282 THE ANATOMY OF THE HORSE. 



adapted without stretching to the varj'ing length of the organ. They 

 emit numerous branches to the cavernous and spongy portions of the 

 penis, and terminate in the glans. 



Suspensory Ligaments of the penis (Plate 46). These are two fibrous 

 bands, right and left, which are attached superiorly to the tendon of 

 origin of the gracilis, and below to the cavernous body of the penis. 



Directions. — The penis may now be freed as far as its posterior 

 extremity, and its surface cleaned of vessels, nerves, and connective- 

 tissue. On one side the erector penis muscle should be removed, to lay 

 bare the cms and expose the artery of the corpus cavernosum. 



The Artery of the Corpus Cavernosum (Plate 46). This is a branch 

 d|f the obturator artery, detached after the emergence of that artery 

 from the obturator foramen. It passes backwards on the lower face of 

 the ischium, and perforates the crus penis. It gives off as a collateral 

 branch the posterior dorsal artery of the penis. 



The Penis (Plates 46 and 47) is the male organ of copulation. It 

 begins at the ischial arch, where it is attached by its crura to the ischial 

 tuberosities; and it terminates anteriorly in a free enlargement — the 

 glans. It may be said to consist of a posterior fixed portion, and an 

 anterior portion which is free and protrusible. The former portion 

 extends from the ischial arch to the scrotum; the latter, when the 

 organ is non-erect, is lodged in the prepuce, but during erection the 

 prepuce becomes obliterated, and this part of the penis then projects 

 freely in front of the scrotum. 



The penis is compounded of three longitudinal and parallel columns, 

 viz., two corpora cavernosa and a single corpus sp)ongiosmn. From the 

 relationship of these to one another, the penis has been happily com- 

 pared to a double-bai-relled gun, the barrels being represented by the 

 corpora cavernosa, and the ramrod by the corpus spongiosum. 



The Corpora Cavernosa. Each corpus cavernosum begins at the 

 tuber ischii, to whose inferior ridge (inferior ischiatic spine) it is firmly 

 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. 44). 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 pai't 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 



