70 LABORATORY OUTLINE OF NEUROLOGY 



wall of the medulla oblongata with the cerebellum. This is 

 crossed immediately behind the cerebellum by the dorsal cochlear 

 root and nucleus of the VIII nerve (called the tuberculum acusti- 

 cum). Find this structure in both the human and the sheep's 

 brain. Immediately 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 ventricle, 

 thus forming the stria? medullares acustica?, which are very con- 

 spicuous 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 component 

 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 conjunctivum 

 (superior cerebellar peduncle). 



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

 medialward, and ventralward. On the lateral surface of the 

 brain (see Fig. 12, lem.l.) immediately in front of the pons and 

 more ventrally and superficially than the fibers of the brachium 

 conjunctivum are fibers running from the border of the pons 

 obliquely forward and dorsalward, thus crossing at a right angle 

 the deeper fibers of the brachium conjunctivum. These super- 



