CIRCULATORY SYSTEM. 495 



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 branchial 

 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 



Fig. 210. — Heart and adjacent vessels of skate. — In part 

 after Monro. 



v., Ventricle; c.a., conus arteriosus; fi.i., posterior innominate; 

 ■v.a., ventral aorta; a.i., anterior innominate; Tk., thyroid; 

 ?«., mouth; a., auricle ; s.v., sinus venosus ; s.c, precaval 

 sinus or sinus of Cuvier ; h.s., hepatic sinus ; /., jugular ; br., 

 brachials ; cd., cardinal ; ej>g., epigastric. 



head. The two internal carotids unite, and pass through a small hole 

 on the ventral surface of the skull. Just after the first and second main 

 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. cceliac to the stomach, duodenum, and liver; (3) a superior mesen- 

 teric to the intestine, pancreas, and spleen ; (4) spermatic arteries to the 

 reproductive organs ; (5) 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 



