THE URINOGENITAL SYSTEM 199 
rectum. The sphincter ani externus and sphincter ani internus are two 
closely related muscles enclosing the rectum and urethra, the former arising from 
the dorsum of the tail. 
The following parts of the urinogenital system may be made out: 
(a) The connection of the bladder wich the outside of the body 
through the urethra. It comprises a short prostatic 
portion in relation to the genital ducts, a much longer 
membranous portion traversing the pelvis, and a terminal 
cavernous portion in the penis. 
(b) The seminal vesicle (vesicula seminalis) lies on the dorsal 
surface of the base of the bladder. It is a flattened median 
pouch, the anterior, slightly divided tip of which is directed 
forward. 
(c) The deferent ducts lie between the seminal vesicle and the 
dorsal wall of the bladder. They terminate in the ventral 
wall of the seminal vesicle. 
(d) The prostate (prostata), a white or yellowish mass of 
glandular tissue, lies in the posterior portion of the dorsal 
wall of the seminal vesicle. Its ducts, three or four in 
number on either side, open into the urethra. Accessory 
paraprostatic glands (gl. paraprostaticae), minute finger- 
like projections of the urethral wall, lie on either side of the 
base of the seminal vesicle. 
(e) The bulbourethral gland (1. bulbourethralis) ; situated on 
the dorsal wall of the urethra behind the prostate. 
3. The internal surface of the dorsal wall of the urethra may be 
exposed by a longitudinal incision extending into the bladder. The 
crescentic aperture of the seminal vesicle lies immediately in front 
of an oval elevation, the colliculus seminalis, on either side of 
which some of the minute apertures of the prostate may sometimes 
be made out. 
C. The Female Genital Organs. 
1. The organs may be traced from the abdominal cavity back- 
ward, as follows: 
(a) The ovary (ovarium) is a small—in young animals minute— 
elongated structure of greyish or yellowish coloration lying 
