THE ACOUSTIC COMPLEX OF THE OPOSSUM 431 



tract of the vestibular is also apparent. These cells are conspicu- 

 ous in the sections owing to the brownish color they take from the 

 mordanting and staining, so that the nucleus is usually easily 

 defined. Under A in all three horizontal sections attention is 

 directed to a prominent nuclear mass in the central grey substance, 

 to which a majority of the fibers of the anterior extension of the 

 nucleus medialis N. vestibularis, apparently lead. The region 

 does not differentiate entirely satisfactorily in these Weigert 

 preparations, and the fibrils are very delicate, which tend to make 

 conclusions about them rather vague. The connection of the 

 band of fibers with the medial vestibular nucleus is the more 

 apparent of the two terminations of the group. The writer has 

 not encountered any description of such a structure as this path 

 or such connection with the central grey substance as it apparently 

 presents, in any account of the vestibular system that he has 

 seen. The nuclear mass in the neighborhood of the point of 

 entrance of the fibers presents a considerable clump of fairly 

 large ganglion cells. More medially the mass presents somewhat 

 the appearance of the substance of the medial vestibular nucleus, 

 the cells in this portion being very much smaller. The relation 

 to the mesencephalic fifth is seen in fig. 10. 



Fig. 12. Series B, slide 82, section 2. This section is taken still 

 more ventral to the two preceding. The spinal tract and Deiter's 

 are again conspicuous and the olivo-cochlear tract is seen in cross 

 section as in the preceding figure. The chief feature of interest 

 is the decussation between fibers from Bechterew's nuclei (marked 

 A) in connection with a decussation of fibers from the fifth 

 (marked B), posterior to it in the main, though in the transverse 

 sections (fig. 8) the two are seen in the field at the same time. In 

 the human brain, according to Sabin, this Bechterew decussation is 

 as closely associated with the brachium conjunctivum as it is 

 with the fifth in the opossum. This section also illustrates very 

 satisfactorily the connection of the corpus ponto-bulbare with the 

 posterior border of the pons. The presence of large numbers of 

 delicate fibrils can only be indicated in the drawing. No ganglion 

 cells can be distinguished in these preparations. 



