Sauropsida: Class Aves 



531 



dorsally into the proctodeum (although apparently the embryonic 

 origin of the bursa is from endoderm). In adults the bursa is much 

 reduced or entirely absent. Its function is not definitely known. 



Fig. 413. (A) Genitalia of hen. (B) 

 Cloacal region of cock, (a) Albumen-secret- 

 ing region of oviduct; (/) discharged follicle 

 of ovary; (o) advanced ova in follicles; (ol) 

 ostium tubae abdominale; (r) rectum; (s) 

 openings of vasa deferentia; (u) urinary 

 openings; (ut) uterus or shell-gland with 

 the villi showing in the opening; (») cloacal 

 opening of left oviduct. (After Tichomiroff. 

 Courtesy, Kingsley: "Comparative Anat- 

 omy of Vertebrates," Philadelphia, The 

 Blakiston Company.) 



Urinogenital Organs 



The kidneys of birds are metanephric, as in reptiles. From each 

 metanephros the ureter passes directly into the urodeum (Fig. 413). 

 There is no urinary bladder — another point where the bird omits 

 useless weight. But it must be remembered that some reptiles omit the 

 bladder, and without the good reason which birds seem to have for 

 doing so. 



The reproductive organs of the male have no unusual features. 

 Right and left testes and vasa deferentia (sperm-ducts) are fully de- 



