VASCULAR SYSTEM OF THE PIGEON. 513 



kidneys, and receiving as it approaches the heart the hepatic 

 veins from the liver. 



The right auricle of the heart is larger than the left ; the 

 right ventricle has thin walls, and partly surrounds the 

 more muscular left ventricle. 



The arterial system consists of the following vessels : — 



(a) The arterial trunk, as it rises from the heart, gives 



off on each side an innominate artery. Each 

 innominate gives oif a carotid and a subclavian, 

 and the subclavian immediately divides into a 

 brachial to the arm and a pectoral to the breast 

 muscles. 



(b) The dorsal aorta, formed by a continuation of the 



arterial trunk bending round on the right side, 

 gives off coeliac, mesenteric, renal, femoral, sciatic, 

 iliac, and other arteries. 



The venous system consists of the following vessels : — 

 (a) Each superior vena cava is formed from the union 

 of jugulars from the head, a brachial from the arm, 

 and a pectoral from the breast. 

 (V) The inferior vena cava is formed from the junction 

 of two iliac veins just in front of the kidneys. 

 Each of these iliacs results from the union of a 

 femoral from the leg, an efferent renal from the 

 kidney, and a renal portal which passes upwards 

 through the kidney. To understand this renal 

 portal, it is convenient to begin at the tail. A short 

 caudal vein divides anteriorly into right and left 

 branches, each of these receives an internal iliac 

 from the sides of the pelvic region j thus a hypo- 

 gastric or renal portal is formed, which passing 

 upwards through the kidney receives the sciatic, 

 and finally joins with the femoral and the renal. 



The hepatic portal system is as usual : — mesenteric veins 

 from the intestine combine in portal veins; the blood 

 filters through the liver ; and is collected in hepatic veins, 

 which unite with the anterior end of the inferior vena cava. 



The renal portal system is represented by branches which 

 the femoral and sciatic give off to the kidney. 



From the transverse vein formed between the two hypo- 

 2 K 



