840 



SURGICAL ANATOMY OF THE PERINEUM. 



round the inferior border of the Glutaeus Maximus, and are distributed to the 

 integument in this region. 



Fig. 455. Dissection of Perineum and Ischio-Bectal Region. 



The External Sphincter is a thin flat plane of muscular fibres, elliptical in 

 shape, and intimately adherent to the integument surrounding the margin of 

 the anus. It measures about three or four inches in length, from its anterior 

 to its posterior extremity, being about an inch in breadth, opposite the anus. 

 It arises from the tip of the coccyx, by a narrow tendinous band ; and from the 

 superficial fascia in front of that bone ; and is inserted into the tendinous centre 

 of the perineum, joining with the Transversus Perinei, the Levator Ani, and the 

 Accelerator U rinse. Like other Sphincter muscles, it consists of two planes of 

 muscular fibre, which surround the margin of the anus, and join in a commis- 

 sure before and behind. 



Relations. By its superficial surface, with the integument ; by its deep surface 

 it is in contact with the Internal Sphincter ; and is separated from the Levator 

 Ani by loose areolar tissue. 



The Sphincter Ani is a voluntary muscle, supplied by the hasmorrhoidal 

 branch of the fourth sacral nerve. This muscle is divided in the operation for 

 fistula in ano ; and also in some cases of fissure of the rectum, especially if 

 attended with much pain -or spasm. The object of its division is to keep the 

 parts at rest and in contact during the healing process. 



The Internal Sphincter is a muscular ring, about half an inch in breadth, which 

 surrounds the lower extremity of the rectum, about an inch from the margin 

 of the anus. This muscle is about two lines in thickness, and is formed by an 

 aggregation of the involuntary circular fibres of the intestine. It is paler in 

 color, and less coarse in texture, than the External Sphincter. 



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

 rosity 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 upwards, 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 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 Coccygeus 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 

 perinea! fascia : and behind, by the margin of the Glutaeus Maximus, and the 

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

 substance, which explains the frequency with which abscesses in the neighbor- 

 hood of the rectum burrow to a considerable depth. 



