COMPARATIVE ANATOMY OF THE CIRCULATORY SYSTEM 237 



along the pancreas supplying the liver, pancreas, and duodenum with many 

 small branches. The posterior pancreatico-duodenal artery enters the right 

 end of the pancreas and passing along the pancreas supplies branches to the 

 liver, pancreas, duodenum, and gall bladder. The third branch of the left 

 aorta is the superior mesenteric artery. It runs posteriorly in the mesentery; 

 trace it, tearing the mesentery, to the center of the coils of the mesentery. At 

 this point the artery breaks up in a fanlike manner into many radiating branches 

 which traverse the mesentery to all parts of the small intestine. One branch, 

 the inferior mesenteric, passes to the large intestine and accompanies it to the 

 cloaca. 



Now follow the left aorta posterior to the point where it gives rise to the 

 superior mesenteric artery. It becomes smaller and very soon meets another 

 vessel coming from the right. The two join in a V-shaped manner and form one 

 vessel, the dorsal aorta, which continues posteriorly in the median dorsal line. 

 Follow the vessel, which meets the left aorta, anteriorly, to discover its identity, 

 Separate the right lobe of the liver from the right lung, and turn the liver and 

 duodenum to the left. The vessel in question can then be traced anteriorly 

 dorsal to the right bronchus and pulmonary vessels to the heart. It is there- 

 fore the right aorta. Immediately beyond its origin from the heart the right 

 aorta gives rise to the large brachiocephalic artery whose branches were followed 

 above. It has no other branches. 



Draw the right and left aortae and the branches of the latter. 



7. The dorsal aorta and the postcaval vein. — The digestive tract may now 

 be removed, except the large intestine which is to be left in place. Follow the 

 dorsal aorta posteriorly. It runs in the median line ventral to some long muscles 

 and in company with the postcaval vein which courses at first to its right and 

 later comes to he ventral to the aorta. We shall study the branches of both 

 vessels. The postcaval vein is seen to be formed by two vessels running along 

 the medial side of the kidneys. Each of these receives numerous renal and 

 genital veins from the kidneys and reproductive organs respectively. The post- 

 caval vein is thus seen to originate between the kidneys. After adding these 

 branches to your drawing of the postcaval vein, the vein may be removed and 

 the dorsal aorta studied. The aorta gives off a number of small branches intc 

 the muscles on which it rests and then passes between the two kidneys. Hold the 

 large intestine backward and clear away the connective tissue from between 

 the two kidneys. The dorsal aorta is seen to give numerous renal arteries intc 

 the kidneys and genital arteries to -the reproductive system. At the posterioi 

 end of the kidneys it forks into the right and left common iliac arteries. 



Separate one kidney from the carapace and press it and the reproductive 

 organs to the other side. Two large arteries will be seen emerging dorsal to the 

 kidney. The anterior one is the epigastric artery; the posterior one, the commor 

 iliac mentioned in the preceding paragraph. Follow the epigastric. (If it was 



