56o 



HUMAN ANATOMY. 



geus lying along its posterior margin. Above the upper margin of the latter, and 

 forming the posterior wall of the pelvis, is the pyriformis. Slight intervals occupied 

 by connective tissue usually exist between the coccygeus and the other two muscles, 

 presenting opportunities for pelvic hernias. 



I. Levator Ani (Fig. 551). 



Attachments. — The levator ani arises from the posterior surface of the body of 

 the OS pubis in front, from the spine of the ischium behind, and in the interval between 

 these two points from a thickening of the upper border of the obturator fascia, the 

 white line. From this long line of origin the fibres converge downward and medially 

 to be inserted into the sides and tip of the coccyx, into a tendinous raphe extending 

 in the median line between the tip of the coccyx and the anus, and into the sides of 

 the lower part of the rectum. The fibres from the most anterior portion of the origin 

 pass almost directly backward and downward to reach the sides of the rectum, and 

 between them and the corresponding fibres of the muscle of the opposite side is a 



Fig. 551. 



Pyriformis -| 



Coccygeus 



Ischial spine 



Obturator 

 internus 



White line^ \ 

 Levator ani 



Tip of coccyx 



— Ischial spine 



-—Rectum (cut) 



Obturator inter- 

 nus covered by 

 pelvic fascia 



Urethra (cut) 



Muscular floor of pelvis, viewed from above. 



space, occupied in the male by the lower part of the prostate gland and in the female 

 by the base of the bladder and lower part of the vagina, the fascia endopelvina in 

 this region coming into contact with the upper surface of the superior layer of the 

 triangular ligament of the perineum. 



Nerve-Supply. — The posterior portion of the muscle is supplied by a special 

 branch from the third and fourth sacral nerves, the anterior portion by twigs from the 

 inferior hemorrhoidal branches of the pudic nerve. 



Action. — To bend the coccyx forward and to raise the pelvic floor and viscera. 



Variations. — The levator ani is always a well-developed muscle, although the extent of its 

 attachment to the sides of the coccyx varies inversely to the attachment of the coccygeus to that 

 bone. There i:5 usuaHy to be found a dividing line extending across the muscle on a level with 

 the junction of the superior ramus of the pubis with the ilium and separating those fibres which 

 are inserted into the coccyx and the posterior portion of the fibrous raphe from those which 

 pass to the anterior part of the raphe and the rectum. Each of the portions so separated is sup- 

 plied by a separate nerve, and this, combined with the results of comparative anatomy, seems 

 to show that the posterior portion of the levator is really a muscle quite distinct from the ante- 

 rior portion. It has been termed the m. ilio-coccygeus. Furthermore, it seems probable that 



