xni PHYLUM CHORDATA 665 



The ureters in all the Theria open into a large median sac the 

 urinary bladder situated in the posterior or pelvic part of the 

 cavity of the abdomen. From this a median passage, the urino- 

 genital passage or urethra into which in the male the vasa deferentia 

 open leads to the exterior. Only in the Monotremes do the two 

 ureters and the bladder all have separate openings into the urino- 

 genital division of the cloaca. 



The testes are oval bodies, which only exceptionally retain their 

 original position in the abdominal cavity, descending in the 

 majority of Mammals through a canal the inguinal canal in the 

 posterior part of the abdominal wall to lie in the perinceum, or 

 space between the urinogenital and anal apertures, or to be received 

 into a pendulous pouch of skin, sometimes double the scrotum. 

 The penis, present in the males of all Mammalia, consists of two 

 corpora cavernosa, firm strands of vascular tissue, attached proxi- 

 mately to the ischia except in the Monotremes, Marsupials, and some 

 Edentata, and a central strand, the corpus spongiosum, perforated 

 by the urethral canal and often dilated at the extremity to form 

 the glans. The two vasa deferentia continued from the epididymes, 

 which are in close relation to the testes, join the urethral canal near 

 the neck of the bladder, each often having connected with it, near 

 its distal end, a sacculated reservoir the vesicula seminalis. A 

 small diverticulum of the proximal part of the urethra the uterus 

 masculinus may be a remnant of the Miillerian duct. Surrounding 

 this part of the urethra is a glandular mass the prostate gland ; 

 and the ducts of a pair of small glands Cowper's glands open 

 into the urethra near the base of the penis. 



The ovaries are compressed oval bodies which retain their primary 

 position in the abdomen, or pass backwards into its posterior or 

 pelvic part. In the Monotremes, large Graafian follicles project on 

 the surface of the ovary, while in other Mammals the Graafian 

 follicles are very small, and the surface of the ovary almost smooth. 



The oviducts have dilated funnel-like abdominal openings, the 

 edges of which, except in the Monotremes, are fimbriated or fringed. 

 In the Monotremes the two oviducts are distinct throughout their 

 length, and open separately into a urinogenital sinus. In nearly 

 all the Theria more or less coalescence takes place. In the Marsupials 

 this coalescence is confined to the proximal part of the vagina. In 

 the Opossums (Fig. 1223, A) the two oviducts are merely in close 

 apposition at one point behind the uteri, and there is no actual 

 coalescence. In the rest of the Marsupials (B, C) the anterior 

 portions of the oviduct in the region (vagina) behind the uteri unite 

 to form a median chamber which may send backwards a median 

 diverticulum (median vagina, Vg., B), and in this way communicate 

 behind with the urinogenital passage. In the Eutheria there is a 

 single median vagina (Fig. 1224, Vg.) formed by the union of the 

 posterior parts of the two oviducts. In some cases the two uteri 



