COMPARATIVE ANATOMY OF THE CIRCULATORY SYSTEM 25; 



right side passing dorsal to the postcaval, and in the rabbit those of the lef 

 side to the dorsal side of the left precaval. They convey the aerated blood fron 

 the lungs into the left auricle. 



5. The pulmonary artery.— The pulmonary artery is the conspicuous vesse 

 extending from the base of the right ventricle forward between the auricles- i 

 soon curves to the left. Its base is generally surrounded by fat, which shoulc 

 be cleaned away. It divides in two at the turn into right and left pulmonar 

 arteries. The division may be found by dissecting along the pulmonary arten 

 immediately in front of the left auricle. Press the heart to the right and follov 

 the left pulmonary artery into the left lung. In the rabbit it passes to the dorsa 

 side of the left precaval vein which may now be severed. The left pulmonan 

 artery courses parallel to and anterior to the most anterior of the pulmonary 

 veins. Now turn the heart to the left and similarly find the right pulmo 

 nary artery proceeding to the right lung; to trace it sever the precaval vein. I 

 lies immediately anterior to the foremost pulmonary vein. Dorsal to the riglr 

 pulmonary artery lies the trachea. 



6. The aorta and its branches. — Springing from the base of the left ventrich 

 to the left of and dorsal to the pulmonary artery is a very large trunk, the aorta 

 Right and left coronary arteries spring from the base of the aorta where it leave; 

 the ventricle. The left coronary artery lies between the pulmonary artery anc 

 the left auricle, and branches over the ventral and left side of the heart. The 

 right coronary artery lies along the groove between the right auricle and righi 

 ventricle and branches to the right and dorsal surfaces of the heart. 



Follow the aorta forward, cleaning away tissue from its surface. It soor 

 describes a curve, known as the arch of the aorta, to the left. From the arch o: 

 the aorta spring the large arteries of the neck, head, and fore limbs. These an 

 two in number in the cat, three in the rabbit. Beginning at the right they an 

 in the rabbit: the brachiocephalic or innominate artery; the left common carotid, 

 and the left subclavian. In the cat the branches are the brachiocephalic 01 

 innominate artery to the right and the left subclavian to the left. The difference 

 is due to* the fact that in the cat, as in man, the left common carotid branches 

 from the brachiocephalic, and this may also occur in the rabbit as a variation 



Trace the brachiocephalic artery forward. The precaval vein and it: 

 branches may be removed. The artery gives off small branches into the thymus 

 gland and trachea lying dorsal to it and then divides into two branches in the 

 rabbit and three in the cat. These are : right subclavian and right common carotic 

 in the rabbit, and right subclavian, right and left common carotids in the cat 

 Each of these will be traced separately. 



a) Subclavian artery: Trace the right subclavian; both have identica 

 branches. 



Rabbit: From the posterior surface of the subclavian arises the interna 

 mammary artery which follows the vein previously described along the ventra 



