292 THE ANATOMY OF THE HORSE. 



attached under cover of the erector penis muscle. These constitute the 

 roots, or crura, of the penis, and they converge towards each other and 

 form a single mass which makes up the main thickness of the penis as 

 far as the glans. The united corpora cavernosa have an upper flattened 

 surface, or dorsum, along which the dorsal vessels and nerves pass. 

 Their sides are smooth and slightly rounded, and inferiorly they form a 

 shallow median groove for the corpus spongiosum (Fig. 40). Anteriorly 

 they terminate bluntly in the glans. 



The Corpus Spongiosum forms a much more slender column than the 

 corpora cavernosa. It is traversed in the whole of its length by the 

 extra-pelvic part of the urethra. This urethra, as will subsequently be 

 seen, begins at the neck of the bladder, and its first few inches are 

 intra-pelvic, being placed over the ischiatic symphysis. Turning round 

 the ischial arch, the intra-pelvic urethra becomes directly continuous 

 with the extra-pelvic portion, and from the point of continuity onwards 

 the urethra is enveloped in a sheath of erectile tissue, which is the 

 corpus spongiosum. The corpus spongiosum forms at either of its 

 extremities an enlargement. The posterior enlargement, which is 

 situated at the ischial arch, is termed the bulb ; the anterior enlarge- 

 ment is the glans penis. The glans forms the expanded free extremity of 

 the penis, and it surrounds the blunt anterior end of the united corpora 

 cavernosa. During erection the enlargement assumes a shape resem- 

 bling, somewhat, the rose of a watering-can, having a prominent ridge — 

 the corona glandis, behind which there is a slight constriction — the 

 cervix. The front of this rose-like swelling presents a fossa from which 

 the urethra projects for about half an inch as a free tube — the urethral 

 tube. Above the base of the urethral tnbe there is the opening of a 

 double cavity — the urethral sinus, which generally contains some of the 

 partially inspissated secretion of sebaceous glands that open into the 

 cavity. Inferiorly the corona glandis is interrupted on the middle line 

 by the suburethral notch. 



The corpus spongiosum as far as the glans is surrounded by the 

 accelerator urinse muscle. Superiorly it fits into the groove on the 

 lower aspect of the corpora cavernosa, and along its under aspect pass 

 the retracter muscles of the penis. 



Directions. — Immediately in front of the junction of its crura, the 

 penis should now be amputated, in order that the structure of its 

 component parts may be examined. 



Structure of the corpora cavernosa. The corpora cavernosa possess 

 a strong envelope of white fibrous tissue, termed the tunica albuginea. 

 This tunica albuginea, besides forming a common envelope to the united 

 bodies, sends inwards an incomplete mesial septum between the two — 

 the septum pectiniforme. This septum when viewed laterally is seen to 

 be perforated by numerous vertical slits, which give its processes a 



