434 TEXTBOOK OF ZOOLOGY 



main chambers are the single, more dorsal auricle, and the ventral, 

 muscular ventricle. Leading into the auricle is the sinus venosus, 

 which receives blood from the veins of the body. A bulblike en- 

 largement at the base of the ventral aorta, where it leaves the ven- 

 tricle, is the conus arteriosus. The ventral aorta leads anteriorly 

 from the conus and gives off three pairs of afferent branchial arteries 

 which branch to the five pairs of gills. The blood spreads from these 

 by capillaries through the gill lamellae for oxygenation. The pre- 

 trematic and postreniatic branches of the efferent branchial arteries 

 which form four efferent branchials leave the gills and join the dorsal 

 aorta, which is formed by them in the dorsal midline. The hyoidean 

 extends from the ventral portion of the first pretrematic to the 

 spiracle where it spreads in capillaries. The ventral carotid leads for- 

 ward from the spiracle to the internal carotid. Extending anteriorly 

 from the dorsal part of each first efferent branchial is a common 

 carotid which supplies arterial blood to the head and brain. The 

 dorsal aorta extends posteriorly from the junction of the efferent 

 brachial arteries, soon giving off the subclavian arteries to the pectoral 

 fins; coeliac to stomach, liver, and pancreas; gastrosplenic to stomach 

 and spleen; superior mesenteric to the valvular intestine to be- 

 come the posterior mesenteric artery there; renal arteries to the 

 kidneys; the inferior mesenteric to the rectal gland and large intes- 

 tine; and the iliac to the pelvic fins and cloaca. The subclavian 

 artery leaves the aorta more anteriorly, coming off ahead of the pos- 

 terior efferent branchial ; the coeliac is farther back and sends a pan- 

 creaticomesenteric artery above the duodenum, through the ventral 

 pancreas, and along the valvular intestine a gastric to the stomach and 

 the hepatic artery to the liver ; the gastrosplenic and superior mesen- 

 teric arise very near each other. 



The systemic veins all return venous blood to the sinus venosus, 

 which empties into the auricle by way of the sinu-auricular aperture. 

 Hepatic veins lead directly from the liver to the sinus venosus. The 

 ducts of Cuvier collect blood from the anterior cardinals of the head 

 region and posterior cardinals of the trunk region and empty it into 

 the sinus. A hepatic portal system collects from the stomach, in- 

 testines, pancreas, and spleen and empties into the liver. The two 

 renal portal veins bring blood to the kidneys from the single caudal 

 vein of the tail. This blood spreads through the capillaries of the 

 kidneys and is collected into the postcardinals through the renal 



