376 MANUAL OF ZOOLOGY SECT, 



of the body cavity, giving off numerous branches, and is 

 continued as the caudal artery (cd. #.), which runs in the 

 canal enclosed by the inferior arches of the caudal vertebrae. 



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

 remarkable 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. 



The venous blood is brought back from the head by a 

 pair of jugular or anterior cardinal sinuses (/. #.), and from the 

 trunk by a pair of posterior cardinal 'sinuses (crd. #.). At the 

 level of the sinus venosus the anterior and posterior 

 cardinals of each side unite to form a short, nearly transverse 

 sinus, \he pre-caval sinus or ductus Cuvieri (pr. cv. v.), which 

 is continued into the lateral extremity of the sinus venosus. 



There are two portal systems of veins, the renal portal 

 and the hepatic portal by which the kidneys and liver, 

 respectively, are supplied with venous blood. The caudal 

 vein (cd. z/.), which brings back the blood frpm the tail, 

 running, below the caudal artery, through the inferior 

 arches of the vertebrae, divides on entering the abdomi- 

 nal cavity into right and left renal portal veins (r.p.v.\ 

 which end in a number of afferent renal veins supplying the 

 kidneys. 



The hepatic portal vein (h. p. v.} is formed by the con- 

 fluence 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 (h.v.) placed 

 close together. 



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

 cephalon (Fig. 205, V.H.), divided into two lateral parts by a 

 very shallow median longitudinal groove. From its antero- 



