Transversi perintei muscles ( Ischio-peri-i N neat ).—This pair of small muscles extends in a direction nearly parallel to the ante rior border of the anal region ; each arises from the inside of the tuber ischii, passes inwards, forwards, and downwards to join its fellow in the median line of the perinaum, where it is also partially attached to the cuta neous sphincter of the anus, and to the acce leratores urina muscles, or in the female to the constrictor vagina. These muscles are very unequal in appearance in different subjects ; in some they are feeble and indistinct, in others very strong, and sometimes divided into two on one or both sides, the additional or minor muscle being superior and anterior. In the female these muscles are often found more dis tinct than in the male, but even here much variety exists ; in many subjects they appear to be simply composed of some of the anterior and partially detached fibres of the middle portions of the levatores ani muscles. The transversi perinai muscles form the bases of the two lateral triangular regions contained in the anterior or urethral perinaum, and one of them, the left, is necessarily divided in the lateral operation for lithotomy ; they are surrounded by much adipose matter ; two arte ries, both branches of the internal pudic, take a course parallel to them, — viz., the super ficial transverse perinwal, and the deep trans verse, or the artery of the bulb. These muscles are enveloped between the layers of the perinaeal fascia. The superficial layer, which is continu ous with the Ischio-rectal, covers them in their course forwards to. the urethral muscles, and the deep layer, or the triangular ligament of the .urethra, which is continuous with the ex ternal or Ischiatic layer or obturator fascia, lies between them and the pelvis. These muscles, therefore, will have the effect of making tense the different perinaal aponeuroses, and thus they can support, strengthen, and compress generally the parts in the perinaum ; they can also compress, and thus assist in clearing the orifice of the anus, at the same time that they draw back and raise this part, somewhat in the same manner as the levatores ani muscles. According to some anatomists these muscles are considered as dilators of the bulb of the urethra, as well as of the vagina ; but it is more than doubtful whether they can exert any such action. When these muscles are divided, the base of the deep perinccal fascia, or triangular ligament of the urethra, is exposed. This will be observed to have some influence in main taining the rectum and anus in their situation ; its posterior border, being attached to the levatores ani muscles, and to the bulb of the urethra, serves to maintain a close connection between these parts, which is still further ef fected by the interlacement of the muscles of the anus with those which cover the bulb.
(See PERIN/EUM.) Levatores ani (sous-pubio-coccygien). —This pair of broad, thin, flat, and nearly square muscles form a septum somewhat broader above than below, between the pelvis and perinaum, which, together with the aponeu roses covering its upper and lower surfaces, and with the coccygeal muscles and the trian gular ligament of the urethra, completely in tercepts all communication between these two regions except through the natural passages for the urethra, vagina, and rectum. Although these muscles are described as two, there ap pears no good reason for the division, for the fibres of opposite sides have a common in sertion, partly into the circumference of the rectum and partly into a middle cellulo-ten dinous raphe before and behind that intestine. It appears more correct to consider these muscles as one circular muscular septum extended across and within the lower opening of the pelvis, concave towards this cavity, and convex to wards the perinaaum. The fibres attached by their circumference to the interior of the pelvis, and converging thence towards the median line of the perinaum, are inserted into and around the rectum ; in fact the muscle resembles the diaphragm in form, in the circumference being its origin or fixed attachment, and the central portion being its insertion, also in its being perforated for the transmission of certain parts ; the analogy only fails in the absence of a central tendon, and in the fibres being prin cipally inserted into the parts passing through it. The fact, however, of there being an inter
ruption in the origin of this muscle in the middle line both before and behind, in which respect again there is a resemblance to the sternal and vertebral deficiences in the dia phragm, is the cause of its being described as consisting of a right and left muscle, which dis tinction, it should be observed, is only an artificial one, for during life the fibres of both sides act together, and in all respects constitute but a single muscle.
The origin of the levator ani muscle may be exposed by tearing the peritonaum from the parietes of the pelvis, together with a con siderable quantity of loose cellulo-adipose membrane. The recto-vesical layer of the pel vic fascia should then be divided near to the neck and sides of the bladder, and carefully raised towards the wall of the pelvis. The muscle will then be seen to arise on each side by three attachments, which, however, form one continuous semicircular line extending from the pubis to the spine of the Ischium ; its anterior portion is attached to the back part of the pubis, a little above its arch, and imme diately below the anterior vesical ligaments by short aponeurotic fibres commencing - a little distance from the symphysis, and extending outwards as far as the notch in the thyroid hole ; its second or middle attachment is to a strong tendinous arch, which extends from the pubis to the spine of the Ischium, and which is formed at the separation or junction of the pelvic fascia into its superior or recto vesical layer, and its inferior or perinaal layer ; its third or posterior attachment is to the spinous process of the ischium. All the fibres pass downwards and towards the median line to their insertion ; the inferior border of this muscle is shorter but thicker than the superior. The fibres of the first, or pupal portion, des cend a little obliquely backwards on each side of the prostate gland and membranous portion of the urethra, and converging beneath the latter are inserted in common between the bulb and the fore-part of the rectum into the central point of the perinmum ; these portions in their descent present a well-defined edge inwards or towards the median line. The middle, or aponeurotic portion, is broad and thin above, the vesical fascia adhering so closely to it as to render its separation difficult. As it descends it increases in thickness, expands close to the rectum, and is inserted into the coats of that intestine, intermingling with its longitudinal, fibres, and with the sphincter ani ; in the female it is intimately attached to the vagina also. The posterior or Ischiatic portion passes al most transversely inwards, and is inserted into the coccyx, and into the cellulo-tendinous line which extends from the latter to the rectum ; some fleshy fibres are continuous from one muscle to the other. This portion of the le vator ani is more aponeurotic than the pre ceding, and its posterior border is connected to the Ischio-coccygwus muscle. The external or inferior surface of this muscle is inclined down wards, and is more or less related to the obtu rator and ischio-rectal fasciae, to the gluteus maximus and transverse perinxal muscles and vessels, and to the mass of anal fat. The internal or concave surface looks upwards, and is closely covered by the vesical fascia, below which it is in contact with the rectum, bladder, prostate gland, and urethra, or with the uterus and vagina. This muscle is disposed on the rectum in the same manner in the female as it is in the male; the fibres are also inti mately connected to the vagina.