10 Journal of Comparative Neurology. 



the pre- and the post-auditory portions of this system the old 

 terms lobiis ttigemini and lobiis vagi are retained, the fact being 

 recognized, of course, that the nerve root from the former be- 

 longs rather (on the present nomenclature) to the Vllth than 

 to the Vth nerve. The ** lobus trigemini" of Elasmobranchs 

 and sturgeons will be referred to later. 



Even in its highest development in Amphibia the fasciai- 

 his communis is much simpler than in Ganoids and appears 

 simply as a highway in which fibers of a constant and peculiar 

 appearance turn caudad from the VII, IX and Xth nerves ; and 

 the cells of the adjacent cinerea sending processes into the tract 

 must be considered with it as the end nidus. The so-called 

 lobiis vagi of Ganoids includes nerve cells and thus must be 

 more than the fasciculus communis of Amphibia. This tract in 

 Aniia resembles closely that in Acipenscr and the description of 

 Goronowitsch applies to Amia as well. The tract first appears 

 near the caudal end of the rhetatela, just beneath the endyma. 

 It increases rapidly in size and soon produces a marked swelling 

 in the wall of the oblongata, occupying the most dorsal region, 

 from which it is soon displaced by the development of the 

 acustiaim (dorso-lateral tracts) (Figs. 15-17). From it arise 

 by far the greater part of the sensory fibers of the Xth and 

 IXth nerves and a large root of the Vllth with the exit of 

 which it disappears. In structure it consists of fine fibers with 

 areas of ground substance and interspersed small cells, which 

 also form a layer just beneath the endyma. The general re- 

 semblance between this structure in Ganoids and in Elasmo- 

 branchs is quite close. 



The Aciistiami. The most dorsal portion of the oblongata 

 in Amia is occupied by the "dorso-lateral " tracts, which con- 

 stitute the centre for the acustic and nerves of the lateral line 

 system, and is here spoken of as the acusticum. It has certain con- 

 stant connections with the rest of the brain and is capped by a 

 caudal extension of the molecular layer of the cerebellum 

 ( cerebellar crest ) as already stated. This intimate association 

 of cerebellar structure with this portion of the metencephal is 

 very striking and suggestive. Roughly speaking, in mammals 



