OF THE PERINEUM. 369 



extremity of the rectum for about an inch, its inferior border being contiguous 

 to, but quite separate from, the External sphincter. This muscle is about two 

 lines in thickness, and is formed by an aggregation of the involuntary circular 

 fibres of the intestine. It is paler in color and less coarse in texture than the 

 External sphincter. 



Actions. Its action is entirely involuntary. It helps the External sphincter 

 to occlude the anal aperture. 



The Levator ani (Fig. 222) is a broad, thin muscle, situated on ea^h side of 

 the pelvis. It is attached to the inner surface of the sides of the true pelvis, and 

 descending, unites with its fellow of the opposite side to form the floor of the 

 pelvic cavity. It supports the viscera in this cavity and surrounds the various 

 structures which pass through it. It arises, in front, from the posterior surface 

 of the body of the os pubis on the outer side of the symphysis; posteriorly, from 

 the inner surface of the spine of the ischium ; and between these two points, from 

 the angle of division between the obturator and recto-vesical layers of the pelvic 

 fascia at their under part. The fibres pass downward to the middle line of the 

 floor of the pelvis, and are inserted, the most posterior into the sides of the apex 

 of the coccyx ; those placed more anteriorly unite with the muscles of the opposite 

 side in a median fibrous raphe, which extends between the coccyx and the margin 

 of the anus. The middle fibres, which form the larger portion of the muscle, are 

 inserted into the side of the rectum, blending with the fibres of the Sphincter 

 muscles ; lastly, the anterior fibres, the longest, descend upon the side of the 

 prostate gland to unite beneath it with the muscle of the opposite side, blending 

 with the fibres of the External sphincter and Transversus perinaei muscles at the 

 central tendinous point of the perinseum. 



The anterior portion is occasionally separated from the rest of the muscle by 

 connective tissue. From this circumstance, as well as from its peculiar relation 

 with the prostate gland, descending by its side, and surrounding it as in a sling, 

 it has been described by Santorini and others as a distinct muscle, under the name 

 of Levator prostatae. In the female, the anterior fibres of the Levator ani descend 

 upon the side of the vagina. 



Relations. By its inner or pelvic surface, with the recto-vesical fascia, which 

 separates it from the viscera of the pelvis and from the peritoneum. By its outer 

 or perineal surface, it forms the inner boundary of the ischio-rectal fossa, and is 

 covered by a thin layer of fascia, the ischio-rectal or anal fascia, given off from the 

 obturator fascia. Its posterior border is free and separated from the Coccygeus 

 musele by a cellular interspace. Its anterior border is separated from the muscle 

 of the opposite side by a triangular space, through which the urethra, and in the 

 female the vagina, passes from the pelvis. 



Nerve-supply. A branch from the anterior division of the fourth sacral nerve 

 and a branch from the pudic nerve, which is sometimes derived from the perineal, 

 sometimes from the inferior haemorrhoidal division. 



Actions. This muscle supports the lower end of the rectum and vagina, and 

 also the bladder during the efforts of expulsion. It elevates and inverts the lower 

 end of the rectum after it has been protruded and everted during the expulsion of 

 the faeces. It is also a muscle of forced expiration. 



The Coccygeus is situated behind and parallel with the preceding. It is a tri- 

 angular plane of muscular and tendinous fibres, arising, by its apex, from the 

 spine of the ischium and lesser sacro-sciatic ligament, and inserted, by its base, 

 into the margin of the coccyx and into the side of the lower piece of the sacrum. 

 It assists the Levator ani and Pyriformis in closing in the back part of the outlet 

 of the pelvis. 



Relations. By its inner or pelvic surface, with the rectum. By its external 

 surface, with the lesser sacro-sciatic ligament. The lower border is in relation 

 with the posterior border of the Levator ani, but separated from it by a cellular 

 interval : its upper border is in relation with the lower border of the Pyriformis, 

 but separated from it by the sciatic and internal pudic vessels and nerve. 

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