498 



THE MALE GENITAL ORGANS OF THE HORSE 



the pelvis, turns around the ischial arch, forming an acute angle, and passes forward 

 inclosed in the corpus spongiosum. It may, therefore, be divided into two seg- 

 ments, pelvic and extrapelvic. 



The pelvic part (Pars pelvina) is four or five inches (ca. 10 to 12 cm.) long. 

 At its origin it is not distinguishable from the neck of the bladder in size or structure; 

 in fact no line of demarcation exists between the two. Behind the prostate the 

 tube dilates to a potential width of two inches or more (ca. 5 to 6 cm.). Near the 

 ischial arch, l^etween the ])ulbo-urethral (Cowper's) glands, it contracts again, 

 forming the isthmus urethras. It is related dorsally to the rectum and the prostate, 

 ventrally to the internal obturator muscles, and laterally to the bulbo-urethral 



Lateral lobe of 'prostate 



Orifice of uterus mascnlinus 



Ducts of urethral glands 



CoUicuIus sc7ninalis 



Duels of bulbo-urethral 

 {Cowper's) (jlands 



Fig. 398. 



-Pelvic Urethra and Posterior Part of Bladder of Horse Slit Ventrally and Laid Open. 



e.d., Kjaculatory ducts. 



glands. It is inclosed, except at its origin, by the urethral (Wilson's) muscle. 

 Beneath this is a rich venous plexus, forming a sort of erectile tissue.^ 



Th(> extrapelvic part (Pars cavernosa) passes between the two crura of the 

 penis and runs along Ihe groove on the ventral surface of the corpus cavernosum 

 penis, inclosed by the cori:)us spongiosum and the bulbo-cavernosus muscle. It 

 passes through the glans penis and projects forward about an inch in the fossa 

 glandis as a free tube, the processus urethrae ; this part is covered by a delicate 

 integument, under wiiicii there is a thin layer of erectile tissue. 



' It has boon customary to divide tlio pelvic part of the urethra into pro.static and mem- 

 branous parts. These terms apply well in human anatomy, but have no special value in com- 

 parative anatomy. In the horse :i j)i()sfatic part hardly exists, unless we a.ssume that it and the 

 neck of the liladder together are only about an inch in length. There is no membranous part in 

 the sense in which that term is used in regard to man. 



