424 MYOLOGY 



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, which it supports as in a sling, it has been described as a distinct 

 muscle, under the name of Levator prostatse. In the female the anterior fibers of 

 the Levator ani descend upon the side of the vagina. 



The Levator ani may be divided into iliococcygeal and pubococcygeal parts. 



The Iliococcygeus arises from the ischial spine and from the posterior part of the tendinous 

 arch of the pelvic fascia, and is attached to the coccyx and anococcygeal raph6; it is usually thin, 

 and may fail entirely, or be largely replaced by fibrous tissue. An accessory slip at its posterior 

 part is sometimes named the Iliosacralis. The Pubococcygeus arises from the back of the pubis 

 and from the anterior part of the obturator fascia, and "is directed backward almost horizontally 

 along the side of the anal canal toward the coccyx and sacrum, to which it finds attachment. 

 Between the termination of the vertebral column and the anus, the two Pubococcygei muscles 

 come together and form a thick, fibromuscular layer lying on the raphe formed by the Iliococcygei" 

 (Peter Thompson). The greater part of this muscle is inserted into the coccyx and into the last 

 one or two pieces of the sacrum. This insertion into the vertebral column is, however, not 

 admitted by all observers. The fibers which form a sling for the rectum are named the Pubo- 

 rectalis or Sphincter recti. They arise from the lower part of the symphysis pubis, and from the 

 superior fascia of the urogenital diaphragm. They meet with the corresponding fibers of the 

 opposite side around the lower part of the rectum, and form for it a strong sling. 



Nerve Supply. The Levator ani is supplied by a branch from the fourth sacral nerve and 

 by a branch which is sometimes derived from the perineal, sometimes from the inferior hemor- 

 rhoidal division of the pudendal nerve. 



The Coccygeus (Fig. 404) is situated behind the preceding. It is a triangular 

 plane of muscular and tendinous fibers, arising by its apex from the spine of the 

 ischium and sacrospinous ligament, and inserted by its base into the margin of the 

 coccyx and into the side of the lowest piece of the sacrum. It assists the Levator 

 ani and Piriformis in closing in the back part of the outlet of the pelvis. 



Nerve Supply. The Coccygeus is supplied by a branch from the fourth and fifth sacral nerves. 



Actions. The Levatores ani constrict the lower end of the rectum and vagina. They elevate 

 and invert the lower end of the rectum after it has been protruded and everted during the expul- 

 sion of the feces. They are also muscles of forced expiration. The Coccygei pull forward and 

 support the coccyx, after it has been pressed backward during defecation or parturition. The 

 Levatores ani and Coccygei together form a muscular diaphragm which supports the pelvic 

 viscera. 



VI. THE MUSCLES AND FASCUE OF THE PERINEUM. 



The perineum corresponds to the outlet of the pelvis. Its deep boundaries 

 are in front, the pubic arch and the arcuate ligament of the pubis; behind, the tip 

 of the coccyx; and on either side the inferior rami of the pubis and ischium, and the 

 sacrotuberous ligament. The space is somewhat lozenge-shaped and is limited 

 on the surface of the body by the scrotum in front, by the buttocks behind, and 

 laterally by the medial side of the thigh. A line drawn transversely across in 

 front of the ischial tuberosities divides the space into two portions. The pos- 

 terior contains the termination of the anal canal and is known as the anal region; 

 the anterior, which contains the external urogenital organs, is termed the urogenital 

 region. 



The muscles of the perineum may therefore be divided into two groups: 



1. Those of the anal region. 



2. Those of the urogenital region: A, In the male; B, In the female. 



1. The Muscles of the Anal Region. 

 Corrugator cutis ani. Sphincter ani externus. Sphincter ani internus. 



The Superficial Fascia. The superficial fascia is very thick, areolar in texture, 

 and contains much fat in its meshes. On either side a pad of fatty tissue extends 



