316 ZOOLOGY SECT, xm 



the blood is carried to the head. The two aortic arches curve 

 backwards round the oesophagus, one on the right hand and the 

 other on the left, and meet in the middle line dorsally to form the 

 median dorsal aorta (Fig. 979, d. ao. ; Fig. 980, dors. aort.). From 

 the right arch, just in front of the junction, arise the two subclavian 

 arteries (Fig. 979, s. cl. a.), right and left, each running outwards 

 to the corresponding fore-limb. From the dorsal aorta the first 

 important branch given off is the cosliaco-mesenteric (c. m.). This 

 shortly divides into two trunks, a cceliac (Fig. 980, ccel. a.) supplying 

 the stomach, spleen, pancreas, duodenum, and left lobe of the 

 liver, and an anterior mesenteric supplying the posterior part of the 

 small intestine. Three small posterior mesenteric arteries given off 

 further back supply the large intestine. Posteriorly, after giving 

 off renal and genital branches, and a pair of large iliacs to the hind- 

 limb, the dorsal aorta is continued along the tail as the caudal artery 

 (Fig. 980, caud. art.). Throughout its length, in addition to the 

 larger branches mentioned, the dorsal aorta gives origin to a 

 regularly-arranged series of pairs of small vessels, the intercostal 

 and lumbar arteries, giving off branches that enter the neural canal 

 and others that supply the muscles and integument. 



The venous blood from the tail is brought back by means of a 

 caudal vein (Fig. 979, c.). This bifurcates at the base of the tail to 

 form the two pelvic (lateral) veins (pi.) ; these unite to form the 

 median epigastric or abdominal (ep. g.), which eventually enters 

 the left lobe of the liver. Entering the pelvic veins are the femoral 

 and sciatic veins from the hind-limb. Arising from the pelvic are 

 the renal portal veins distributed to the substance of the kidneys. 

 The efferent renal veins, carrying the blood from the kidneys, combine 

 to form a pair of large trunks, which soon unite to form the median 

 postcaval. The postcaval runs forwards towards the heart, and, 

 after receiving the wide hepatic vein from the liver, enters the sinus 

 venosus. 



Two precavals, right and left, carry the blood from the anterior 

 extremities and the head to the sinus venosus. The right precaval 

 is formed by the union of the internal and external jugular and 

 the subclavian. On the left side the precaval is formed by the 

 union of internal jugular and subclavian, the left external jugular 

 being absent. 



The liver is supplied, as is other Vertebrates, by a hepatic portal 

 system of vessels, blood being carried to it by a portal vein, formed 

 by the union of gastric, pancreatic, splenic, and mesenteric veins. 



The adipose bodies (Fig. 979, c. ad.) are two masses of fat of 

 somewhat semilunar shape in the posterior part of the abdominal 

 cavity, between the peritoneum and the muscles of the body- 

 wall. 



The thyroid is a whitish, transversely-elongated body on the 

 ventral wall of the trachea, a short distance in front of the heart. 



