THE SKATE. 67 



formed by the union of the efferent branchial trunks is the 

 dorsal aorta (§ 157). 



The efferent branchial arteries unite with one another in the way 

 described at their ventral as well as at their dorsal ends, thus forming 

 complete loops, the spaces enclosed by which correspond to the bran- 

 chial clefts. The two arteries of each complete gill are united with one 

 another by a cross branch at about the middle of their length : it is 

 through this anastomotic branch of the last gill that the ninth efferent 

 artery {e.br. 9) pours its blood into the eighth. From the junction of 

 the third and fourth and of the fifth and sixth arteries, short anastomotic 

 branches go off to the hypobranchial artery {§ 1 39). 



157. The dorsal aorta (Figs. 20 and 21, d.ao), passing 

 along the ventral face of the vertebral column : it gives off, 

 just before being joined by the third pair of efferent branchial 

 trunks, a large vessel from each side, which passes directly 

 outwards to the pectoral fin : this is the brachial or sub- 

 clavian artery (Fig. 20, s.cl, Fig. 21, br.a). The aorta 

 then passes backwards in close contact with the verte- 

 bral column to the posterior extremity of the abdominal 

 cavity, giving off at about the level of the shoulder 

 girdle two large vessels, the coeliac (Fig. 20, ex), and 

 superior mesenteric {s.vi) arteries (§§ 100 and loi), 

 then the arteries to the oviducts (pd) or epididymes, sper- 

 matic arteries (spm) to the testes or ovaries, a single 

 inferior mesenteric artery {i.m), (§ 101), the numer- 

 ous small renal arteries (r) to the kidneys, and vessels to 

 the pelvic fins and the parietes of the body. At the end of 

 the abdominal cavity the dorsal aorta becomes the caudal 

 artery (<;), which passes through the haemal arches of the 

 caudal vertebrae (Fig. 10, hd) to the end of the tail. 



158. The caudal vein (Fig. 17, c), running parallel and ventral 

 to the caudal artery : on leaving the haemal canal it divides into the two 

 renal portal veins {rp), which pass to and ramify in the corre- 

 sponding kidneys {rp") receiving numerous veins (?■/) from the pelvic 

 and lumbar regions. 



F 2 



