ANUS. 



179 



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 perinaeum ; 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-coccygaeus 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 glutaeus 

 maxim us and transverse perinaeal 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. 



The action of the levator ani muscles is 

 two-fold, and not confined to the mere ele- 

 vation of the anus, as its name would im- 

 ply. First, they act as a moveable floor to 

 the abdomen and pelvis, which can antago- 

 nize the diaphragm ; these two fleshy planes 

 being opposed to each other, can, by a slight 

 action of one or both, materially alter the 

 perpendicular axis of the abdomen, which 

 extends between them. This axis is at its great- 

 est length during the state of expiration, and is 

 most diminished when both these muscles are 

 forcibly contracting. The levatores ani, how- 

 ever, have less influence in effecting this change 

 than the diaphragm ; they serve chiefly to 

 support the lower region of the pelvis and the 

 several viscera this cavity contains against the 

 combined protruding forces of the diaphragm 

 and abdominal muscles in violent exertions of 

 the body, or in forcible efforts of respiration, 

 or in the evacuation of the contents of the rec- 

 tum and bladder ; and, secondly, they not 

 only raise, but dilate the anus, by drawing out 

 its circumference so as to overcome the sphinc- 

 ters ; at the same time they compress and 

 assist in emptying the rectum, particularly the 

 dilated pouch, which is a little above the anus; 

 they also resist the prolapsus of the mucous 

 coat of the intestine, and raise it after it has 

 been to a certain extent protruded by the action 

 of the abdominal muscles. They raise and draw 

 forward the coccvx after it has been forced back 



by abdominal pressure in parturition, or in the 

 ordinary evacuation of the bowels, and further, 

 by raising and compressing the trigone of the 

 bladder, they assist in expelling its contents, 

 and for the same reason they can also empty the 

 vesiculae seminales of their fluid. The anterior 

 portions of these muscles are intimately con- 

 nected to the membranous part of the urethra, 

 and are variously modified in different indi- 

 viduals and in different animals; we consider 

 those muscular fasciculi which have been de- 

 scribed differently by anatomical writers under 

 different names, compressores urethrae, &c., as 

 parts of or appendages to these muscles : these 

 urethral portions of the levatores ani can cer- 

 tainly compress the membranous part of the 

 urethra and empty its canal ; they can even 

 interrupt or suddenly stop the stream of urine, 

 and thus they may occasionally aid the neck of 

 the bladder in retaining the contents of that 

 organ. 



The Ischio-cocct/gcei muscles are situated at 

 the posterior inferior part of the pelvis ; they 

 are thin, flat, and triangular, composed of a mix- 

 ture of fleshy and tendinous fibres. The apex 

 or origin of each is attached to the spine of the 

 Ischium, and its base is inserted into all the side 

 of the coccyx, and a small portion of the 

 sacrum ; they are partly covered by the great 

 sciatic ligaments. The superior and posterior 

 border is connected to the lesser sciatic liga- 

 ment, and the anterior border is in part con- 

 tinuous with the levator ani muscle ; the an- 

 terior or pelvic surface is connected to the 

 rectum and the surrounding adipose substance. 

 This pair of muscles appear as a prolongation 

 of the levatores ani, and are of use in com- 

 pleting the inferior boundary of the pelvis; 

 they thus support the rectum and the pelvic 

 viscera, and they also serve to retain the coccyx 

 and restore it to its situation when protruded by 

 the diaphragm and abdominal muscles in the pro- 

 cess of parturition, and in the act of defalcation, 

 or when drawn too much forward by the levatores 

 ani muscles. If the several muscles in this 

 region be now partially removed on one side, 

 the lower extremity of the rectum will become 

 more distinct, and will be found surrounded by 

 a quantity of loose, fatty, cellular tissue, sepa- 

 rating it from the surrounding muscles and 

 bones; this contains many nervous filaments 

 and numerous bloodvessels, particularly veins. 

 (See INTESTINAL CANAL.) Anteriorly in the 

 male subject a small triangular space, the 

 bulbo-rectal hollow, will now become distinct ; 

 this is situated between the anus and mem- 

 branous portion of the urethra ; the base of it 

 is at the skin of the perinaeum ; the apex at 

 the prostate : to the last the rectum will be 

 seen rather intimately connected. The bulb and 

 the membranous portion of the urethra bound 

 this space in front, and the rectum behind. 

 (See PERINEUM and URETHRA.) 



Rectum. In addition to the several muscles 

 which have now been severally noticed, and 

 which thus serve not only to retain and support 

 the rectum and anus, but which even enter into 

 the structure of the former, we have further to 

 consider the parts more immediately composing- 



