678 MUSCLES OF THE PERINEUM. 



fine but dense aponeurosis, forming the immediate cov- 

 ering to the muscles. This, however, is sometimes called 

 the deep fascia, though this latter term, to avoid confusion, 

 has been restricted to another fascia still deeper, the tri- 

 angular ligament , which has been already described. 



The muscles of the perineum are seen on removing the 

 fascia, and are ten in number, the 



Sphincter externus, Transversus perinei, 



Sphincter internus, Coccygeus, 



Erectores penis, Levatores-ani. 

 Acceleratores urinae, 



The sphincter externus, or ani, (Fig. 213,) is a cutane- 

 ous muscle, surrounding the anus, and presenting a flat, 

 thin, pale, and elliptical plane of fibres. It has two fixed 

 points of attachment one to the os-coccygis and recto-coc- 

 cygeal ligament behind, which is called its origin ; the 

 other to the central point of union of the perineal muscles 

 in front, and also to the superficial fascia and raphe, which 

 is the insertion. On surrounding the anus, it expands 

 outward nearly to the tuberosities of the ischia. 



Function. To .-close the anus, and draw the bulb of the 

 urethra back, or the coccyx forward. 



Sphincter internus, or orbicularis. This muscle surrounds 

 the lower portion of the rectum, is in close contact with 

 the mucous membrane, and is regarded simply as a contin- 

 uation and thickening of the circular muscular coat of this 

 intestine. Function. To assist in closing the anus. 



The erector or compressor penis (Fig. 213) arises, fleshy 

 and tendinous, from the inner and anterior surface of the 

 tuber ischii. Its fibres adhere to the rami of the ischium 

 and pubis, and end in a tendinous expansion which is lost 

 or inserted into the fibrous membrane of the corpus caver- 

 nosum or crura penis. This muscle is long and narrow. 



Function. To draw down and compress the penis, and 

 thus aid in its erection by preventing the return of the 

 blood, though its use, by some, is not considered as fully 

 understood. 



