THE VASCULAR SYSTEM 



325 



paired lateral branches, the afferent branchial arteries. These 

 pass along the cartilaginous gill-arches and supply the gills, 

 dividing into very fine branches for the purpose. Thus far 



FIG. 90. Diagram of primitive vertebrate circulation, based on the 

 condition found in selachians. 



s, sinus venosus; t, atrium; v, ventricle; x, conus arteriosus; br, branchial arteries; 

 ad, carotid artery; aoa, aortic arch; aod, dorsal aorta; ce, cceliac axis, consisting of 

 (m) mesenteric, and hepatic and splenic (unmarked) branches; cau, caudal arteries 

 and veins; il, iliac arteries and veins; sb, subclavian arteries and veins; ra, renaies 

 advehentes; rr, renaies revehentes; /, lateral vein; cp, posterior cardinal vein; ca, an- 

 terior cardinal vein; p, hepatic portal vein; h, hepatic vein. 



the blood is impure, in the state in which it was received from 

 the body, but at this point there intervenes a system of capil- 



