THE ANAL MUSCLES 191 



the great sacrosciatic ligament and bounds the ischiorectal 

 fossa externally. Near its upper margin it gives off the anal or 

 ischiorectal fascia, which covers the levator ani externally and 

 bounds the ischiorectal fossa internally. 



The fascia of the pyriformis is continued back from the 

 obturator in front of the pyriformis muscle and sacral plexus. 



The rectovesical fascia is attached in front to the back of 

 the pubis, and laterally separates from the obturator fascia 

 along a curved line from the upper part of the obturator fora- 

 men to the ischial spine; this is the posterior part of the white 

 line which extends from the pubis to the ischial spine. The 

 fascia, covering the upper surface of the levator ani muscle, 

 passes to the prostate gland, bladder, rectum, and from side 

 to side across the median line. The part to the prostate and 

 neck of the bladder from the pubis consists largely of involun- 

 tary muscular fibers, the anterior true ligaments of the bladder, 

 or puboprostatic ligaments; outside them are the lateral true 

 ligaments, and the part going to the rectum is the ligament 

 of the rectum. The anterior part of the fascia meets the bladder 

 along its junction with the prostate, and divides into two 

 layers; the upper (ascending) unites with the muscular coat 

 of the bladder, and is attached just outside the vesiculae semi- 

 nales; the inferior layer (descending) forms the sheath of the 

 prostate, and at its apex is continued into the upper layer of 

 the triangular ligament; it also passes between the bladder 

 and rectum and forms the front of the sheath of the latter. 

 The vagina receives the rectovesical fascia in a manner similar 

 to the prostate. 



THE MUSCLES OF THE PERINEUM IN THE MALE 



Two groups anal and genitourinary, comprising a super- 

 ficial and a deep set in each. 



I. The Anal Muscles 



The internal or circular sphincter is a thick ring of unstriped 

 muscle continuous with the circular fibers of the rectum. 



The external sphincter, one inch in depth, is elliptical, attached 

 by a small tendon to the coccyx, encloses the anus, and superficial 



