146 TOPOGRAPHIC AND APPLIED ANATOMY. 



PLATE 20. 

 The female pelvic outlet as seen from without. From a Leipzig model from nature (His). 



below the pyriformis there are only narrow spaces, the suprapyrijorm and infrapyriform foramina, 

 through which important vessels and nerves make their exit from the pelvis. The lesser sacro- 

 sciatic foramen gives passage to the obturator internus muscle, which arises from the inner 

 surface of the obturator membrane and its immediate vicinity and inserts into the great tro- 

 chanter. In the upper and inner portion of the obturator membrane there is a small opening, 

 the obturator canal, through which the obturator artery and nerve leave the pelvis and through 

 which the obturator vein enters it. 



At the pelvic outlet there is stretched a funnel-shaped musculo-tendinous plate, the dia- 

 phragma pelvis. The chief portion of the pelvic diaphragm is formed by the levator ani muscle. 

 It arises from the white line (arcus tendineus) in the obturator fascia, which extends from the 

 posterior surface of the horizontal ramus of the pubis to the spine of the ischium. In the male 

 the muscle is inserted into the rectum and into the prostate; in the female, into the rectum 

 and into the vagina. The closure of the inferior pelvic aperture is completed anteriorly by the 

 musculo-tendinous plate of the diaphragma urogenitale (trigonum urogenitale), triangular liga- 

 ment, which is stretched across the pubic arch. In the male the urogenital diaphragm gives 

 passage to the membranous portion of the urethra; the muscular tissue surrounding the urethra 

 in this situation is known as the compressor urethrse muscle. This septum is also perforated 

 by the deep veins of the penis which enter the corpora cavernosa. In the female it gives passage 

 to the vagina as well as to the urethra. 



The pelvic diaphragm divides the larger superior from the smaller inferior portion of the 

 pelvis. The former is the direct continuation of the abdominal cavity and, as it contains the 

 pelvic viscera, it may be called the visceral portion of the pelvic space. The abdominal viscera are 

 also found in this deepest portion of the peritoneal space, but they are kept out of the pelvis 

 to a greater or less extent by the amount of space required by the pelvic viscera. The extra- 

 visceral portion of the pelvic space is situated below the pelvic diaphragm and between it and 

 the inferior portion of the lateral pelvic wall (the ischium and the overlying obturator internus 

 muscle) ; it is filled with fat and forms the ischiorectal fossas. 



In the extravisceral portion of the pelvic space the terminal portions of the viscera passing 

 through the pelvic diaphragm are surrounded by the clamp-like musculature which renders 

 possible the opening and the closing of the particular visceral canal. 



The external sphincter ani muscle surrounds the terminal portion of the rectum in a circular 

 manner. The superficial fibers run from before backward to insert into the tip of the coccyx. 

 Anteriorly the fibers are continuous with the bulbocavernosus muscle in the male and with the 

 constrictor cunni * muscle in the female. [According to Cunningham, the most superficial fibers 

 of the external sphincter ani decussate in front of and behind the anus; the deepest fibers are 

 arranged in a circular direction around the canal, while between these the bulk of the muscular 

 fibers are attached posteriorly to the coccyx, anteriorly to the central tendon of the perineum, 

 reducing the empty canal to an anteroposterior slit on horizontal section. ED.] The bulbo- 



* The sphincter vaginae. 



