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 distinguishal)le 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, between the l)ulbo-urethral (Cowper's) glands, it contracts again, 

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

 ventrally to the internal ol)turator muscles, and laterally to the bulbo-urethral 



Lateral lobe of 'prostate 



Orifice of uterus tnasculiv 



Ducts of uretJtrul glands 



Collicvlns scminalis 



Ducts of hulho-itrethral 

 {Cowper^s) glands 



Fig. 398. — Pelvic Urethra and Posterior Part of Bladder of Horse Slit Ventrally and Laid Open. 



e.d., Ejaciilatory duets. 



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.^ 



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

 penis and runs ahjug the groove on the ventral surface of the corpus cavernosum 

 penis, inclosed by the corpus spongiosum and the liulbo-cavernosus nmscle. It 

 passes througli 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 which there is a thin layer of erectile tissue. 



1 It luus been eu.stoni;iry to divide the pelvic part of the urethra into prostatie and mem- 

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

 parative anatomy. In the horse a prostatic part hardly exists, unless we assume that it and the 

 neck of the bladder 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. 



