chap, xvi.] POSTERIOR ABDOMINAL PARIETES. 317 



thigh to form the anterior layer of the crural sheath. 

 The iliac fascia encloses the ilio-psoas muscle, the part 

 over the psoas being the thinner. This part is attached 

 on the inner side to the sacrum, and to the spine at 

 points corresponding to the psoas origin. Above, it is 

 attached to the ligamentum arcuatuni internum, and 

 on the outer side to the anterior layer of the lumbar 

 fascia along the outer edge of the psoas. Below, the 

 fascia encloses the iliacus, and is attached to the iliac 

 crest, to the pelvic brim, and to Poupart's ligament, 

 save at that part where the membrane passes beneath 

 the ligament to form the posterior wall of the crural 

 sheath. It follows the ilio-psoas muscle to its insertion, 

 and ends by blending with the fascia lata. 



The arrangement of these fasciae greatly influences 

 the progress and direction of abscess. Thus an abscess 

 beneath the transversalis fascia will be very definitely 

 enclosed. If it progresses backwards it will be stopped 

 at the . outer edge of the psoas muscle. If it spreads 

 downwards it will be arrested by the attachments of 

 the fascia to the iliac crest and to Poupart's ligament, 

 and will be unable to spread (unless the fascia be 

 pierced) into either the pelvis or the thigh. On the 

 inner side it will be checked at the middle line ; and 

 above, although it will meet with no actual resist- 

 ance, it would be indisposed to spread, since its move- 

 ments would be against gravity. Thus, it happens 

 that collections so placed point either just above the 

 iliac crest or Poupart's ligament, or run down along the 

 spermatic cord, and distend the inguinal canal. 



The iliac fascia encloses the ilio-psoas in a very 

 distinct osseo-aponeurotic space. Between the fascia 

 and the muscle (especially its iliac division) there is 

 a good deal of loose connective tissue, and thus every 

 facility is offered for the progress of subfascial abscesses 

 in this region. The osseo-aponeurotic space is practi- 

 cally closed on all sides within the abdomen, and is 



