ARTERIAL SYSTEM 415 



entirely into the cranial cavity, and supplies the brain with blood, 

 while the external carotid goes to the external parts of the head 

 (face, tongue, and muscles of mastication). 



In Fishes a series of nutrient branchial vessels arise in connec- 

 tion with a hypobranchial artery formed by the union of vessels 

 given off from the ventral ends of the afferent branchial arteries 

 (Figs. 320, 321, and cf. note on p. 405). 



The origin of the subclavian artery, 1 which supplies the 

 anterior extremity, is very inconstant, being sometimes symme- 

 trical, sometimes asymmetrical. It arises either in connection 

 with the posterior afferent branchial vessels, or from the roots or 

 main trunk of the aorta. Extending outwards towards the free 





FIG. 320. DIAGRAM OF THE BRANCHIAL ARTERIAL SYSTEM OF Miif-telus 

 antarcticus. Left lateral view. (From Bridge, after T. J. Parker.) 



The ventral aorta and afferent branchial vessels are in solid black ; the afferent 

 arteries and their branches have double contours. The branchial clefts have 

 fringed borders to indicate their hemibranchs, and the arches are in simple 

 outline. 



a.c.a, anterior (ventral) carotid; a.d.a, anterior dorsal aorta; af.b.a, afferent 

 branchial; br.a, brachial ; c.m.a, coeliaco-mesenteric ; d. a, dorsal aorta ; E, 

 eye; ep.a, epibranchial ; H, heart; h.b.a, h3 T pobranchial ; hy.a, afferent 

 pseudobranchial or hyoidean ; md.a, mandibular ; op.a, ophthalmic ; p.c.a, 

 posterior (dorsal) carotid ; sb.a, subclavian ; sp, spiracle ; v.a, ventral aorta ; 

 1 5, the hyobranchial and four succeeding branchial clefts. 



extremity, the subclavian passes into the brachial artery, which in 

 higher forms divides into an ulnar and a radial branch, and these 

 again subdivide to form the arteries of the manus. The 

 condition seen in lower forms and in certain embryonic stages of 

 higher types shows that these vessels arise from networks, which 

 occur more particularly along the larger nerve-trunks. Each 

 main vessel is therefore merely a more strongly developed portion 

 of a connected system of canals which, especially in the 

 axillary region, is seen to be formed originally from segmental 

 vessels connected by longitudinal anastomoses. 



1 In the Amphibia the great cutaneous arter}', arising from the subclavian, 

 extends backwards, anastomoses with the epigastric artery, and gives off 

 numerous branches to the skin. 



