460 ABDOMEN 



from the pelvic surface of the ischial spine ; the intermediate 

 fibres, constituting the greater part of the muscle, take origin 

 in the angle between the visceral and parietal layers of the 

 pelvic fascia. 



Insertion. The anterior fibres pass downwards and back- 

 wards. A few of them are inserted into the central point of 

 the perineum ; others are inserted into the wall of the anal 

 canal, between the internal and external sphincters ; and some 

 join with the intermediate fibres, which sweep round into the 

 angle between the posterior wall of the rectum and the upper 

 end of the anal canal, where they unite with their fellows of 

 the opposite side and form a strong muscular collar round 

 the gut ; the lower fibres of this group are inserted into the 

 posterior wall of the anal canal between the two sphincters. 

 The posterior fibres pass backwards and medially, and are 

 inserted into the median ano-coccygeal raphe, behind the 

 rectum, and into the side of the lower part of the coccyx. 

 The anterior fibres of the muscles of the opposite sides 

 embrace the lateral surfaces of the prostate as they pass back- 

 wards, and are frequently called the levatores prostates. (Fig. 

 214). As the intermediate and posterior fibres pass to their 

 insertions they support the infero- lateral surfaces of the 

 bladder and the lateral walls of the rectum. When the 

 muscle contracts, as a whole, it tends to elevate the pelvic 

 viscera. The fibres inserted into the wall of the anal canal 

 pull that wall upwards over descending faeces, and there- 

 fore aid defalcation. The fibres which form the collar- 

 like loop round the angle between the rectum and the anal 

 passage will, on contraction, increase that angle, and tend to 

 prevent the passage of the contents of the rectum into the 

 anal passage. 



Mm. Coccygei. The coccygei muscles are two small 

 triangular sheets of muscle which continue the plane of the 

 pelvic diaphragm posterior to the levator ani. Each arises 

 from the pelvic surface of the ischial spine and the adjacent 

 pelvic fascia, and, expanding as it passes medially, it is inserted 

 into the margin of the last piece of the sacrum and the 

 anterior surface of the upper part of the coccyx. Its anterior 

 margin is continuous with the levator ani, and its posterior 

 margin is separated from the lower border of the piriformis 

 by the inferior gluteal and pudendal vessels and the sciatic 

 and pudendal nerves, as they pass out of the pelvis. 



