CIRCULATORY SYSTEM. 545 
The ventral aorta gives off a pair of posterior innominate arteries, 
which take blood to the three posterior gills, and a pair of anterior 
innominate arteries, which supply the anterior gill and the hyoid half- 
gill on each side. 
The purified blood passes from each half-gill by an efferent branchiah 
artery. To begin with, there are nine of these on each side, but by 
union they are reduced first to four and then to three efferent trunks, 
which combine to form the dorsal aorta. 
From the efferent branchial of the hyoid arch a carotid arises, which: 
divides into internal and external branches supplying the brain: and 
head. The two internal carotids unite, and pass through a small hole: 
‘i ae 
Fic. 287.—-Heart and adjacent vessels of skate.—In part 
after Monro. 
v., Ventricle; ¢.@., conus arteriosus ; #.t., posterior innominate ; 
Ua, ventral aorta ; @.7., anterior innominate ; 7’4., thyroid; 
M., ‘mouth ; a, auricles S.%., sinus venosus 3 S.C, precaval 
sinus or sinus of Cuvier ; "he Sey hepatic. sinus ; j., jugular; dn, 
brachials ; cdi, cardinal ; efg., epigastric. 
on the ventral surface of the skull. Just after the first and second mair 
efferent branches have united, a vertebral is given off, which passes. 
through a hole in the vertebral plate to the spinal cord and brain. 
The dorsal aorta gives off—(1) a subclavian to each pectoral fin ; (2) a. 
coeliac to the stomach, duodenum, and liver; (3) a superior mesen- 
teric to the intestine, pancreas, and spleen; (4) spermatic arteries to 
the reproductive organs; (§) an inferior mesenteric to the rectum ; 
(6) renal arteries to the kidneys; (7) arteries to the pelvic fins. It 
ends in the caudal artery. 
At each end of the bow-shaped sinus venosus there is a precaval 
sinus. This receives venous blood as follows :—(a) from the head by 
35 
