380 MANUAL OF ZOOLOGY SECT. 



ence of veins derived from the intestine, stomach, pancreas, 

 and spleen, and runs forwards to enter the liver a little to 

 the right of the middle line. The blood from the liver 

 enters the sinus venosus by two hepatic sinuses (Ji. v) placed 

 close together. 



The fore-brain consists of a rounded, smooth prosen- 

 cephalon (Fig. 219, V. H), divided into two lateral parts by 

 a very shallow median longitudinal groove. From its antero- 

 lateral region each half gives off a thick cord, which dilates 

 into a large mass of nerve matter, the olfactory lobe (L. <?/), 

 closely applied to the posterior surface of the correspond- 

 ing olfactory capsule. The diencephalon (Zff) is com- 

 paratively small ; its roof is very thin, while the floor is 

 composed of two thickish masses, the optic thalami. At- 

 tached to the roof is a slender tube, the epiphysis cerebri or 

 pineal body ( Gp) , which runs forwards and terminates in a 

 slightly dilated extremity fixed to the membranous part of 

 the roof of the skull. Projecting downwards from its floor 

 are two rounded bodies, the lobi inferiores, which are dilated 

 portions of the infundibulum ; and attached to this, behind, 

 is a thin- walled sac , the pituitary body or hypophysis cerebri 

 having a pair of thin-walled vascular lateral diverticula, the 

 sacci vasculosi, and having on its ventral surface a median 

 tubular body attached at its posterior end to the floor of the 

 skull. In front of the infundibulum, and also on the lower 

 surface of the diencephalon, is the optic chiasma, formed by 

 the decussation of the fibres of the two optic nerves. The 

 mid-brain (MU) consists of a pair of oval optic lobes 

 dorsally, and ventrally of a band of longitudinal nerve-fibres 

 corresponding to the crura cerebri of the higher vertebrate 

 brain. The cerebellum {HH) is elongated in the antero- 

 posterior direction, its anterior portion overlapping the 

 optic lobes, and its posterior the medulla oblongata. Its 



