26 LABORATORY STUDIES IN ZOOLOGY 



whole length of the lung, gives off branches to its walls. When 

 labeling this arch on any of the drawings state the region which 

 it supplies. 



3. The aortic arch (Fig. 1, II), the middle of the three main 

 divisions, extends somewhat obliquely around the esophagus 

 to its dorsal side and unites with its fellow of the opposite side 

 at about the level of the cephalic end of the kidney to form a 

 single vessel, the dorsal aorta. In order to expose the dorsal 

 aorta pierce the peritoneum about the left kidney and gently 

 pull the kidney away from the body wall so as to expose the large 

 lymph space in which this vessel runs. The aortic arch and its 

 branches in the region of the pectoral girdle can best be studied 

 from the side. 



Before the union of the two arches to form the dorsal aorta 

 there are at least four branches given off, but attention is drawn 

 to one only, the large subclavian artery which arises at about the 

 level of the shoulder and extends laterad to supply the arm. 



Branches given off after the union of the two arches to form the 

 dorsal aorta are: 



a. The cceliaco-mesenteric artery, a large median vessel arising 

 near the union of the two arches, or sometimes from the left 

 arch just before the union, and supplying the stomach and 

 intestines. This vessel in its turn gives rise to two important 

 branches: (1) the common coeliac artery, whose branches supply the 

 stomach, liver, and gall bladder; and (2) the mesenteric artery, 

 whose branches supply the intestine and spleen. 



b. The urogenital arteries, four to six in number. These are 

 small vessels which arise from the ventral surface of the dorsal 

 aorta between the kidneys. They supply the kidneys, the 

 reproductive organs and their ducts, and the fat bodies. There 

 are other small arteries leaving the dorsal aorta, but the study of 

 these may be omitted. 



c. The common iliac arteries are large vessels formed by the 

 division of the dorsal aorta near the level of the caudal end of 

 the kidneys and are distributed to the legs. Cut the muscle 

 mass on either side of and along the urostyle, which can then be 

 elevated and removed along with the attached muscles. Trace 

 the artery in its course down the leg. 



A recently etherized frog is necessary for the study of the veins. 

 If the veins are injected the venous system should be studied 

 first. 



