UROGENITAL SYSTEM 



821 



separation of the faecal and urogenital matter. This separation is 

 brought about by a horizontal partition dividing the cloaca into a dorsal 

 rectum and a ventral urogenital portion. This space between rectum 

 and urogenital portion is called the perineum. 



us. 



Fig. 462. 



E, The urogenital organs of a female pigeon. K., kidney (metanephros) 

 with three lobes ; u., ureter ; cl., cloaca ; ov., ovary ; od., oviduct ; f.t., funnel at 

 end of oviduct ; r.r.od., rudimentary right oviduct. 



F, The urogenital organs of a male pigeon. T., testes ; V., base of inferior 

 vena cava ; S.R., suprarenal glands; K., kidneys with three lobes (1, 2, 3); 

 u., ureter; v.d., vas deferens ; v.s., seminal vesicle; cl., cloaca. (A, B, C, D, from 

 Borradaile, E, F, from Thomson.) 



ORGANS OF COPULATION. 



In both sexes of mammals the same anlagen of the external genitalia 

 are found as already studied in embryology. These consist of a 

 genital prominence which is formed from the ventral or anterior wall of 

 the cloaca. This then protrudes from the opening and, when the per- 

 ineum is formed, two thickenings appear on each side, a medial genital 

 fold and a larger and lateral genital ridge, which extends back nearly to 

 the level of the anus. The genital prominence never develops much 

 farther in the female, while the folds and ridges become the labia minora 

 and majora. In the male, however a groove is formed on the primitively 

 dorsal surface of the prominence which continues into the cloaca. Then 

 the folds grow together behind the prominence, closing the groove to a 

 tube, the urethra, while the prominence becomes the glans penis. A 

 similar growth of the genital ridges toward the median line results in 

 the formation of the outer wall of the scrotum. 



