DISSECTION OF THE ABDOMEN. 299 



iind these rest upon a layer of vascular connective-tissue. The object 

 of the membrane is to facilitate the movements of the different ab- 

 dominal organs on each other and on the walls of the cavity, and 

 especially to facilitate the vermicular or peristaltic movements of the 

 intestines. For this purpose the surface of the membrane is kept moist 

 by a sparing amount of serous fluid, which gives to the membrane its 

 glistening aspect. 



To trace the exact disposition of the peritoneum in the horse is very 

 difficult, in consequence of the unwieldy character of the intestines. 

 When the student has the opportunity he should examine the mem- 

 brane in a foal, in which the different organs can be manipulated with 

 ease. 



The parietal and visceral peritoneum, as has already been stated, 

 form portions of one great sac, and the various abdominal viscera are 

 external to this sac. The sac of the peritoneum, it must be observed, 

 encloses not an actual, but merely a potential, cavity ; the inner surface 

 of every portion of the sac being in contact with the same surface of 

 another portion. To facilitate the understanding of this, let the student 

 imagine the cavity of the abdomen (including the pelvis) as having its 

 natural form, but deprived of all its contents, and completely lined by 

 peritoneum, which, for simplicity's sake, he may suppose to be elastic. 

 The continuity of the membrane, and the fact that it formed a close 

 sac would then be apparent. Now let him imagine a simple tube of 

 intestine extending between this membrane and the spinal column, that 

 is, outside the serous sac. Conceive next this tube of intestine let 

 gradually down, until it extends through the cavity about its centre. 

 In this descent the intestine would first surround itself with peritoneum ; 

 and then, as it sank farther, it would stretch the membrane so as to 

 form a kind of sling passing upwards to the point from which it started. 

 The membrane would now have lost its simplicity, for it woidd have a 

 parietal division continuing to line the abdominal walls, and a visceral 

 portion surrounding the tube of intestine. Moreover, these two portions 

 would be continuous with each other along the sling-like portion sus- 

 pending the tube. Lastly, imagine the tube of intestine to grow and 

 branch, so as to completely fill up the abdominal cavity, and 

 obliterate the space between the parietal and visceral peritoneum. This, 

 of course, would not destroy the continuity of the serous sac, although it 

 would complicate it so that its continuity would be difiicvilt to trace. 



All the organs, then, that actually project into the abdominal cavity 

 get a more or less complete investment of visceral peritoneum ; and, in 

 the case of each organ, this visceral covering is traceable on to a neigh- 

 bourino- organ, or on to the walls of the abdomen. Where organs are 

 contiguous to each other or to the abdominal parietes, the peritoneum 

 may pass directly from the one organ to another or to the abdominal 



