326 ZOOLOGY sect, xiii 



auricle (venous blood) tends to run more to the riglit-hand 

 portion of the cavity of the ventricle, while that from the left 

 auricle (arterial) occupies the left-hand portion. When the 

 ventricle begins to contract, its walls come in contact with the 

 dorsal and ventral edges of the ventricular partition, thus com- 

 pleting the separation of the right-hand part of the cavity, 

 containing venous blood, from the left-hand part, containing 

 arterial and mixed blood ; and the further contraction results 

 in the driving of the venous blood through the pulmonary artery 

 to the lungs and of the rest through the aortic arches to the head 

 and body. ( Vide Fig. 1002.) 



From the riffht aorta arise the carotid arteries (Fig. 968, cr. ; 

 Fig. 969, car. art.), and each runs for some distance parallel with 

 the corresponding aortic arch, with which it anastomoses distally 

 (the connecting part being termed the ductus Botalli), having 

 previously given off the carotid artery proper, by means of which 

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

 backwards round the cESophagus, one on the right hand and 

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

 form the meAmn dorsal aorta (Fig. 968, rZ. cto. ; Fig. 969, dors.aort). 

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

 subclavian arteries (Fig. 968, 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 cceliaco-mesenteric (c. in.). 

 This shortly divides into two trunks, a cceliac (Fig. 969, cci}l. 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. Pos- 

 teriorly, 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 cccudal ctrtery (Fig. 969, caud. art?). Throughout 

 its length, in addition to the larger branches mentioned, the dorsal 

 aorta gives off 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. 968, f.). This bifurcates at the base of the 

 tail to form the i-wopclvic (lateral) veins {pi.) ; these unite to form 

 the median epigastric or ahdominal {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 j^ostowft/. The postcaval runs forwards 



