444 



THE MUSCULATURE 



and into the median raphe on the free surface of the bulb. By its contraction the 

 bulbo-cavernosus forces semen or urine from the bulbous part of the urethra. 



The superficial transverse muscle of the perineum (figs. 392, 394) arises on 

 each side from the ascending ramus of the ischium and is inserted into the central 

 tendon of the perineum. It is frequently weakly developed. It acts with the 

 deep transverse perineal muscle in fixing the perineum and thus offering support 

 for the action of other muscles. 



In the female (fig. 392) the ischio-cavernosus does not differ markedly from that 

 in the male although usually it is smaller. The superficial transverse muscles are, 

 on the other hand, usually relatively better developed. The central tendon of 

 the perineum is likewise usually better developed in women and is more elastic, a 

 characteristic of value in childbirth. 



The chief difference in the musculature in the two sexes is found in the 

 hulho-cavernosus (fig. 392) . This, in the female, arises from the back of the clitoris, 

 the corpus cavernosum and the trigone. It covers the outer side of the bulb of 

 the vestibule and the gland of Bartholin. It is inserted into the central tendon of 

 the perineum. The chief function of the pair of muscles is to constrict the vagina. 



The external genital muscles are covered by a deep layer of the tela subcutanea, 



Fig. 399. — Diagram to show the Fascia op the Pelvis in Section. (After Hell.) 



Levator am 



Endo- 

 pelvic 

 fascia 



Splincter ani externus 



Rectum 



Ischio-rectal fossa 



Colles' fascia, which is firmly fused with the two layers of the urogenital trigone 

 at the anal margin of the latter. 



MORPHOLOGICAL REMARKS 



While the shoulder-girdle and the muscles which extend from this and from the trunk to the 

 upper extremity are superficially placed with respect to the trunk, and do not interrupt the trunk 

 musculature the reverse is true of the hip-girdle and the musculature of the lower extremity. 

 The hip-pirdle is firmly united to the spinal column at the sacrum. The muscles which arise 

 from the trunk and are attached to the lower limbs are few in number compared with those of 

 the upper extremity and, unlike the latter, are deeply placed. Thus the psoas major muscle 

 (fig. 400) arises on "each side of the lumbar region of the spinal column at the back of the ab- 

 dominal cavity and is inserted into the femur and the piriformis (fig. 406) arises from the front 

 of the sacrum at the back of the pelvic cavity and is inserted into the great trochanter of the 

 femur. The skeleton and musculature of the lower extremity, furthermore, markedly inter- 

 fere with the continuity of the trunk musculature which in the lower vertebrates and in the hu- 

 man eml)ryo may be followed continuously to the caudal end. The interruption is much less 

 marked behind than in front. The intrinsic dorsal spiiuil musculature extends well down over 

 the l)ack of the sacrum, but on the back of the lower end of the sacrum and on the back of the 

 coccyx there is found merely the inconstant sacro-coccygeus posterior. Of the ventro-lateral 

 musculature the musculature of the abflominal wall, as is indicated by its innervation, is de- 

 rived from the lower thoracic and the first one or two lumbar myotomes; thequadratus lum- 

 borum, at the back of the abdominal cavity (fig. 40G), from the first three or four lumbar myo- 



