COLUMBA. 



367 



heart. Here it bends into the middle line and proceeds to 

 the hind-end of the body as the dorsal aorta. Its main 

 branches are coiliac^ anterior mesenteric^ paired renals, 

 femorals, sciatics and ifiternal iliacs, and it terminates in 

 the tail as the caudal artery. 



Fig. 259.— Ventral View of the Arterial System 

 OF THE Pigeon. [Ad nat.) 



Carotid. 



•Vertebral. 



Brachial. 



Systemic Arch, 



Dorsal Aorta, 



Internal Iliac. 



Caudal. 



Pectorals. 



Innominate (left). 



Coeliac. 

 Anterior 



Mesenteric. 

 Renal. 



Femoral. 

 Sciatic. 



Internal Iliac. 



Posterior 



Mesenteric. 



The anterior arterial system is peculiar in lying super- 

 ficially to the venous system. Apart from the four- 

 chambered heart, which is shared by mammals, the blood- 

 vascular system of the pigeon is chiefly remarkable for 

 the very high temperature of the blood, the systemic arch 

 persisting only on the right, and the large size of the 

 pectoral arteries and veins. 



If the heart be now removed, the trachea can be traced 

 throughout its length till it bifurcates into the two bronchi. 

 At its front-end is a larynx which, however, is not an organ 

 for producing sounds in the bird. The trachea is distended 



