THE OBLONGATA AND THE NUCLEI OF THE CRANIAL NEEVES. 77 



One usually has little conception of the great size of those parts of the 

 central nervous system which are in connection with the cranial nerves 

 among lower vertebrates. In the brain of the fish Gadus wglefinus (Pig. 38) 

 the nerve-roots alone aggregate a much greater mass than that part of the 

 brain not in relation to the nerves in question. 



Sections through the medulla of fishes show that this is, for the most 

 part, simply the origin of the great cranial nerves. All other systems of 

 fibers are, compared with these, quite in the background. There exist also 

 within the medulla several special centers which are in relation with the 

 cerebellum and with the acusticus. 



Finally, it is to be mentioned that this part of the nervous system is 



Fig. 39. — Dorsal view of the Oblongata and cerebellum of the sturgeon: 

 Acipenser ruthenus. The Tela is dissected off and lies at the left. Note the 

 large nuclei of the N. trigeminus, the N. acusticus, and the N. vagus. (After 

 Goronowitsch.) 



traversed by those tracts which pass to the spinal cord from the regions 

 anterior to it, as well as fibers from the same source destined for the medulla 

 itself. 



These notable changes which appear at the cephalic end of the spinal 

 cord are still more apparent on cross-sections than in the outer form. 



It may be best to choose as the first object for observation the medulla 

 of the amphibian larva, because of its simple structure and its gradual 

 differentiation from the cord (see Fig. 40). 



