CIRCULATORY SYSTEM. 



557 



buried in the tissues of the gills and head, 

 forms are common on fishes. 



The swim-bladder lies along the 

 dorsal wall of the abdomen ; the 

 duct which originally connected it 

 with the gut has been closed. The 

 dorsal wall of the bladder is so 

 thin that the kidneys and vertebrae 

 are seen through it; the ventral 

 wall is thick, and bears anteriorly 

 a large vascular network or 

 rete mirabile, which receives 

 blood from the mesenteric artery 

 and returns blood to the portal 

 vein. 



Circulatory system. The heart 

 lies within a pericardial chamber, 

 separated by a partition from 

 the abdominal cavity. The blood 

 from the body and liver enters the 

 heart by the sinus venosus, passes 

 into the thin-walled auricle, and 

 thence to the muscular ventricle. 

 From the ventricle it is driven up 

 the ventral aorta, the base of which 

 forms a white non - contractile 

 bulbus arteriosus. 



The ventral aorta gives off, on 

 each side, four afferent branchial 

 vessels to the gills. Thence the 

 blood is collected by four efferent 



Many related 



[G. 298. Diagram of 

 Teleostean circulation. 

 After Nuhn. 



trunks, which unite on each side A., auricle; r., ventricle; 



in an epibranchial artery. The 



two epibranchials are united pos- 

 teriorly to form the dorsal aorta, 



while anteriorly they give off the 



carotids, which are united by a 



transverse vessel closing the 



" cephalic circle." 



Blood enters the sinus venosus by two vertical precaval 



veins, and by hepatics from the liver. Each precaval vein is 



bulbus arteriosus ; v.a., ventral 

 aorta; a.br.^ afferent branch- 

 ials ; e.br., efferent branchials; 

 c.c., cephalic circle; e., caro- 

 tids; A.c.v., anterior cardinal 

 veins; P.C.V., posterior car- 

 dinal veins ; d.c., ductus 

 Cuvieri ; d.a., dorsal aorta; 

 c.v., caudal vein ; c.a., caudal 

 artery; K., kidney. 



