COMPARATIVE ANATOMY 55 



the pelvic region, where they are joined by the iliac veins from 

 the fins. 



The hepatic portal system Is made up of all the vessels that 

 carry blood from the digestive organs to the liver. The hepatic 

 portal vein Is formed by the confluence of the veins from the 

 rectal gland, spiral valve, stomach, spleen, and pancreas, and 

 enters the liver dorsal to the median lobe. Within the liver It 

 forms capillaries. The blood leaves the liver by means of the 

 hepatic sinuses. 



The caudal vein enters the body cavity and divides Into two 

 renal portal veins, each of which passes to the dorsal side of a 

 kidney where It gives off small branches Into the kidney. Blood 

 leaves the kidneys through the renal veins that enter the pos- 

 terior cardinal veins. 



Arteries. — Dissect the afferent branchial arteries that extend 

 from the ventral aorta to the gills. How many are there? 

 Remove the mucous membrane from the roof of the mouth and 

 trace the efferent branchial arteries which receive blood from the 

 gills. Follow them back Into the gills as far as possible and 

 observe that they form a series of loops around the margin of 

 the gills. Short horizontal vessels connect the loops with one 

 another. From the first loop arises the common carotid artery. 

 It divides Into external and internal carotids. The internal 

 carotids from the two sides join to form a single vessel, which 

 enters the skull to supply the brain. A coronary artery, arising 

 from one of the efferent branchial vessels, supplies the muscles 

 of the heart and the conus arteriosus with blood. 



Follow the eflFerent arteries inward and posteriorly to where 

 they unite to form the dorsal aorta. This large vessel extends 

 nearly the length of the body. Within the body cavity several 

 vessels arise from the aorta. Sub-clavian arteries extend to the 

 pectoral fins. A coeliac artery, originating just posterior to 

 the transverse septum, supplies stomach, liver, Intestine, and 

 pancreas. Small renal arteries go to the kidneys. An anterior 

 mesenteric to the Intestines and a gastro-splenic to the stomach, 

 pancreas, and spleen arise close together at about the level of 

 the middle of the spiral valve. Further back a posterior mesen- 

 teric goes to the rectal gland. Iliac arteries go to the pelvic fins. 

 Parietal arteries arise along the whole length of the aorta. The 



