34 PHYSIOLOGY AT THE FAKM. 



rectum. The gullet, as already mentioned, passes through the 

 chest, to terminate in the stomach after piercing the diaphragm. 

 The lowest division of the great intestine, which, owing to its 

 being nearly straight, is called rectum, passes through the 

 pelvis, following the course of the os sacrum, or rump-bone, 

 to end in the fundament. 



As the inferior and lateral walls of the abdomen are power- 

 ful muscles, as well as the anterior wall formed by the dia- 

 phragm, the wall constituted by the abdominal muscles, rein- 

 forced by a powerful elastic covering, is capable of antagonis- 

 ing that formed by the diaphragm ; while if these several 

 muscular boundaries contract simultaneously, the contents of 

 the abdominal cavity may be strongly compressed. 



It is useful to mark out, by imaginary lines, certain exter- 

 nal regions of the abdomen which correspond more or less 

 exactly to the place of the organs situated within. In the 

 horse, as in mammals generally, the abdomen is marked out by 

 perpendicular lines into three zones an anterior, a middle, 

 and a posterior, as in fig. 5 and each of these three zones is 

 divided by longitudinal horizontal lines into three subordinate 

 regions. The three regions of the anterior zone are the epi- 

 gastric in the middle, and the right and left hypochondriac on 

 either side. The three regions of the middle zone are the 

 umbilical in the middle, and the right and left lumbar re- 

 gion on either side. The three regions of the posterior zone 

 are the hypogastric in the middle, and the right and left iliac 

 region on either side. 



Part of the epigastric region, and of the left hypochondriac 

 region, are occupied by the stomach ; the right hypochondriac 

 region, part of the epigastric region, and even a minute por- 

 tion of the left hypochondriac region, are occupied by the liver. 

 The spleen lies in the left hypochondriac region. The pancreas, 

 or sweetbread, is situated in the epigastric region, lying across 







