CIRCULATORY SYSTEM. 
557 
buried in the tissues of the gills and head. Many related 
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 
rele 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 
trunks, which unite on each side 
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 
veins, and by hepatics from the liver. 
Fic. 298.—Diagram of 
Teleostean circulation.— 
After Nuhn. ‘ 
A., auricle; V., ventricle; .a.,. 
bulbus arteriosus ; v.@., ventral 
aorta; a.dr., afferent branch- 
ials; ¢.d7., efferent branchials; 
e.¢., cephalic circle; ¢., caro- 
tids; 4.c.v., anterior cardinal’ 
veins; P.C.V., posterior car- 
dinal veins; d.c., ductus 
Cuvieri; d@.a., dorsal aorta;. 
¢.v., caudal vein; ¢.@., caudal 
artery; K., kidney. 
by two vertical precaval 
Each precaval vein is. 
