4jS THE DOGFISH CHAi'. IX 



dorsal aorta is continued forwards, anteriorly to the first epibranchial 

 artery, as a slender vessel which soon bifurcates and anastomoses with 

 the dorsal carotid. From the ventral ends of the efferent branchial loops 

 small arteries are given off which supply the lower parts of the head, 

 the branchial region, and the heart {for). The sithilavian arteries 

 {s. el) arise from the aorta just before it is joined by the last epi- 

 branchials. 



In the short-hodied frog we have seen (p. 80) that there is only ^ 

 single splanchnic artery, which soon divides into a coeliac and a mesen- 

 teric. In the dogfish there are four splanchnic arteries, arising sepa- 

 rately from the dorsal aorta, viz., a ealiac, supplying the proximal ends 

 of the stomach and intestine, the liver, and pancreas ; an anterior mesen- 

 teric, arising a short distance further back and supplying the intestine, 

 &c. ; a /ieno-gastric, coming off from the aorta close behind the anterior 

 mesenteric and going to the spleen and part of the stomach and pan-, 

 creas ; and a sm?i\\ posterior mesenteric supplying the rectal gland. 



As in all Vertebrates, the arteries branch and branch again 

 in the various parts to which they are distributed, their ulti- 

 mate ramifications opening into a capillary network with 

 which all the tissues except the cartilages and epithelia are 

 permeated. From these systemic capillaries the blood is 

 collected into larger and larger efferent, thin-walled, trunks or 

 WW, parts of many of which are greatly dilated to form sinuses. 



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

 jugular veins (Figs. no,/, v. and iisyVi'^'. v) : each of these 

 enters a large precaval sinus {pr. cv. v, dct. c) which passes 

 vertically downwards and enters the sinus venosus. The blood 

 from the tail is returned by a caudal vein (cd. v, caud. v) 

 lying immediately beneath the caudal artery in the haemal 

 canal ; this vessel enters the ccelome and then divides into 

 right and left branches, the renal portal veins {r. p. v, 

 r. port, v), which pass to the kidneys and join with the 

 capillaries of these organs, the impure blood brought from 

 the tail mingling with the pure blood of the renal arteries 

 (Fig. 110, r.a). From the kidneys the blood is returned 



