156 ZOOLOGY 



SECT. 



given off from the same efferent vessel supplies the pseudobranch, 

 and the blood from the latter is taken up by ventral carotid (v. c.). 

 Both carotids run forwards to supply the head. 



The dorsal aorta (Fig. 819, d. ao.) runs backwards throughout 

 the length of the body-cavity, giving off numerous branches, and 

 is continued as the caudal artery, which runs in the canal enclosed 

 by the inferior arches of the caudal vertebrae. The first pair of 

 branches are the subclavians (s. cL), for the supply of the pectoral 

 fins ; these are given off between the third and fourth pairs of 

 efferent arteries. The next large branch is the unpaired cceliac 

 (Fig. 817, cceL) : this runs in the mesentery and divides into 

 branches for the supply of the stomach and liver, the first part of 

 the intestine, and the pancreas. iKThe anterior mesenteric artery, 

 also median, supplies the rest of the intestine and gives off 

 branches to the reproductive organs. The lienogastric supplies 

 part of the stomach, the spleen, and part of the pancreas. The 

 posterior mesenteric is a small vessel mainly supplying the rectal 

 gland. Small renal arteries carry a small quantity of arterial 

 blood to the kidneys, and a pair of iliac arteries, likewise of small 

 size, supply the pelvic fins. In addition to 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. 93). 



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

 jugular or anterior cardinal sinuses (Fig. 820, jug. 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 precaval sinus or ductus 

 Cuvieri (Fig.820,dct.c.), which is continued in to the lateral extremity 

 of thesinus 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 siibdavian vein, bringing 

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

 wall. The lateral vein (/.'.), instead of joining with the sub- 

 clavian (p. 94), 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 

 hepatic portal (hep. port, r.), by which the kidneys and liver, 

 respectively, are supplied with venous blood. The caudal vein, 



