1064 SURGICAL ANATOMY OF THE PERINJEUM. 



muscles : the Corrugator cutis ani ; the two Sphincters, External and Internal ; 

 and the Levator ani. 



These muscles have been already described (see page 368). 



The ischio-rectal fossa is situated between the end of the rectum and the 

 tuberosity of the ischium. It is triangular in shape ; its base, directed to the 

 surface of the body, is formed by the integument of the ischio-rectal region ; its 

 apex, directed upward, corresponds to the point of division of the obturator fascia 

 and the thin membrane given off from it, which covers the outer surface of the 

 Levator ani (ischio-rectal or anal fascia). Its dimensions are about an inch in 

 breadth at the base and about two inches in depth, being deeper behind than in 

 front. It is bounded, internally, by the Sphincter ani, Levator ani, and Coc- 

 cygeus muscles; externally, by the tuberosity of the ischium and the obturator 

 fascia, which covers the inner surface of the Obturator internus muscle ; in front, 

 it is limited by the line of junction of the superficial fascia with the base of the 

 triangular ligament ; and behind, by the margin of the Gluteus maximus and the 

 great sacrq-sciatic ligament. This space is filled with a large mass of adipose 

 tissue, which explains the frequency with which abscesses in the neighborhood of 

 the rectum burrow to a considerable depth. 



If the subject has been injected, on placing the finger on the outer wall of this 

 fossa the internal pudic artery, with its accompanying veins and the two divisions 

 of the nerve, will be felt about an inch and a half above the margin of the ischiatic 

 tuberosity, but approaching nearer the surface as they pass forward along the inner 

 margin of the pubic arch. These structures are enclosed in a sheath (canal of 

 Alcock) formed by the obturator fascia, the pudic nerve lying below the artery 

 and the dorsal nerve of the penis above it (Fig. 315). Crossing the space trans- 

 versely, about its centre are the inferior hemorrhoidal vessels and nerves, which 

 are distributed to the integument of the anus and to the muscles of the lower end 

 of the rectum. These vessels are occasionally of large size, and may give rise to 

 troublesome hemorrhage when divided in the operation of lithotomy or in that for 

 fistula in ano. At the back part of this space, near the coccyx, may be seen a 

 branch of the fourth sacral nerve, and at the fore part of the space the superficial 

 perineal vessels and nerves can be seen for a short distance. 



THE PERINJEUM PROPER IN THE MALE. 



The perineal space is of a triangular form ; its deep boundaries are limited, 

 laterally, by the rami of the pubic bones and ischia, meeting in front at the pubic 

 arch ; behind, by an imaginary transverse line extending between the anterior 

 parts of the tuberosities of the ischia. The lateral boundaries are, in the adult, 

 from three inches to three inches and a half in length, and the base from two to 

 three inches and a half in breadth, the average extent of the space being two 

 inches and three-quarters. 



The variations in the diameter of this space are of extreme interest in connection with the 

 operation of lithotomy and the extraction of a stone from the cavity of the bladder. In those 

 cases where the tuberosities of the ischia are near together it would be necessary to make the 

 incisions in the lateral operation of lithotomy less oblique than if the tuberosities were widely 

 separated, and the perineal space consequently wider. The perinaeum is subdivided by the 

 median raphe into 'two equal parts. Of these, the left is the one in which the operation of 

 lithotomy is performed. 



In the middle line the perinaeum is convex, and corresponds to the bulb of the 

 urethra. The skin covering it is of a dark color, thin, freely movable upon the 

 subjacent parts, and covered with sharp crisp hairs, which should be removed 

 before the dissection of the part is commenced. In front of the anus a prominent 

 line commences, the raphe, continuous in front with the raphe of the scrotum. 



Upon removing the skin and superficial structures from this region, in the 

 manner shown in Fig. 590, a plane of fascia will be exposed, covering in the 

 triangular space and stretching across from one ischio-pubic ramus to the other. 

 This is the deep layer of the superficial fascia or fascia of Colles. It has already 



