CIRCULATION AND RESPIRATION 



129 



The Blood Vascular System of the Frog. — The arterial system 

 is made up of the arterial trunks leaving the heart and their 

 subdivisions, which go to all parts of the body (Fig. 81). The 

 carotid arteries supply the head. The remainder of the body 

 except the lungs and some parts of the skin are supplied by the 

 aortic arches and the dorsal aorta. The pulmocutaneous arteries 

 lead to the lungs and certain regions of the skin. The arched 

 form of these arterial trunks is a survival of a fish type of bran- 

 chial circulation that is present in the frog tadpole. 



In a fish such as the dogfish shark, a common marine form, 

 the sinus venosus receives all the venous trunks of the body and 



Fiu. 80. — The circulatory system of the dogfish, a, atrium or auricle; a.b.a., 

 afferent branchial arteries; a.c, anterior cardinal vein; b.c, branchial clefts; c.a., 

 carotid artery; c.c.v., common cardial vein; cl.a., caudal artery; cl.v., caudal 

 vein; co.a., coeliac artery; d.a., dorsal aorta; e.b.a., efferent branchial arteries; 

 h.p.v., hepatic portal vein; h.v., hepatic vein; il.a., iliac artery; il.v., iliac vein; k, 

 kidney; I, liver; l.v., lateral vein; m.a., mesenteric artery; p, pancreas; p.c, post- 

 cardinal vein; r.a., renal artery; r.p.v., renal portal vein; r.v., renal veins; s, stom- 

 ach; su.a., subclavian artery; su.v., subclavian vein; s.v., sinus venosus; v. 

 ventricle; v.a., ventral aorta. (Modified from Parker and Haswell.) 



pours its blood into a single atrium (Fig. 80). From the atrium 

 the blood passes into a single ventricle. Thus all of the blood in 

 the dogfish heart is venous blood. Leading forward from the 

 ventricle is a short truncus arteriosus which divides right and 

 left into afferent branchial arteries leading to the gills. After 

 passing through the wide capillaries of the gills, during which the 

 blood absorbs oxygen from water passing over the gills and gives 

 off carbon dioxide to the water, the oxygenated blood is collected 

 dorsally by efferent branchial arteries which unite to form a 

 dorsal aorta that proceeds posteriorly to the tip of the tail. The 

 carotid arteries are given off from anterior efferent arteries to the 

 head. The arrangement of the branchial vessels is such that 

 all of the blood leaving the heart passes through the gills. The 



