FASCIA 



445 



tomes. Beyond here there is an interruption until we come to the musculature of the pelvic 

 outlet which, in part, may be looked upon as modified trunk musculature belonging to the last 

 three sacral myotomes. The intervening region is "cut out" for the reception of the base of the 

 lower extremity. 



It is of interest to note that more and more of the ventro-lateral wall of the trunk is "cut 

 out" as the mid-ventral line is approached. Thus while the quadratus lumborum behind 

 represents spinal segments as far caudal as the third or fourth lumbar, the rectus abdominis 

 in front represents segments merely as far caudal as the twelfth thoracic. Similarly while the 



Fig. 400. — Sagittal Section through the Urogenital Trigone and Ischio-rectal Fossa 

 TO the Left of the Middle Line. (Diagrammatic.) 



Piriformis 



Obturator fascia 



Subperitoneal tissue 

 Fascia transversalis 



Os pubis 

 Obturator internus 



Fascia lata of thigh 

 Muscles of thigh 



Sacrum 



Nerves 



Sacro-tuberous ligament 



Sacro-spinous ligament 



Gluteus maximus 

 Levator ani with its fasciae 



Ischio-rectal fossa 



Deep perineal interspace 



with sphincter urethras, 



etc. 

 Superficial fascia of 



urogenital trigone 



Superficial perineal interspace 

 with muscles of penis 



coccygeus at the back part of the pelvic outlet represents the third and fourth sacral segments, 

 the levator ani at the front represents chiefly the fourth. 



The musculature which in the tailed mammals is used to move the tail as well as to wall off 

 the pelvic cavity and close rectal and urogenital openings, in man is modified wholly for the latter 

 functions. It constitutes the pelvic diaphragm. 



The musculature of the urogenital diaphragm of the external genitalia and anus in man is 

 differentiated from the primitive sphincter of the cloaca. 



FASCIiE 



The tela subcutanea in the male perineal region contains many bundles of smooth muscle 

 fibres continuous with and similar to the dartos of the scrotum (corrugator cutis ani). At the 

 sides where it passes over the lower margin of the gluteus maximus it contains a large amount of 

 fat, but in the dorsal region over the coccyx and sacrum, as in the mid-perineal region, the fat 

 is limited in amount. In the labia majora of the female perineu^n there is much fat in the tela 

 aubcutanea. 



The ischio-rectal fossa (figs. 401, 402) is bounded laterally by the obturator internus muscle 

 and fascia, the tuberosity of the ischium and the ischio-pubic ramus, medially by the levator ani 

 and coccygeus muscles and fasciae, ventrally by the dorsal aspect of the urogenital trigone and 

 dorsaUy by the gluteus maximus muscle. An anterior recess extends forward well toward the 

 body of the pubis between the levator ani, the ischio-pubic ramus and the urogenital trigone. 

 A posterior recess may likewise be traced backward covered by the lower edge of the gluteus 

 maximus (figs. 400, 401). The fossa is filled with loose fatty tissue continuous with that of 

 the tela subcutanea. Through it pass the hajmorrhoidal, and long and short perineal branches 

 of the pudic artery and nerve. The main trunks of these vessels and nerves lie in a special 

 fascial compartment (Alcock's canal) in the lateral wall (fig. 401). 



The external genital organs are cover'^d by a special deep layer of the tela subcutanea, the 

 superficial perineal (Colles') fascia (fig. 402). This is attached on each side to the lower margm 

 of the ischio-pubic ramus and to the ischial tuberosity. At the posterior margin of the superficial 

 transverse perineal muscle it fuses with the two fascial layers of the trigone. It is adherent to 

 the central tendon of the perineum and to the raphe of the bulb. Anteriorly it is contmuous 

 with the deep layer of the tela subcutanea covering the scrotum, the penis, and the lower part 

 of the abdominal wall. In rupture of the urethra urine is prevented, by the attachments of the 

 tela, from getting further back than the posterior edge of the trigone, but anteriorly it may 

 extend to the surface of the abdomen. Here it may extend upward for a considerable distance, 

 but it is kept from the thighs by the attachment of the deep layer of the tela subcutajiea (Scarpa s 

 fascia) to the inguinal ligament. Beneath the superficial perineal fascia are found the crura of 



