VASCULAR SYSTEM. 



609 



from the liver, which is without a gall bladder, though this 



is present in most birds. 



The small intestine is long; the large intestine is very 



short ; in fact, it is not more than a rectum two inches in 



length. At the junction of the small and the large intestine, 



there are two short caeca. In 

 some birds, e.g., the fowl, these 

 are of considerable length. 



The cloaca has three divisions, 

 an upper part into which the 

 rectum opens, a median part 

 into which the ureters and the 

 genital ducts open, and a pos- 

 terior region opening into which 

 from the dorsal surface is a vas- 

 cular and glandular sac called 

 the bursa Fabricii, which usually 

 disappears during adolescence. 

 Its function is obscure. 



Vascular System. 



The four-chambered heart, the 

 single aortic arch bending over 

 to the right side, the hot blood, 

 are the most important char- 

 acteristics. 



The impure blood having re- 

 turned by the venae cavae to the 

 right auricle, passes through the 

 auriculo-ventricular valve, which 

 has two muscular flaps, into the 

 right ventricle, and is thence 

 driven to the lungs. From the 

 lungs, the purified blood returns 

 to the left auricle, and passes 

 through two membranous valves 

 into the left ventricle. Thence 

 it is driven through the arterial trunk into the carotids, 

 the subclavians, and the dorsal aorta. The bases of the 

 aortic and pulmonary trunks are guarded by three semilunar 

 valves. From the capillaries, the impure blood is collected 

 39 



FIG. 215. Circulation of 

 Pigeon. (From PARKER, 

 see Preface.) 



ra, Right auricle ; la, left 

 auricle ; P, pulmonary artery ; 

 C, carotid artery ; Br.a, brachial 

 artery ; PC. a, pectoral artery ; 

 j, Jugular vein ; Br. v, brachial 

 vein ; PC. v, pectoral vein ; ao, 

 aorta ; h v, hepatic veins ; i v c, 

 inferior vena cava ; d , dorsal 

 aorta ; zY, iliac artery and vein ; 

 r p, renal portal or hypogastric ; 

 sc, sciatic artery and vein ; r z>, 

 renal vein ; J?, femoral vein ; c m, 

 coccygeo-mesenteric to liver. 



