GENERAL MORPHOLOGY OF THE NERVOUS SYSTEM. 



17 



ventral horns of the gray matter of the cord continue into the 

 myelencephalon and are marked by two grooves which bound 

 laterally the two ridges just mentioned. In the lateral zones 

 there is much greater change from the cord to the brain. The 

 greater size of the myelencephalon is due chiefly to the greater 

 volume of these lateral parts and to their bulging laterally. From 

 the internal surface of the lateral wall there projects into the 

 cavity a ridge constituted chiefly of a thickening of the gray 

 matter. It extends from the caudal end of the myelencephalon 

 to near the cephalic end, stopping abruptly opposite the seventh 

 or faciahs. nerve. This ridge has been known as the lobus vagi 



Fig. 4. — Two views of the brain of the buffalo fish, Carpiodes velijer (Raf.); 

 (i) from above, (2) from the right side. Twice the natural size. From C. Judson 

 Herrick after C. L. Herrick. 



The vagal lobes (L. vg.) are vety large and, with the overhanging cerebellum, 

 completely conceal the facial lobe. In the upper figure the cerebellum appears as 

 a nearly rectangular body in front of the vagal lobes and in front of this is the 

 roof of the mesencephalon. The optic lobes are pushed wide apart by the enormous 

 valvula cerebelli within and the shaded area in the figure represents a membranous 

 portion of the roof connecting the optic lobes. In front of this is the basal ganglion 

 of the forebrain, the membranous roof of which has been cut away. The olfactory 

 bulbs are cut away. In the lower figure the large inferior lobes are seen below the 

 optic lobes and behind the latter the cerebellum is produced ventrally as the superior 

 secondary gustatory nucleus. Immediately behind this and above the VIII nerve 

 is the lobus lineae lateralis. The nerves of the trigemino-facial root complex are 

 marked Vi.d, Vi.v, V2 and VII, the auditory nerve VIII, and the glossopharyngcus 

 and vagus IX and A'. 



