76 



ANATOMY OF THE OENTEAL NEETOUS SYSTEM. 



Besides the changes above noted the nervous system is much greater 

 in cross-section through the medulla than at any point posterior to that. 

 This may be attributed to two circumstances: (1) the appearance of the 



<S>> 



Mg. 37. — Sagittal section of an amphibian brain a little to one side of the 

 median plane. Note the continuity of the Tela chorioidea posterior with the 

 cerebellum. Note, also, the ample folds of the Tela, indicating that its surface 

 is much greater than necessary to cover the fourth ventricle. Med. spin., Spinal 

 cord. Nachh., Medulla oblongata. Hinterhirn, Floor of cerebellum (pons). 



Formatio reticularis, an "association-system" of short fibers, which is to be 

 met at any point between the spinal cord and the base of the Thalamen- 

 cephalon, but which is especially developed here; (3) the presence of nerve- 

 centers. Within the skull there arise within a very short space three very 



Fig. 



38. — Brain of Gadus wglefiints. Those parts which do not belong directly 

 to cranial nerves are shaded. 



1'^ ^ 



large nerves: the Vagus, the Acusticus, and the Trigeminus. Where they 



take their origins — i.e., at the location of the nuclei — the central organ is 



naturally much enlarged. The rich cerebral and cerebellar connections to 



such nerve-centers also add not a little to the volume of the medulla. 



