MUSCLES OF PELVIC OUTLET 



439 



thoracis has also been seen. Small fasciculi may pass to neighbouring structures : the CBsophagus, 

 stomach, liver, mesentery, etc. Muscle fasciculi are frequently found in the central tendon. 



V. MUSCULATURE OF THE PELVIC OUTLET 



In order to understand the musculature of the pelvic outlet it is necessary first 

 to consider briefly the structure of the pelvis. It is bounded laterally and in front 

 by the ilium below the terminal (ilio-pectineal) line, the ischium and the pubis, and 

 by the obturator membrane and the sacro-spinous (small sciatic), sacro-tuberous 

 (great sciatic) and the interpubic ligaments. The pubis, ischium and the obturator 

 membrane are covered bj' the obturator internus muscle (figs. 392, 401) which here 

 takes its origin and which converges toward and passes through the lesser sciatic 

 notch on its way to its insertion on the great trochanter of the femur. The piri- 

 formis muscle (figs. 393, 396), which arises from the sides of the pelvic surface of 



Fig. 394. — The Male Perineum. (Modified from Hirschfeld and Leveille.) 



Bulbo-cavernosus 



Superficial layer of uro-genital trigone 

 Ischio-cavernosus 



Posterior femoral cutaneous nerve 



Perineal nerve 

 Inferior haemorrhoidal nerve 

 Cutaneous branch of fotuth sacral 



Gluteus mazimus 

 Tuberosity of ischium 

 Sacro-tuberous ligament 

 Levator ani 

 Superficial transversus perinei 



Sphincter ani 



the sacrum, from the posterior border of the great sciatic notch and the neighbour- 

 ing part of the sacro-tuberous (great sciatic) ligament nearly fills up the great 

 sciatic notch on its way to its insertion on the great trochanter. The walls of the 

 pelvis are thus padded by muscles which belong to the limb. The muscles are 

 covered by fascia best developed over the obturator internus muscle as the 

 obturator fascia. The gluteus maximus muscle (figs. 392, 394, 400, 401), which 

 arises from the back of the ilium, the sacrum, and the coccyx, and is inserted into 

 the femur and the fascia of the thigh overlaps to some extent the sacro-tuberous 

 Hgament, and in the standing position the tuberosity of the ischium so that its 

 lower margin forms an accessory boundary to the pelvic outlet. 



