Henry Gray (18251861). Anatomy of the Human Body. 1918.
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 prostatæ. 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 raphé; 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 raphé 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 Puborectalis 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 hemorrhoidal 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 expulsion 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.
1F. The Muscles and Fasciæ of the Perineum
The perineum corresponds to the outlet of the pelvis. Its deep boundaries arein 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 posterior 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