THE MUSCLES AND FASCIAE OF THE RECTUM AND ANUS. 1675 



pouches opening upward. They are situated in the anal canal at the upper part 

 of the internal sphincter. The mucous membrane of the rectum is thrown into a 

 series of longitudinal folds. These are easily effaceable, although some are continu- 

 ous with the columns of Morgagni. 



The submucous coat is lax, allowing the mucous membrane to be readily dis- 

 placed, but at the lower end of the anal canal the latter is firmly attached to the 

 muscles. 



The muscular coat of the rectum is thicker than that of the colon, reaching to 

 2 mm. The thickening is greatest in the layer of the circular fibres. The longitu- 

 dinal ones, although forming a continuous layer, are for the most part collected 

 front and back into the two bands already mentioned, of which the posterior is the 

 larger and the more concerned in bridging over the folds. The internal sphincter is 

 but an hypertrophy of the circular muscles, while the external sphincter is a muscle 

 of the perineum. It has been thought advisable to describe here together the 

 muscles and some of the fasciae of the rectum and anus, including some that are 

 largely extrinsic. 



THE MUSCLES AND FASCIA OF THE RECTUM AND ANUS. 



Thelevator ani(Figs. 1423, 1424) arises from the back of the body of thepubes, 

 about midway between the upper and lower border, very close to the middle line, 

 and thence, from the ' ' white line' ' formed by the splitting of the pelvic fascia, as 

 far as the spine of the ischium. The anterior fibres from the pubic bone pass below 

 the prostate, some going to its capsule, as a strong muscular bundle to the central 



FIG. 



1423. 



Bulbo-cavernosus 



Ischio-cavernosus 



Trans, perinei 

 superf. 



Triangular lig- 

 ament, inf. layer 



- Perineal centre 



_.;. Tuberosity of 

 ischium 



Anus 



Obturator fascia 



External 



sphincter 

 Levator ani 



-7- Glutens 



maximus (cut) 



Greater sacro- 

 sciatic ligament 



Coccyx 



Muscles of pelvic floor and perineum from below. 



point of the perineum and the front and sides of the rectum, in which some of them 

 end. The remainder of this set passes with the fibres from the white line to the 

 side of the coccyx and to a fibrous band (ligamentam anococcygeum) running from it 

 to the anus. This latter part of the muscle is thinner and more transversely placed 

 than the former. In the female the pubic portion sends some fibres to the vagina 

 and some around it to the central point of the perineum. The fibres, for the most 



