CIRCULATION 



389 



portal, which, instead of joining with larger and larger veins, 

 and so returning its blood directly to the heart, breaks up, 

 after the manner of an artery, in the kidney or liver, the 

 blood finding its way into the ordinary venous channels 

 after having traversed the capillaries of the gland in question. 

 Thus an ordinary artery arises from the heart or from an 



d tio 



a. bra. 



FIG. 1O4A. Diagram illustrating the course of the circulation in the 

 Dogfish. 



Vessels containing oxygenated blood, red ; non-oxygenated, blue. 

 B, capillaries of the body generally ; , of the enteric canal ; G, ot 

 the gills ; A", of the kidneys ; Z, of the liver ; T, of the tail. 



a, br. a, afferent branchial arteries , au, auricle ; c. a, conus arteri- 

 osus ; d. ao, dorsal aorta ; e. br. a, efferent branchial arteries ; h. p. v, 

 hepatic portal vein ; h. v, hepatic vein ; Ic, lacteals ; ly, lymphatics ; 

 pr. cv. 57, precaval vein ; r. p. v, renal portal vein ; s. v, sinus venosus ; 

 v, ventricle ; v . ao, ventral aorta. 



The arrows show the direction of the current. 



(From Parker and Haswell's Zoology.} 



artery of higher order and ends in capillaries ; an ordinary 

 vein arises from a capillary network and ends in a vein of 

 higher order or in the heart. But the hepatic and renal 

 portal veins end in capillaries after the manner of arteries, 

 and the efferent branchial arteries begin in capillaries after 

 the manner of veins. 



