THE MEDULLA. 93 



which consists essentially of large cells. One can easily differentiate them 

 in birds and mammals. They are designated in the latter as ventral nucleus 

 and Tuherculum acusticum, and are here larger than the principal nucleus. 

 This last is called in mammals the Nucleus dorsalis. This homology, how- 

 ever, stands on very weak legs, as could be demonstrated if we could go 

 more into the details of the acusticus nuclei of individual vertebrates. 



The terminations of the auditory nerves are connected, not only with 

 the cerebellum, but with numerous other parts of the brain. The whole 

 lateral region of the medulla occupied by the auditory nerves is traversed by 

 fibers and dotted with nuclei, which, either directly or indirectly through 

 collaterals, maintain a connection with the Eighth. For mammals the 

 relations are approximately known. For lower vertebrates the following 

 may be advanced: — 



On the median side there uniformly arise (observed in Selachia, 

 Teleostei, Eeptilia, and Aves) fibers which pass inward into the medulla and 

 connect with a small ganglion there: Oliva superior. In mammals this body 

 has long been known as the Corpus trapezoides. It has also been demon- 

 strated that we have to deal here with a part of the Tractus acustico-tectalis 

 (Fig. 49) : the central connection with the roof of the midbrain. Doubtless 

 there exists also another central connection in the lower vertebrates which 

 does not take its way through the Corpus trapezoides. This is much the 

 larger tract in all animals below the mammals. Note in Fig. 49 thick, easily 

 Aasible fibers, arising from the principal nucleus in a strong tract, passing 

 direct to the median line of the fourth ventricle near the floor, where it 

 approaches the fasciculus longitudinalis posterior and even passes through 

 this to the opposite side. It probably also reaches the tegmentum of the 

 midbrain. Then we would have a Tractus acustico-tectalis ventralis, which 

 passes through the olivary body into the fillet, and also a Tractus acustico- 

 tectalis dorsalis, which would reach the same destination by another route 

 (see Figs. 48 and 49). 



Dorsal to the principal nucleus of the Acusticus lies (in all vertebrates 

 above fishes), imbedded in the most ventral portion of the cerebellum, a 

 large nucleus of multipolar ganglion-cells which, in close connection with 

 the place of origin of the "tonus nerves," send their neuraxons throtigh the 

 territory of the Acusticus back toward the spinal cord. This nucleus is 

 known in mammals as Deiter's nucleus, in general as Nucleus tractus 

 acustico- spinalis. It is possibly a part of the apparatus which is necessary 

 to transmit to the body-musculature the impressions received from the 

 labyrinth (see Fig. 47). It is interesting to note in this connection that 

 in Teleostei a branch from the region leaves the brain, not with the Acusti- 

 cus, but (Stannius) in the nervous system of the lateral line supplied, for 

 the most part, by vagus branches, with which they become associated. The 



