Chap, xvi.] THE ABDOMINAL PARIETES. 267 



mount up on to the abdomen through this interval, and 

 will then be limited by the deeper layer of the fascia. 

 It will not be able to pass down into the thigh on 

 account of the attachments of the fascia, nor, for a like 

 reason, will it tend to pass over the middle line. In 

 the same way emphysematous collections following 

 injuries to the chest, when beneath the deeper layer 

 of the fascia, receive a check at the groin, and lipomata 

 also that grow beneath the membrane tend to be limited 

 by the middle line and that of Poupart's ligament. 



The anterior abdominal parietes vary in thick- 

 ness in different subjects. In cases of emaciation the 

 outlines of some of the viscera may be readily made 

 out or even seen through the thinned wall. In some 

 cases of chronic intestinal obstruction the outlines 

 of the distended intestine are visible, and their move- 

 ments can be watched. The relative thickness of the 

 abdominal wall in various subjects depends rather 

 upon the amount of the subcutaneous fat than upon 

 the thickness of the muscles. This muscular boundary 

 affords an admirable protection to the viscera within. 

 By contracting the abdominal muscles the front of the 

 belly can be made as hard as a board, and in acute 

 peritonitis this contraction can sometimes be seen to 

 produce a remarkable degree of rigidity. 



A blow upon the abdomen when the muscles are 

 iirmly contracted will probably do 110 injury to the 

 viscera unless the violence be extreme. The rigid 

 muscular wall acts with the efficacy of a dense india- 

 rubber plate. It may be bruised or torn, but it will 

 itself receive the main shock of the contusion. 



The probable effect on the contained viscera of 

 a blow upon the abdomen will depend upon many 

 factors ; but, so far as the walls themselves are con- 

 cerned, the effect greatly depends upon whether the 

 blow was anticipated or not, and upon the extent of 

 the padding of fat that is furnished to the parietes. 



