THORAX AND ABDOMEN OF THE HORSE 



79 



flush with, or even slightly beyond, the surface of the glans. The fossa 

 is deepest above the urethral process. 



The surface of the glans, the interior of the fossa glandis, and the 

 outer surface of the urethral process are covered by thin, hairless skin, 

 continuous with the innermost layer of the prepuce and merging into 

 the urethral raucous membrane at the external urethral orifice. 



A short, rounded and well-developed inchio- caver nous muscle 

 (ni. ischiocavernosus) covers each crus of the penis, taking origin from 

 the most lateral part of the sciatic arch and the adjacent portion of the 

 sacro-tuberous ligament, and ending on the tunica albuginea of the 

 corpus cavernosum penis. Each ischio-cavernous muscle and the 

 crus penis that it covers are accommodated in a deep depression in the 

 origin of the semimembranosus muscle. 



Processus dorsalis glandis, 



Corpus cavernosum penis. : 



Dorsal vein. ; I 



Visceral layer of prepuce. 

 \ Fossa glandis. 



\ I Glans. 



M. bulbocavernosus. 



i 

 Corpus cavernosum urethrae 



Urethral process. 

 I Urethra. 

 Parietal layer of prepuce. 



Fig. 36. — Extremity of the penis. A sagittal section of the glans has been made, 

 and the terminal portion of the corpus cavernosum penis exposed. 



The penile portion of the urethra is covered by the bulbo-cavernous 

 muscle (m. bulbocavernosus), a continuation of the urethral muscle of 

 the pelvis. It may be considered that this muscle begins at the bulbo- 

 urethral glands (to be examined with the pelvic contents) and extends 

 all along the penis to the glans. For the most part, the muscle 

 consists of transverse fibres connected with the tunica albuginea along 

 the margins of the groove in which the urethra is lodged, and 

 consequently covers three surfaces of the corpus cavernosum urethrse ; 

 but in the region of the root of the penis, where the muscle is thicker 

 than elsewhere, it forms a complete investment of circular fibres 

 surrounding the urethral corpus cavernosum. 



Two parallel pale muscular bands appear to begin in the region of 

 the anus, though their fibres may be traced to the first and second 



