246 LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



next from the dorsal aorta; it supplies the middle and posterior lobes of the 

 kidney, then proceeds to the lateral body wall, and as the femoral artery supplies 

 the leg. It may be followed by turning the animal dorsal side up and looking 

 between the muscles of the thigh along the course of the femoral vein previously 

 identified. The femoral artery accompanies the large sciatic nerve and branches 

 into the leg muscles. Returning to the peritoneal cavity, trace the dorsal aorta 

 further. As it passes between the kidneys it gives off lumbar arteries into the 

 dorsal body wall. At the posterior end of the kidneys it forks. At the point 

 of forking arise the inferior mesenteric artery, which runs anteriorly in the 

 mesorectum and anastomoses with a branch of the superior mesenteric artery, 

 and the caudal artery, which proceeds straight posteriorly in the median line to 

 the tail. The two forks of the dorsal aorta are named the internal iliac arteries. 

 They pass posteriorly along the roof of the pelvic region. The left one gives 

 off branches into the oviduct. 



Draw the branches of the dorsal aorta. 



6. The structure of the heart. — Free the heart by cutting across the great 

 vessels. Note that all veins enter the apparently anterior end of the heart, hav- 

 ing shifted forward out of the transverse septum. As already stated, there is 

 neither sinus venosus nor conus arteriosus in the bird's heart. Only two of the 

 original four chambers of the heart have persisted, namely, auricle and ventricle, 

 but each of these is subdivided into two completely separate halves, the right 

 and left auricles and ventricles. The auricles are small thin-walled chambers 

 anterior to the ventricles. In the walls of the right auricle identify the openings 

 of the systemic veins and in the left auricle of the pulmonary veins. Slit open 

 the right auricle and looking within note the thin inter auricular septum separating 

 it from the left auricle. A fold extends from this septum to the entrance of the 

 postcaval vein partly concealing the entrance. Note the deep cleft, the auriculo- 

 ventricular opening, through which the right auricle opens into the right ventricle. 

 Similarly open the left auricle and find the left auriculo-ventricular opening. 

 Cut across the apex of the ventricles. Observe the crescentic form and relatively 

 thin walls of the right ventricle and circular section and enormously thickened 

 wall of the left ventricle. What appears to be the internal wall of the ventricles 

 is the interventricular septum, completely separating the cavities of the two ven- 

 tricles. Open the right ventricle by a slit extending from the previously cut 

 apex to the base. Note the single valve which guards the right auriculo-ventricular 

 opening; it is a muscular band extending from the ventricular wall to the 

 auriculo-ventricular opening. In the left side of the anterior end of the right 

 ventricle find the opening of the pulmonary artery, or probe into the base of 

 the pulmonary artery and note emergence of the probe into the right ventricle. 

 At the base of the pulmonary artery are three pocket-like semilunar valves. Cut 

 into the left ventricle and note the two thin membranous valves which guard 

 the auriculo-ventricular opening. They are called the mitral valve. Each is 



