1202 SURGICAL ANATOMY OF THE PERINEUM. 



In this region, and connected with the lower end of the rectum, are four muscles : 

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

 Levator ani. 



These muscles have been already described (see pages 458 and 459). 



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

 tuberosity of the ischium on each side. 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 sui-face 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 and deep perineal fasciae; 

 and behind, by the margin of the Gluteus maximus and the great sacro-sciatic liga- 

 ment. 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 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 (Fig. 374). Cross- 

 ing the space transversely, about its centre are the inferior haemorrhoidal vessels 

 and nerves, branches of the internal pudic ; they are distributed to the integu- 

 ment 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 haemorrhage 

 when divided in the operation of lithotomy or of fistula in ano. At the back part 

 of this space 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 PERINEUM 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 

 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 peringeum 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. 767, 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 



