GENERAL CUTANEOUS SUBDIVISION. 115 



spinalis trigemini. A small part of the fibers of the trigeminus, 

 however, run directly to the cerebellum. The tractus spinalis 

 trigemini is accompanied by an end-nucleus which is directly 

 continuous with the gelatinous substance of the dorsal horn of 

 the cord. This substantia gelatinosa is made up of small and 

 large cells. The neurites of the small cells are either short, ending 

 in the immediate vicinity, or are directed forward or backward 

 within the substantia gelatinosa itself. The neurites of the 

 large cells go as internal arcuate fibers to the opposite ascending 

 lemniscus or to a part of the lemniscus system on the same side. 

 The structure of the substantia gelatinosa of the rabbit is shown 

 in Figure 56. 

 The primitive condition of the general cutaneous centers as 



FIG. 57. A transverse section of the spinal cord of a cyclostome fish, Lampetra 

 Wilder i to show the cells of the dorsal horn (d. h.}. 



seen in lower vertebrates differs considerably from this. In fishes 

 the trigeminus and ophthalmicus profundus fibers may or may 

 not bifurcate on entering the medulla oblongata. When they 

 bifurcate one branch goes to the cerebellum and the other either 

 into the tractus spinalis trigemini or into the deeper part of the 

 tuberculum acusticum. When they do not bifurcate the fibers 

 may take any one of these courses. Further, in selachians, 



