THE ACOUSTIC COMPLEX OF THE OPOSSUM 409 



cochlear tract, a name rather more descriptive of its course than 

 that of striae acousticae. 



A fourth feature of the model of the cochlear apparatus requir- 

 ing special mention is the incorporation in it of two groups of 

 fibers not concerned in the main conduction path. The first 

 of these is the so-called peduncle of the superior olive (Stiel der 

 kleinen Olive) , which has been repeatedly described, and represents 

 a connection of the auditory path with the nucleus of the sixth 

 nerve. The second is a group of fibers passing from the nucleus 

 lemnisci lateralis towards the median line. This group is present 

 unmistakably in the opossum, has been described especially by 

 von Kolliker, ('96), and mentioned by Held ('93), Cajal ('09) and 

 others, and figured for the cat and the new-born child. In spite 

 of doubt as to their exact origin and distribution it was thought 

 desirable to include them in the model. 



Passing now to the detailed description of the cochlear appara- 

 tus as modelled, it is easy by reconstruction to distinguish in the 

 root of the eighth nerve its two component parts which with the 

 root of the seventh nerve are somewhat diagrammatically rendered 

 in the figures. All three nerve roots lie at about the same level 

 on the wall of the medulla in the opossum, posterior to the pons 

 and the point of entrance of the fifth nerve. The most posterior 

 division represents the N. cochlearis and appears as a robust 

 fiber tract piercing the corpus trapezoideum at an upwardly 

 directed angle, close to its posterior border. As already pointed 

 out, the most anterior portion of the entering nerve passes entirely 

 below the corpus restiforme as it ascends into the cerebellum. 

 The ventral cochlear nucleus, which is first reached by the fibers, 

 is an irregularly oval mass of cells, flattened dorso-ventrally, 

 lying in part below and in part medial to the restiform body and 

 prolonged laterally and posteriorly into the root of the cochlear 

 nerve, in the form of masses of cells between the entering strands. 

 The posterior portion of this lateral extension is cut off from the 

 mass of the nucleus by the restiform body, but is continuous 

 with the main ganglion mass anteriorly. Part of the fibers of the 

 entering nerve pass directly through the ventral nucleus, still 



