582 Dynamic Tlieory. 



bend down between the cerebellum and the cerebrum, sinking the optic 

 lobes to a plane below the other ganglia. (Fig. 293.) The hemispheres 

 are smooth, but have ventricles, and in them are formed the corpora 

 striata and choroid plexus. Anterior to the optic lobes are the thalami 

 optici, formed upon the crura cerebri. The brain of crocodile differs 

 only in minor matters from that of the turtle. The cerebral lobes are 

 relatively larger. The cerebellum is gashed by a transverse fissure, or 

 fold. The optic lobes have each a ventricle, into which a convex body 

 projects, something after the manner of the corpus striatum into the 

 cerebral ventricle. The olfactory lobes at first near the cerebrum, move 

 off with the growth of the animal, and remain connected by crura. 



FIG. 298. FIG. 296. FIG. 297. 



FIG. 296. Side view of Brain of Lizzard (Psammosaurus Bengalensis). 

 FIG. 296. Top view of same. 



Cb. Cerebellum. 



mo. Medulla oblongata. 



ii. Optic nerve (second nerve). 



iv. Pathetic nerve ( fourth nerve ). 



vi. Abducens (sixth nerve). (Huxley.) 



FIG. 297. Side mew of Brain of Turkey. 



FIG. 298. Top view of same. 

 O(/.-01factory lobes ( in all ). 

 H. Cei-ebral hemispheres. 

 pn. Pineal gland. 

 nib. Optic lobes. 

 py. Pituitary gland. 



There is, in reptiles, an anterior commissure, usually small. There is 

 no pons varolii. 



The spinal cord of birds, like that of other vertebrates, expands in 

 volume opposite the parts related to the limbs wings and legs. The 

 part of it developed in the tail extremity of the embryo, shrinks up 

 into a mere filamentar}'" trace of its first condition, and does not fill up 

 the neural canal. It becomes larger in the sacral region as the legs 

 grow. The spinal cord becomes more slender in the dorsal region, and 

 expands again near the base of the neck at the shoulders, where the 

 nerves of the fore limbs join it. There is a ventral and a dorsal side to 

 the spinal cord, and a canal through the middle. The ventral side is 

 nearly split in two by a longitudinal fissure, which cleaves it almost to 

 the canal. There is also a dorsal fissure not so well marked or deep as 



