PHYLUM CHORDATA 



351 



In the lizard the heart and the circulation are somewhat 

 more complicated than in the dogfish. There is a sinus 

 venosus as before. The auricle is completely divided into 

 two chambers, right and left, by a partition. Into the right 

 auricle the sinus venosus drives the venous blood from the 

 great veins ; into the left open the pulmonary veins, bring- 

 ing the oxygenated blood from the lungs. Both the auricles 

 open into the ventricle, the cavity of which is partly divided 

 by a septum. From the ventricle are given off the main 

 arteries (systemic arteries) which branch throughout all parts 



d go 



*> bra 



a bra 



au &V 



tic 218 — Diagram illustrating the course of the circulation in a fish. Vessels 

 containing aerated blood, red; those containing non-aerated blood, blue; lym- 

 phatics, black. B, capillaries of the body generally; E, of the enteric canal; 

 G, of the gills; K, of the kidneys; L, of the liver; T, of the tail. a. br. a, 

 afferent branchial arteries; an, auricle; c. a, conus arteriosus; d. no, dorsal 

 aorta; e. br. a, afferent branchial arteries; h. p v, hepatic portal vein; h. v, 

 hepatic vein; lc t lacteals; ly, lymphatics; pr. cv. v, pre-caval veins; r. p. v. 

 renal portal veins; s. v, sinus venosus; v, ventricle; zi. ao t ventral aorta. The 

 arrows show the direction of the current. 



of the body, and the pulmonary arteries, which pass direct 

 to the lungs. By various arrangements of the parts which 

 need not be described at present, the venous blood from 

 the right auricle is mainly guided into the pulmonary arte- 

 ries, and passes to the lungs to obtain oxygen and part with 

 its carbon dioxide ; while the arterial blood is mainly guided 



