SPHINCTER ANI LEVATOR ANI. 199 



The perpendicular portion* described by Mr. Wilson, arises by 

 two tendinous points from the inner surface of the arch of the pubis, 

 on each side of, and close to the symphysis. The tendinous origins 

 soon become muscular, and descend perpendicularly, to be inserted 

 into the upper fasciculus of the transverse portion of the muscle ; so 

 that it is not a distinct muscle surrounding the membranous portion 

 of the urethra, and supporting it as in a sling, as described by Mr. 

 Wilson, but merely an upper origin of the transverse muscle. 



The compressor urethras may be considered either as two sym- 

 metrical muscles meeting at the raphe, or as a single muscle: I have 

 adopted the latter course in the above description, as appearing to 

 me the more consistent with the general connexions of the muscle, 

 _and with i1$ actions. 



The Sphincter ani is a thin and elliptical plane of muscle closely 

 adherent to the integument, and surrounding the opening of the 

 anus. It arises posteriorly in the superficial fascia around the 

 coccyx, and by a fibrous raphe from the apex of that bone ; and is 

 inserted anteriorly into the tendinous centre of the perineum, and 

 into the raphe' of the integument, nearly as far forwards as the com- 

 mencement of the scrotum. 



Relations. By its superficial surface with the integument. By 

 its deep surface with the internal sphincter, the levator ani, the cel- 

 lular tissue and fat in the ischio-rectal fossa, and in front with the 

 superficial perineal fascia. 



The Sphincter ani internus is a muscular ring embracing the 

 extremity of the intestine, and formed by an aggregation of the cir- 

 cular muscular fibres of the rectum. 



Part of the levator ani may be seen during the dissection of the 

 anal portion of the perineum by removing the fat which surrounds 

 the termination of the rectum in the ischio-rectal fossa. But to study 

 the entire muscle, a lateral section* of the pelvis must be made by 

 sawing through the pubis a little to one side of the symphysis, sepa- 

 rating the bones behind at the sac"ro-iliac symphysis, and turning 

 down the bladder and rectum. The pelvic fascia is then to be care- 

 fully raised, beginning at the base of the bladder and proceeding 

 upwards, until the whole extent of the muscle be exposed. 



The Levator ani is a thin plane of muscular fibres, situated on 

 each side of the pelvis. It arises from the inner surface of the os 

 pubis, from the spine of the ischium, and between those points from 

 the angle of division between the obturator and the pelvic fascia. 

 Its fibres descend to be inserted into the extremity of the coccyx 

 into a fibrous raphe in front of that bone, into the lower part of the 

 rectum, base of the bladder, and prostate gland. 



* Mr. Tyrrell, who has made many careful dissections of the muscles of the perineum, 

 has not observed this portion of the muscle ; he considers Wilson's muscle (with some 

 other anatomists) to be the anterior fibres of the levator ani, not uniting beneath the 

 urethra as described by Mr. Wilson ; but inserted into a portion of the pelvic fascia 

 situated between the prostate gland and rectum, the recto-vesical fascia. 



