9 2 



Anatomy of the Rabbit. 



with the lymphatic trunks form extensive plexuses, in connection 

 with which the lymph nodes are distributed. 



THE URINOGENITAL SYSTEM. 



The urinogenital system comprises two primary systems- 

 reproductive and urinary — 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 male 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; k, kidney; od, oviduct; ov, ovary; r, rectum' u. ureter; us, urinogen- 

 ital sinus (vestibulum); ut, uterine tube; v, vagina. Chiefly 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 p rimitive vertebrates (Fig. 49), the urinary and genital ducts 

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



URINOGENITAL DUCTS h this relatI ° n a common canal > the 

 IN VERTEBRATES. cloaca. In terrestrial vertebrates, the 



urinary bladder is devel oped 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 



