinal fasciculus to arborize around the cells of the 

 nuclei of the oculomotor nerve. 



The Cerebellum. The cerebellum constitutes the largest part of the hind- 

 brain. It lies behind the pons and medulla oblongata; between its central portion 

 and these structures is the cavity of the fourth ventricle. It rests on the inferior 

 occipital fossae, while above it is the tentorium cerebelli; a fold of dura mater 

 which separates it from the tentorial surface of the cerebrum. It is somewhat 

 oval in form, but constricted medially and flattened from above, downward, its 

 greatest diameter being from side to side. Its surface is not convoluted like that 

 of the cerebrum, but is traversed by numerous curved furrows or sulci, which 

 vary in depth at different parts, and separate the laminae of which it is composed. ' 

 Its average weight in the male is about 150 gms. In the adult the propor- 

 tion between the cerebellum and cerebrum is about 1 to 8, in the infant about 

 1 to 20. 



Lobes of the Cerebellum. The cerebellum consists of three parts, a median and 

 two lateral, which are continuous with each other, and are substantially the same 

 in structure. The median portion is constricted, and is called the vermis, from its 

 annulated appearance which it owes to the transverse ridges and furrows upon it; 

 the lateral expanded portions are named the hemispheres. On the upper surface 

 of the cerebellum the vermis is elevated above the level of the hemispheres, but 

 on the under surface it is sunk almost out of sight in the bottom of a deep depres- 

 sion between them; this depression is called the vallecula cerebelli, and lodges the 

 posterior part of the medulla oblongata. The part of the vermis on the upper 

 surface of the cerebellum is named the superior vermis; that on the lower surface, 

 the inferior vermis. The hemispheres are separated below and behind by a deep 

 notch, the posterior cerebellar notch, and in front by a broader shallower notch, 

 the anterior cerebellar notch. The anterior notch lies close to the pons and upper 

 part of the medulla, and its superior edge encircles the inferior colliculi and the 

 superior cerebellar peduncle. The posterior notch contains the upper part of the 

 falx cerebelli, a fold of dura mater. 



The cerebellum is characterized by a laminated or foliated appearance; it is 

 marked by deep, somewhat curved fissures, which extend for a considerable dis- 



