448 



Vertehrata. 



arch (left arterial arch of the second pair), which arises in Crocodiles 

 from the right ventricle, is here altogether absent; the aorta is 

 thus exclusively formed by the right ardh arising from the left 

 ventricle; in other respects the relations are like those of the 

 Crocodiles. No mixing of arterial and venous blood occurs in Birds ; 



aa 



Pig, 375. Diagram of the heart and arterial arches of a Crocodile {A) and of a 

 Bird (B). a right, a' left auricle; v right, v' left ventricle; ao aorta. 1, 2, 4 1st, 2nd, 

 and 4th arterial arches of the right side, 1' 2' 4' the same of the left side (c and m 

 see Fig. 347). — Orig. 



the venous blood enters the right auricle, goes thence into the right 

 ventricle, and from the latter to the lungs ; the arterial blood from 

 the lungs goes to the left auricle, thence to the left ventricle, and so 

 into the body. 



The kidneys are long, dark-red bodies lying in the pelvic 

 region , just below the vertebral column ; they occupy the spaces 

 between the transverse processes, and are divided ventrally by 

 transverse constrictions into several (usually three) lobes. Sometimes 

 the two glands fuse, to a greater or less extent, along their inner 

 edges. The ureters open separately into the cloaca; a urinary 

 bladder is absent. The urine is semi-solid and whitish. 



Of the ovaries, only the left is developed ; exceptionally 

 there is however a rudimentary right one; in many diurnal Birds of 

 Prey (Falcon, Sparrow-hawk, Buzzard) such a rudiment is large 



