970 GENERATIVE APPARATUS. 



fluid which is thrown into the urethra.^ (This third vesicula is present in all the 

 domesticated animals.) 



The ejaculatory ducts may become obliterated ; then the secretion of the 

 vesiculae seminales accumulates in their interior, and gradually distends them 

 until they attain enormous dimensions. We found, in a Gelding, a vesicula 

 which was nearly as large as the bladder ; it contained a brownish, adhesive fluid, 

 holding in suspension epithelial cells and free nuclei. 



(The vesiculae seminales, in addition to tiieir own secretion, receive the semen 

 conveyed by the spermatic ducts, and keep it in reserve until copulation ; when 

 the contraction of its muscular apparatus expels it into the ejaculatory ducts, 

 and from these into the urethral canal.) 



3. The Urethra. 



The urethra is a canal with membranous and erectile walls, commencing at 

 the neck of the bladder, and terminating at the free extremity of the penis. 



Course. — When followed from its origin to its termination, it is seen to 

 proceed at first horizontally backwards, then bend downwards at the ischial arch 

 to leave the cavity of the pelvis, placing itself between the two roots of the 

 corpus cavernosum, and passing forward in the channel formed at the lower 

 border of these, until it arrives at the head (glans) of the penis, where it termi- 

 nates by forming a small (cylindrical) prolongation, named the urethral tube. 

 In its track, the urethra is divided into two very distinct portions : the intra-pelvic 

 — the shortest, and the extra-pelvic — the most extensive, and which is supported 

 by the corpora cavernosa. The latter division, being alone enveloped by the 

 erectile tissue that enters into the formation of the urethral walls, has been also 

 named the spongy portion, the first being designated the membranous (and pro- 

 static) portion. 



Interior. — Internally, this canal has not the same width throughout. Very 

 constricted at its origin, towards the neck of the bladder, it expands somewhat 

 suddenly at the prostate gland ; its dilatation, improperly named in Man the 

 cul-de-sac of the bulb (bulbous portion), or, better, the ventriculus, extends to its 

 curve over the ischial arch, where it gradually contracts. After this it preserves 

 the same reduced dimensions throughout its course, though these dimensions may 

 be increased during the passage of the urine or semen. There is, however, 

 behind the urethral tube a small oval dilatation, named the fossa navirularis 

 (Fig. 524). Smooth throughout its extra-pelvic portion, the inner surface of the 

 urethra offers, near the neck of the bladder, and on its upper wall, the excretory 

 orifices of the prostate gland, which form two lateral lines of minute perforated 

 tubercles. Between these two lines is found the urethral ridge or verumontanum 

 {caput galUnaginus), a httle eminence elongated from before to behind, on the 

 sides of which the ejaculatory ducts open. Behind this are the excretory orifices 

 of Cowper's glands. 



Relations. — The intra-pelvic portion of the urethra is in relation, above, with 

 the prostate, which adheres closely to it, and with the rectum, to which it is 



' In some Asses, we have found this pouch bifurcated at its anterior extremity, and there- 

 fore bearing a distant resemblance to the female uterus. 



(Though Chauveau states that the protometra is improperly named the male uterus, it would 

 appear, nevertheless, that the designation is correct ; as this pouch is not a gland in the 

 ordinary sense of the term, and is certainly the rudiment of the duct which develops into the 

 uterus in the female.) 



