408 JOHN H. STOKES 



duction path in most animals is derived to a considerable extent 

 in similar fashion from the tuberculum acousticum, and in the 

 form of the striae acousticae, which form a variable portion of 

 the so-called striae medullares in different mammalian brains, 

 passes dorsally over the restiform body, across the floor of the 

 ventricle towards the median line and downward in the raphe, 

 or by a more direct route downward on the medial side of the 

 tractus spinalis N. vestibularis, to be distributed to the superior 

 olivary nucleus of the same side or to the corpus trapezoideum 

 to undergo decussation to the opposite side. In the human brain 

 it has been shown that the striae medullares have relatively little 

 to do with the auditory conduction path, though in the cat and 

 rabbit they are largely auditory. In the opossum the dorsal con- 

 duction path is a prominent feature, and as in other animals 

 investigated, is apparently largely derived from the dorsal coch- 

 lear nucleus. That this is not the exclusive source, however, is 

 readily seen from the numerous fibers having apparently a dis- 

 tinct origin in the mass of the ventral nucleus, which pass upward 

 along the lateral aspect of the tractus spinalis N. vestibularis, and 

 arching over it, join the dorsal path as it passes downward on the 

 medial aspect of the vestibular tract. The opossum brain does 

 not, however, present any definite group of striae medullares 

 passing across the floor of the ventricle. The entire picture is 

 usurped by the dorsal path, the variation in whose course as 

 regards the corpus restiforme is due to the above described rela- 

 tion of that tract to the cochlear nuclei. The corpus restiforme 

 being external to the cochlear nuclei, the fibers of the dorsal path 

 simply collect on the medial border of the tractus spinalis N. 

 vestibularis and without any deflection towards the median line, 

 pass directly downward through the anterior portion of the medial 

 vestibular nucleus to the superior olivary nucleus. While it should 

 remain with histological study by Golgi methods to determine 

 whether this tract represents the exclusive course of fibers of the 

 dorsal path, it is obviously the principal one in the opossum. 

 Since it is at best no more than a homologueof the striae acousticae 

 it was designated in the models for convenience as the olivo- 



