THE PERITONEUM. 



967 



right iliac fossa at the caecum, then upward, across, downward, and into the sig- 

 moid flexure and rectum. This surrounds the coils of the small intestines. 



Liver 



A. gastro-epi- 

 pluica dextrd 



A. gaslrchepi- 

 ploica sinistra 



PUF Omentum majui 



Small intestine 

 FIG. 584. Position of abdominal organs in a state of moderate distention. (Joessel.) 



The other structures not evident without dissection or manipulation can be 

 located by aid of Figs. 582, 583. The organs there are all spaced and so are 

 not in their exact positions. 



It is customary to study the peritoneum before taking up the separate viscera. 

 This membrane has quite a reputation. Whenever in Human Anatomy any- 

 thing is difficult or obscure, one should leave the complex adult form and study 

 the more primitive simple type of the embryo or new-born ; if that be not wholly 

 satisfactory, go to the lower animals (Comparative Anatomy), while the ambi- 

 tious student investigates even fossil animals (Palaeontology). It is meant by 

 this that the medical student should first study something of the development of 

 the peritoneum before opening the abdominal cavity and destroying important 

 structures. 



Some Essential Facts in the Development of the Peritoneum. 



In the early development of the alimentary canal, before the twelfth day in 

 the human embryo, all three germ-layers push forward, are folded over, and pro- 

 duce the head and the anterior part of the fore-gut. This is blind at the front 

 end, and the mouth is developed later by an invagination from the exterior. The 

 middle part of the future alimentary tract, mid-gut, is in free communication for 

 some time with the blastodermic vesicle which is later called the yolk-sac. The 

 approximation of the body-walls at the umbilicus gradually pinches the yolk-stalk 

 off into the vitelline duct, so the sac finally lies wholly outside the body of the 



