94 PHYSIOLOGY AT THE FAEM. 



The external wall of the abdominal cavity that is, its in- 

 ferior wall may be marked out into zones and regions, as in 

 the human body; namely, an anterior, middle, and posterior 

 zone ; and each of these zones into three regions. Thus the 

 anterior zone consists of the epigastric region, in the middle, 

 flanked on each side by the right and left hypochondriac 

 region ; the middle zone has, in the middle, the umbilical re- 

 gion, flanked on each side by the right and left lumbar region ; 

 and the posterior zone has the hypogastric region in the middle, 

 flanked right and left by an iliac region. Three regions of the 

 pelvis may be added to these namely, the pubic region, and 

 on each side a right and left inguinal region (fig. 5). 



The lining membrane of the abdominal cavity in the ox has 

 the same general character as in man and the higher animals. 

 It is a serous membrane, known widely throughout the verte- 

 brated orders as the peritoneum. In the ox, as in similar 

 animals, it is a shut sac, so disposed that the surface of 

 attachment by which it adheres to the several organs con- 

 tained in the abdomen is the outer side of the sac. The 

 inner surface of the sac is absolutely empty, unless that it 

 contains as much moisture as damps the finger when it is 

 touched. During perfect health every part of the inner sur- 

 face of the peritoneal sac is in close contact with some other 

 part of the same surface. This inner surface is, however, a 

 secreting surface, commonly, as said above, giving forth no 

 more fluid than is sufficient to damp the finger. Yet in mor- 

 bid states this secretion may increase to an immense extent, so 

 as to constitute dropsy of the abdomen that is, dropsy in the 

 peritoneal cavity. Thus the sac of the peritoneum is all but 

 empty in health ; but, being capable of allowing the accumula- 

 tion of fluid, when the secretion augments, or the ordinary 

 rate of absorption fails, it is one of those cavities termed 

 by physiologists a potential cavity. 



