47 6 APPLIED ANATOMY. 



urethra may be too small to permit the entrance of the finger and a blunt guide is 

 introduced, along which forceps may be passed to extract any foreign body. In 

 Cock' s operation for retention of urine the index finger of one hand is introduced 

 through the rectum and its tip placed at the apex of the prostate. A straight knife is 

 then inserted 2.5 cm. (i in.) in front of the anus and pushed up and inward into the 

 urethra, being guided by the finger in the rectum. (For removal of enlarged 

 prostate see page 450. ) 



Lateral Lithotomy. The incision is begun to the left of the median line 3 

 cm. (i^ in.) in front of the anus and carried outward and back midway between 

 the anus and tuberosity of the ischium. The knife is pushed steadily on until it enters 

 the groove in the Staff and thence backward into the bladder. The artery to the 

 bulb is to be avoided by not going more than 3 cm. in front of the anus. The rec- 

 tum is to be avoided by having it empty, by hooking the staff in the urethra well up 

 to the pubic arch, thus drawing the urethra up, and by inclining the knife obliquely 

 outward. The internal pudic artery is to be avoided by keeping away from the ramus 

 of the ischium. Too free an incision of the prostate is bad because urinary infiltration 

 is liable to occur in the pelvic fascia, also an accessory pudic artery, which if present 

 may run along the side of the prostate, may thus be wounded. Usually the bleeding 

 is slight and comes from the division of the superficial transverse perineal and branches 

 of the inferior hemorrhoidal arteries and the prostatic plexus of veins. (For Perineal 

 Prostatectomy see page 450 and Seminal Vesicles page 452.) 



Anal Triangle and Ischiorectal Region. The anal triangle is made by the 

 superficial transverse perineal muscles forming its base and the tip of the coccyx its 

 apex. It contains the anal canal with the ischiorectal fossae on each side. 



The ischiorectal fossa is wedge-shaped, its base, extending between the tuber- 

 osity of the ischium and the anus, is about 2.5 cm. (i in.) in breadth, and its apex 

 extends up 5 to 7.5 cm. (2 to 3 in. ), to the junction of the levator ani and internal 

 obturator muscles. Its inner wall is formed by the levator ani and coccygeus muscles 

 and its outer wall by the obturator internus muscle. Its deepest extreme posterior 

 portion constitutes the posterior recess. This communicates superficially, beneath the 

 coccygeal attachment of the external sphincter, with the fossa of the opposite side 

 (see Fig. 475, page 473). 



The anterior recess (pubic, Waldeyer) runs forward between the prostate gland 

 internally and the ischiopubic ramus externally ; the deep and superficial transverse 

 perinei muscles and the deep layer of the triangular ligament are superficial to it. 



The internal pudic vessels and pudic nerve lie on the internal obturator muscle 

 and ramus of the ischium in a fibrous canal formed by the obturator fascia. It is 

 called AlcocK s cauat and is 4 cm. (i/^ in.) above the tuberosity. 



The inferior hemorrhoidal vessels and nerves enter the ischiorectal fossa at its 

 posterior and outer side and run on the surface of the levator ani muscle toward the 

 anus. The superficial perineal vessels and nerves enter the fossa anteriorly and imme- 

 diately pierce the posterior edge of the superficial perineal ( Colics' s) fascia to supply 

 the structures between it and the superficial layer of the triangular ligament. 



Practical Application. The principal affection of the ischiorectal fossa is abscess. 

 This is probably started by violence and infected from the rectum. It commonly 

 tends to point through the skin or open into the rectum. On account of its ten- 

 dency to burrow it is to be opened early. This is done by making an incision of 

 ample size through the skin and then opening the abscess by blunt dissection in 

 order to empty all pockets. Bleeding is usually slight because the vessels lie deep 

 and escape being wounded. Should the abscess not break externally it may do so 

 internally. If superficial it pierces the anal canal between the external and internal 

 sphincters and makes an opening at about the white line. If it is very deep it may 

 open into the ampulla of the rectum above the internal sphincter (see page 443). 

 It is more common for pus to burrow down into the ischiorectal space through the 

 levator ani than it is for it to burrow up from the ischiorectal fossa (Tuttle). There- 

 fore in extensive ischiorectal abscesses communicating with the interior of the pelvis 

 one should look for the origin of the trouble above. An abscess on one side is liable 

 to be followed by one on the other and pus quite commonly crosses the median line 

 posterior to the anus. 



