II. Perinea! Aponeuroses.
These extend vertically, from the body and symphysis of the pubes, to an imaginary line drawn between the two ischiatic tuberosities. They are limited transversely, by the ischio-pubic rami to which they unite.
They are placed one under the other, forming true compartments by the union of their posterior edges at the level of the imaginary bis-ischiatic line. They are crossed by the urethra and vagina, but not by the rectum, which lies below.
Proceeding from behind forwards, and from within outwards these aponeuroses may be divided into: a. Deep Perineal Aponeurosis.—It is attached above to the lower sur face of the triangular ligament, laterally to the internal face of the ischio pubic rami, near the sub-pubic canal, and to the internal face of the ischi atic tuberosities. Crossed by the urethra and vagina, it adheres to this canal, behind the constrictor or sphincter vaginae. Its posterior edge, on a level with the bi-ischiatic line, curves from above downward, and from in front backward, in order to unite with the two other perineal aponeu roses.
b. Median Aponeurosis.—It is attached to the anterior face of the body of the pubes behind the clitoris, then to the internal surface of the ischio pubic rami. Like the deep perineal aponeurosis, it is crossed by the urethra and vagina, and seems to turn on itself to sheathe this canal and attach itself there, enveloping the constrictor or sphincter vagina. Its posterior edge blends with the posterior edge of the deep aponeurosis. (See Figs. 26 and 27.) c. Superficial Aponeurosis.—Above, it is inserted on the anterior face of the body of the pubes, covering the root of the clitoris, and blending with the abdominal aponeurosis, laterally on the external surface of the ischio-pubic rami. There it turns to envelop the sphincter vaginae, and the roots of the clitoris. Behind it blends, by its posterior edge, which curves from below upwards, and from in front backwards, with the edges of the middle and deep aponeuroses.
Thus traversed by the urethra and the vagina, the edges of these aponeu roses penetrate deep into the labia majors, and are inserted in the deep layers of skin of these labia at the point where the skin is united to the internal membrane of the vagina.
Above is the skin, which is pierced by three openings, the anal, the vaginal and the urethral.
Muscles of the Perinmum.
These are: the levator ani, the ischio-coccygeus, the sphincter ani, the constrictor vagina?, the transversus perinei, and the ischio-cavernous.
Pajot describes together the levator ani and the ischio-coccygeal.
The Levator Ani and Ischio-coccygeus.—A double symmetrical muscle, it forms a layer stretched above the superior strait. We have to consider the superior concave surface, the inferior convex surface, and the cir cum ference.
In front, it is inserted on the internal surface of the body of the pubes, very close to the symphysis, on the posterior surface of the horizontal ramus of the pubes, on a fibrous arch, the pubo-sciatic, which spans the space between the inferior edge of the pubes and the sciatic spine, on the edge and apex of the sciatic spine, and on the anterior face of the lesser sciatic ligament. From these various attachments its fibres radiate in ward to a fibrous raplie which extends from the coccyx to the rectum, and are attached to the lateral walls of the rectum, to the raphe between the rectum and the vagina, to the lateral edges of the vagina, and to the lateral walls of the bladder.
Those fibres which pass from the sciatic spine, and from the sciatic ligament, to the coccyx, form the ischio-coccygeal muscle. This muscle thus forms the posterior fasciculus of the levator ani.
Immediately below the superior pelvic aponeurosis the levator ani is covered on its inferior or convex surface, at least anteriorly, by an aponeu rotic layer, the inferior aponeurosis of the levator ani. Budin, in a recent work, calls attention to a contraction of the fibres of this muscle which Hildebrandt had already mentioned, and which may become, in certain cases, a true cause of tedious labor.