AVKS. 253 



stalked pineal gland is connected with its thin roof, and a 

 pituitary body with the infundibulum formed by its floor. This 

 part of the fore-brain is overlapped by the large smooth cerebral 

 hemispheres. These are ovoid bodies closely applied to each 

 other in the middle line, broadest behind and bluntly pointed in 

 front. Each contains a large lateral ventricle, communicating 

 with the third ventricle by a foramen of Monro, and having its 

 floor raised into a considerable elevation, the coitus striatum. 

 The two corpora striata are connected by the anterior commissure 

 running in the lamina terminalis. A small pointed olfactory lobe 

 is connected with the anterior end of each hemisphere, close to 

 the middle line on the ventral surface, and it contains a small 

 olfactory ventricle, continuous with the lateral ventricle. 



(b) Mid-brain. The optic lobes are very large. They are widely 

 separated from one another, and situated laterally, but remain 

 united by a dorsal optic commissure. Each contains a good-sized 

 optic ventricle, opening into the Sylvian aqueduct, which connects 

 the third and fourth ventricles, and possesses a thick floor formed 

 by the crura cerebri. 



(c) Hind-brain. The thickened cylindrical bulb (medulla ob- 

 longata) possesses shallow dorsal and ventral fissures, and the roof 

 of the fourth ventricle is extremely thin. The cerebellum is a large 

 rounded projection, flattened laterally, which overlaps the mid- 

 brain and medulla. It is marked by deep transverse furrows, 

 and on each side presents a small rounded elevation, the flocculus. 

 The cerebellum is united with the bulb by a large cylindrical 

 peduncle on each side. 



The spinal cord is continuous in front with the bulb, a sharp 

 ventral flexure marking their union, and tapers gradually back ta 

 the caudal region, exhibiting, however, considerable brachial and 

 lumbar enlargements where the limb-nerves come off. Dorsal and 

 ventral fissures are present, and a central canal, which in the lumbar 

 enlargement expands into a sinus rhomboidalis, the lozenge-shaped 

 roof of which is covered by membrane only. 



(2) Cranio-Spinal Nerves. There are twelve pairs of cranial 

 nerves, the first ten of which correspond in origin and distribution 

 to those of the frog (p. 211). The optic chiasma is very large, 

 and the optic tracts very wide. The (V.) trigeminal nerve arises 

 by two roots, upon the larger of which is the Gasserian ganglion.. 

 Owing to the elongation of the neck, a very long course is taken- 



