ABDOMEN. 245 



This is an explanation of the fact you can demonstrate on the cadaver : that 

 the small intestine is almost completely surrounded by the ascending transverse 

 and descending parts of the colon. Show this on your work. 



32. Formation of greater and lesser peritoneal cavities. 



In figure 172 you have the primitive peritoneal partition dividing the abdom- 

 inal cavity into a right and a left half. In front of the stomach you see the gastro- 

 hepatic omentum ; behind the stomach the mesentery, which now takes the 

 specific name meso-gaster. You see the initial end of the small intestine (duo- 

 denum), and below this the remainder of the small intestine and all the large intes- 

 tine, attached by a common mesentery ; that peritonium, however, which corres- 

 ponds to the colon is called meso-colon, and that which corresponds to the small 

 intestine is called mesentery. Can you now distinguish the three meso-structures ? 

 Can you remember that each has two layers, between which are located the mesen- 

 teric arteries and other contents ? Can you remember that the attached margin 

 of this meso-gut now extends from the floor of the pelvis to the diaphragm, in 

 the mid-line ? Can you remember that the intestinal margin of the meso-gut 

 must become longer, in proportion to the growth of the intestine, large and 

 small ? Now you are on the left of this partition. Thus far the space on the right 

 is as great as that on the left. The arrow in figure 173 is represented as simply 

 coming through an artificial opening, to aid you in remembering the space on the 

 other side of the partition. Now imagine you took hold of the partition, the 

 meso-gaster, and pulled toward you in the direction of the dotted line. Would 

 you not, by continued pulling, produce a bagging-out on your side of the parti- 

 tion, and a consequent depression or bagging-in on the other side ? Can you 

 imagine, now, if you pulled long enough, the beginning of the depression or sac 

 on the other side must become smaller and smaller? The hole on the other side 

 would admit you to this little sac thus formed by your pulling. In anatomy the 

 name of this hole is the foramen of Winslow. It 'leads to the sac you have just 

 formed. This sac is the lesser cavity of the peritoneum ; all the space outside 

 of this is the greater cavity of the peritoneum. 



33. What parts of the abdominal viscera, in the adult, have lost their peritoneal 

 covering by pressure atrophy, as referred to in a preceding paragrapJi / 



No two cases are exactly alike in this regard. Still, the following represents 

 a general average, as you will meet these cases in the dissecting-room : (i) The 

 posterior part of the descending colon rests on the posterior wall of the abdomen, 

 consequently there is adhesion, with loss of the specific epithelial element. (2) The 

 ascending colon, the second and third parts of the duodenum, the colic and 

 duodenal elbows to be presently explained, rest on the peritoneum, partially in- 

 vesting the right kidney, and here is peritoneal loss. The second part of the 

 rectum is adherent to the anterior surface of the sacrum, and here is peritoneal 

 loss. Each case is a law unto itself, in a measure ; but the student with an ink- 

 ling of the developmental principles, as given in the foregoing, and as elaborated 

 in Morris, can soon acquire a facility in locating on his dissections, those peri- 

 toneal ruins, whose presence forms one of the mainstays for the receptacular part 

 of the alimentary canal, whose absence belongs to the rarest of rare developmental 

 freaks. 



34. Does rotation occur in every case ? 



Faulty rotation, and even failure to rotate, may occur. One interesting case, 

 found recently by the author, showed the caecum and the entire colon on the left 

 side, the small intestine in or near the right iliac fossa. 



35. Are any special organs developed from the alimentary canal .' 



The liver and pancreas are developed from the duodenum ; the former grows 

 into the mesentery in front of the stomach, the latter into the posterior meso-gaster. 

 You will see their ducts open in common into the second part of the duodenum. 



