92 



Anatomy of the Rabbit. 



with the lymphatic trunks form extensive plexuses, in connection 

 with which the lymph nodes are distributed. 



THE URIWOGENITAL SYSTEM. 



The urinogenital system comprises two primary systems — 

 reproductive and virinary — differing widely in their central organs, 

 but associated to a certain extent by having common ducts. In 

 the rabbit, as indicated in the accompanying diagram (Fig. 48), 

 this association extends only to the presence in the two sexes of a 

 urinogenital canal, or urinogenital sinus connecting both urinary 

 and genital structures with the outside of the body. This canal is 

 designated in the rriale as the urethra, but in the female as the 



Fig. 49. The principal stages in specialization of the female urinogenital 

 ducts in vertebrates. A, frog; B, monotreme; C, marsupial, bl, bladder; 

 cl, cloaca; Ic, Icidney; od, oviduct; ov, ovary; r, rectum* u, ureter; us, urinogen- 

 ital sinus (vestibulum) ; ut, uterine tube; v, vagina. .Chiefiy from figures of 

 Gegenbaur and Wiedersheim. 



vestibulum, since the structure known from the human relation 

 as the female urethra is only a urinary canal leading from the 

 bladder, and in man is not associated with the reproductive ducts. 

 In primitive vertebrates (Fig. 49), the urinary and genital ducts 

 open into the posterior end of the digestive tube, the latter forming 



in this relation a common canal, the 

 cloaca. In terrestrial vertebrates, the 

 urinary bladder is developed as a ventral 

 outgrowth of the digestive tube, and, except in amphibians, both 

 sets of ducts undergo a migration from their original position on 

 to the wall of its canal, the latter being thus trasfnormed into a 



URINOGENITAL DUCTS 

 IN VERTEBRATES. 



