THE ACOUSTIC COMPLEX OF THE OPOSSUM 405 



in two nuclei of reception, the dorsal and ventral, the dorsai 

 cochlear nucleus being identical with the so-called tuberculum 

 acousticum. From these two nuclei of reception the auditory 

 path is generally represented as continuing in part by way of the 

 corpus trapezoideum on the ventral surface of the brain stem and 

 in part by way of the striae acousticae on the dorsal, to the nuclear 

 masses associated with the corpus trapezoideum, and to the lateral 

 leminiscus and its associated ganglion mass. The distribution 

 of these centrally directed fibers among the fiber tracts in question 

 and their terminations in the superior olive and the nuclei of the 

 corpus trapezoideum and the lateral lemniscus, are still among the 

 unsettled questions in the finer structure of the central acoustic 

 path. The proportion of acoustic fibers in the striae has also been 

 shown to vary in different mammalian brains. It is now well 

 recognized, however, and the point is of significance in the study 

 of the models, that most of the fibers from the cochlear nuclei 

 of one side of the brain cross the median line and are either inter- 

 rupted in the superior olive or in the nucleus corporis trapezoidei, 

 or are continued into the lateral lemniscus, of the opposite side. 

 The corpus trapezoideum is therefore essentially a decussating 

 path connecting the cochlear apparatus and more especially the 

 cochlear nuclei of one side with the nuclear masses and the lateral 

 lemniscus of the other. The value of keeping this relation in 

 mind in studying the model is apparent. In the elongated grey 

 mass of the nucleus of the lateral lemniscus a portion of the fibers 

 which cross by way of the corpus trapezoideum or originate from 

 cells in the nuclear masses of that tract, are interrupted. The 

 fibers of the lateral lemniscus terminate in considerable numbers 

 in the nuclear mass of the inferior colliculus. A portion of the 

 fibers of the lateral lemniscus are prolonged beyond the inferior 

 colliculus, and joined presumably by fibers from cells within the 

 nucleus of the inferior colliculus, proceed by way of the brachium 

 colliculi inferioris to the corpus geniculatum mediale, whose nucleus 

 constitutes the last of the sharply defined stations in the path. 

 From this point the remnants of the lateral lemniscus, and other 

 groups of fibers associated with the eighth apparatus, are pro- 

 longed cerebral ward. 



