THE ENdLISn SPARROW 387 



enters the left ventricle, whence it is pumped to the tissues. 

 The great artery that carries blood from the left ventricle 

 is called the aorta. It quickly divides into a right and a 

 left branch, from each of which an artery goes to the head 

 with its brain and sense-organs, and to the wings and their 

 great muscles. The right branch of the aorta passes up around 

 the throat and reaches the vertebral column and runs under 

 this (as the dorsal aorta) to the tail. It gives off blood-vessels 

 to the food-canal and its glands, to the legs, to the kidneys, and 

 other organs. The blood which is thus carried by the arteries 

 to various organs of the body breaks up in each of them into 

 capillaries and is finally collected into veins which eventually 

 empt}^, as stated above, into the right auricle. While passing 

 through the capillaries, the Ijlood gives up its oxj^gen and re- 

 ceives from the organs carbon dioxide and other waste products 

 of activity lying in these organs. 



The organs of excretion consist of a pair of bodies of compact 

 form like those of reptiles and mammals, and in striking con- 

 trast to the elongated, segmented kidnej's of Amphibia. This 

 kidney, indeed, represents only the hinder end of the kidney 

 of Amphibia. It is richly sup])lied with blood that carries ex- 

 cretory products which, passing from the l)lood-vesseLs, enter 

 little tubes. These tubules eventuallj' empt}' into a central 

 basin which, in each kidney, connects by a larger tube with 

 the cloaca and the exterior (Fig. 354). 



The Organs and Functions of Reproduction. — In the female 

 the ovary and oviduct of the right side has atrophied ; only 

 that of the left side persists. The eggs grow, in the oviduct, 

 to an enormous extent by the addition of yellow food matter 

 — the yolk. As a j^olk passes down the oviduct a layer of 

 albumin or " white " is poured around it ; next a thin mem- 



