THE ACOUSTIC COMPLEX OF THE OPOSSUM 427 



bility of confusing the fiber-group in question with any other 

 structure described for this region, the writer feels obhged to 

 contend that so far as such preparations will support a contention, 

 this represents some form of connection, at least of the corpus 

 trapezoideum and probably of the anterior part of the ventral 

 cochlear nucleus, with the cerebellum. 



The remaining features of the section concern the superior 

 ohve and the nucleus corporis trapezoidei. The two are easily 

 differentiated and the bilobed structure of the former made out. 

 The differentiation of the parts of the nucleus corporis trapezoidei 

 is not very satisfactory. Of the three groups of fibers passing 

 dorso-ventrally through the formatio reticularis, the one nearest 

 the raphe is the sixth nerve, and the middle one of the three can 

 be followed through several sections as the peduncle of the supe- 

 rior olive, connecting it with the nucleus of the sixth. 



Fig. 8. Series A, slide 85, row 1, section 1. This section is 

 through the sensory and motor roots of the fifth nerve, and pre- 

 sents the anterior limits of the vestibular apparatus and the decus- 

 sation of fibers from Bechterew's nuclei, in association with a 

 similar set of fibers from the fifth. As regards the cochlear appa- 

 ratus, the anterior part of the corpus trapezoideum can be seen, 

 and the beginning differentiation of the lateral lemniscus and the 

 nucleus of the lateral lemniscus. Primarily as regards the topog- 

 raphy of the region as a whole, the section serves to indicate the 

 indefiniteness of boundaries between the fifth, the superior ves- 

 tibular and the fastigial nuclei in the wall of the ventricle. The 

 group of fine fibers marked A appearing in cross section are 

 apparently continuations of the fibers of the anterior portion of 

 the medial vestibular nucleus, which have already been referred 

 to. 



Fig. 9. Series A, slide 77, row 1, section 1. This section is 

 taken through the posterior median portion of the inferior colli- 

 culi, just short of the decussation between the two. The fact that 

 in the same section so much of the lateral lemniscus and its dis- 

 tribution, and the nucleus of the colhculus can be shown, illus- 

 trates the abrupt upward sweep of the tract. The capsule of 

 lemniscus fibers on the lateral aspect of the nucleus is also well 



