6io BIRDS. 



anteriorly in two superior venae cavae, and posteriorly in an 

 inferior vena cava, composed of veins from hind legs and 

 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 off 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 cceliac, mesenteric, 

 renal, femoral, sciatic, iliac, and other arteries. 



(c) The pulmonary arteries (with impure blood) from right ventricle 



to lungs. 



The venous system consists of the following vessels : — 



(a) Two superior venoe cava;, each formed from the union of 

 jugulars from the head, a brachial from the arm, and a pectoral 

 from the breast. 



(b) 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, or hypogastric, 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 pehic 



region ; thus the hypogastric is formed, which parsing upw^ards 



through the kidney receives the sciatic, and finally joins with 



the femoral and with the renal. 



((.•) The pulmonary veins, with pure blood, from lungs to left auricle. 



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. 



A functional 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 hypogastrics or by 

 the division of the caudal vein, a coccygeo-mesenteric arises, which 

 receives vessels from the cloaca and large intestine, and is continued 

 along the mesentery to join the hepatic portal system. 



As there are rarely any valves in the renal portal veins, the blood 

 from the viscera and hind limbs can pass freely either through the iliac 

 veins and thence to the inferior vena cava, or through the coccygeo- 

 mesenteric vein to the hepatic portal system. 



The epigastric vein of the bird takes blood from the fat-laden sheet 



