414 



COIkCPARATIVE ANATOMY 



fusion of the uteri are represented in the placental mammals — uterus 

 duplex, bipartitus, bicornis, and, in primates, uterus simplex. Even 

 in the primates, however, the original duplex character of the Muellerian 

 ducts is retained in the paired uterine tubes. (Fig. 339) 



External genital organs also make their appearance in mammals. 

 Copulatory organs are, however, not wholly new in this group. Some 

 of the flatworms have an intromittent organ by which sperm is conveyed 



Fig. 340. — Diagrams of male urogenitalia in I, monotreme; II, marsupials; and III, 

 monodelphs. a, anus; b, bladder; c, cloaca; cm, corpus cavernosum urethrae; c/), corp. 

 cav. penis; cd, Cowper's gland; p, perineum; pg, prostate gland; r, rectum; s, symphysis 

 pubis; t, testis; u, ureter; v, vas deferens; vg, vesicular gland; vm, ventral muscles. 

 (Prom Kingsley's "Comparative Anatomy of Vertebrates," after Weber.) 



to the seminal receptacle of another individual. In elasmobranchs, 

 the pelvic fins of the male are modified as claspers which in copulation are 

 inserted into the cloaca of the female. None of these structures however 

 are morphologically comparable with the phallus of mammals. 



The free posterior extremity of the paired erectile folds in the floor 

 of the cloaca of chelonia forms a glans. 



In monotremes likewise, the phallus points posteriorly and is contained 

 in the floor of the cloaca. In the walls of the monotreme cloaca, the 

 seminal groove of the reptile has become a tubular canal surrounded by 

 erectile tissue, the corpus cavemosum urethrae. This canal is used in 



