146 ZOOLOGY SECT. 



these a number of small arteries, the parietal, supplying the 

 wall of the body, are given off throughout the length of the 

 aorta. 



The veins are very thin-walled, and the larger trunks are re- 

 markable for their dilated character, from which they have 

 obtained the name of sinuses, though they are true vessels and 

 not sinuses in the sense in which the word is used in dealing 

 with the Invertebrates (cf. p. 87). 



The venous blood is brought back from the head by a pair of 

 jugular or anterior cardinal sinuses (Fig. 774, /?6#. v.), and from the 

 trunk by a pair of posterior cardinal sinuses. At the level of the 

 sinus venosus the anterior and posterior cardinals of each side unite 

 to form a short, nearly transverse sinus, the preca/vqj, sinus or ductus 

 Cnvieri (Fig. 774,dc.c.), which is continued into the lateral extremity 

 of the sinus venosus. Into the ductus Cuvieri, about its middle, opens 

 an inferior jugular sinus (inf. jug. v.) which brings back the blood 

 from the floor of the mouth and about the branchial region of the 

 ventral surface. The two posterior cardinal sinuses extend back- 

 wards throughout the length of the body cavity ; in front they are 

 enormously dilated, behind they lie between the kidneys. Ante- 

 riorly each receives the corresponding subclavian vein, bringing 

 the blood from the pectoral fin and adjacent parts of the body- 

 wall. The lateral vein (Lv.\ instead of joining with the sub- 

 clavian (p. 87), opens separately into the precaval. The genital 

 sinus discharges into the posterior cardinal sinus. 



There are two portal systems of veins, the renal portal and the he- 

 patic portal (hep. port. 1'.), by which the kidneys and liver, respectively, 

 are supplied with venous blood. The caudal vein, which brings back 

 the blood from the tail, running, along with the caudal artery, 

 through the inferior arches of the vertebra, divides on entering 

 the abdominal cavity into right and left renal portal veins, which 

 end in a number of afferent renal veins supplying the kidneys. 



The hepatic portal vein (h.port. v.} is formed by the confluence 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. In Chiloscyllium a large branch connects the genital 

 sinus with the intestinal tributaries of the hepatic portal system. 

 The blood from the liver enters the sinus venosus by two hepatic 

 sinuses placed close together. 



Nervous System.- -The fore-brain consists of a rounded, 

 smooth prosencephalon (Fig. 775, 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.oL), closely 

 applied to the posterior surface of the corresponding olfactory 

 capsule. The diencephalon (ZH) is comparatively small ; its roof 

 is very thin, while the floor is composed of two thickish masses 



