IX BRAIN 443 



and of Vertebrates in general. The central nervous system 

 is dorsal in position and consists of a brain contained within 

 the cranial cavity, and continuous posteriorly with a spinal 

 cord contained in the neural canal of the vertebral column : 

 it consists of grey and white matter, and its cavity or 

 7ieuroc«k, lined with epithelium, giveis rise to the ventricles 

 of the brain and to the central canal of the spinal 

 cord. 



In correspondence with the form of the body, the spinal 

 cord is relatively much longer than in the frog, and it is not 

 swollen opposite the paired appendages. 



In the brain (Fig. 115) the bulb or medulla oblongata 

 {NH) broadens out anteriorly to form lateral swellings, and 

 its contained fourth ventricle {F. rho) is roofed over by the 

 pia mater. The cerebellum {HB), which is very small in the 

 frog, is here relatively enormous, and its surface is marked 

 by slight grooves : it overlaps the bulb behind and the optic 

 lobes in front, and contains a ventricle communicating 

 with the fourth ventricle. The oval optic lobes (MB.) are 

 hollow, their cavities communicating with the median 

 ventricle or iter (p. 157) ; and ventrally to them are \^e crura 

 cerebri. The diencephalon iZB) is relatively narrower than 

 in the frog. From its thin roof, which covers over the 

 third ventricle, is a delicate tube-like structure (Gp), which 

 extends upwards and forwards and ends in a small knob 

 attached to the roof of the skull : this is the pineal body 

 (p. 159). From the ventral surface of the diencephalon 

 arises the infundibulum, with an oval swelling on either 

 side, to which is attached the pituitary body with a vascular 

 sac on each side of it and a median tubular body on its 

 ventral surface. In front of the infundibulum is the optic 

 chiasma. 



Apart from the large size of the cerebellum, the most 



