AETEEIAL SYSTEM 



235 



and behind the kidneys, is best seen by dissecting one of the 

 kidneys from the body-wall and turning it inwards. 



The principal branches of the dorsal aorta are as 



follows. 



i. The subclavian arteries are a pair of vessels, 



which arise from the dorsal surface of the 



aorta between the third and fourth pairs of 



efferent branchial vessels, and run outwards 



Fig. 52. — Scyllium eanicula. Transverse section passing through the 

 posterior dorsal fin. (a. m. m.) 

 A, horny fibre. B, fin- ray of the dorsal fin. C, myotomes. "D, neural 

 spine. E, base of neural arch. F, notochord. Gr, calcified portion of centrum. 

 H} haemal arch. 1, spinal cord. !K, lateral vein. Xj, caudal artery. M, caudal 

 vein. 



and backwards in the body-wall and along 

 the hinder border of the pectoral girdle to 

 the pectoral fins, which they supply, 

 ii. The coeliac artery is a large median vessel 

 arising from the ventral surface of the aorta, 

 about half an inch behind the openings of the 

 last pair of efferent branchial vessels. It runs 

 backwards in the mesentery close to the dorsal 



