THE NECTURUS 63 



under a cover slip and examine under a low power to study 

 the large pigment cells. 



Drawing 23. Make a drawing of the dorsal side of the biain X 6 

 showing the cranial nerves. 



The large anterior lobes represent the anterior lobe 

 of the brain. This is a combined rhinencephalon and 

 cerebrum. There is no line of demarcation between them. 

 A prominent pineal body or epiphysis extends forward 

 between the lobes of the cerebrum. This flattens out on 

 the inner side of the skull roof but does not penetrate it. 

 The diencephalon does not show from the dorsal side. The 

 median region or the mesencephalon is smooth and un- 

 marked. The posterior end of this represents the cere- 

 bellum, although there is no external indication of its 

 presence or its limits. The optic lobes are not so evident 

 from the exterior view. A large triangular groove pos- 

 terior to the cerebellum, is the fossa rhomboidalis. The 

 medulla oblongata is posterior to the mesencephalon and 

 contains the fourth ventricle. The medulla passes into the 

 cord with no dividing line. 



CENTRAL NERVE SYSTEM 



Nerves of the Dorsal Side 



The nervus terminalis is so closely associated with the 

 olfactory in Necturus that special methods must be used 

 to isolate it. It is practically internal in this form. 



(1) The large olfactory nerve extends anteriorly from 

 the anterior lobes to the nasal region where it spreads out 

 fan shaped into a number of fibers that supply the nose. 

 Dissect it free so that the branches in the nasal region 

 can be seen. (2) The optic nerve extends out laterally 

 from the diencephalon or 'twixt brain and continues to the 



