THE MAMMALIAN NERVOUS SYSTEM 73 



larly the papers of Hardesty ( J 08a) and ('15), Prentiss ('13), 

 Shambaugh ('07) and ('08), and Van der Stricht ('18). 



81. Gross preparation of the cochlear nerve and its connec- 

 tions. In the gross specimens locate the inferior peduncle of 

 the cerebellum (corpm restiforme), which connects the dorso- 

 lateral wall of the medulla oblongata with the cerebellum. 

 This is crossed immediately behind the cerebellum by the dor- 

 sal cochlear root and nucleus of the VIII nerve (called the tuber- 

 culum acusticum) . Find this structure in both the human and 

 the sheep's brain. Immediately ventro-laterally of the dorsal 

 cochlear nucleus at the point where the cochlear root of the VIII 

 nerve enters the brain is found the ventral cochlear nucleus. 



Root-fibers of the cochlear nerve terminate in both the dorsal 

 and the ventral cochlear nuclei. Fibers of the central acoustic 

 path leave these nuclei by two chief tracts. From the ventral 

 nucleus they enter the trapezoid body (corpus trapezoideum) , 

 which can be seen in the sheep's brain as a wide transverse band 

 on the ventral surface immediately below the pons. In the 

 human brain these fibers are covered by the fibers of the pons 

 and cannot be seen without dissection of the pons. From the 

 dorsal cochlear nucleus the secondary acoustic path passes 

 medialward along the surface of the floor of the fourth ven- 

 tricle, thus forming the striae medullares acusticse, which are 

 Very conspicuous in the human medulla oblongata, but less so 

 in the sheep. The further course of the ventral acoustic tract 

 can readily be dissected in the sheep's brain. Having crossed 

 the midplane in the trapezoid body, they enter or pass close to 

 the superior olive and then turn forward to form the chief com- 

 ponent of the lateral lemniscus (lateral fillet) , which terminates 

 in the inferior colliculus and medial geniculate body. 



On the left half of the sheep's brain, which has been divided 

 in the median plane (see Figs. 7, 8, 11, 12) locate the root of the 

 cochlear nerve and its nuclei. The connection of the ventral 

 cochlear nucleus with the trapezoid body farther ventrally can 

 readily be demonstrated. Now observe the relations of the 

 pons and the brachium pontis and of the brachium conjunc- 

 tivum (superior cerebellar peduncle). 



The fibers of the latter will be seen to be directed forward, 

 medialward, and ventralward. On the lateral surface of the 



