THE ABDOMEN 



725 



Transverse Meso<olon • ^ 

 Great Omentum 1 J. 



The mesoduodenum disappears. . ^ , 4. 4.v „„.^„*^,„ 



The mesojejunum and meso-ileum persist and represent the mesentery 



proper. ... . 



The meso-appendix persists as the appendicular mesentery. 



The ascending and descending mesocolon and the iliac mesocolon, as a 



rule, disappear. 



The pelvic mesocolon 

 persists and the mesorec- 

 tum disappears. 



Structure of the Peri- 

 toneum. — The peritoneum 

 is a typical serous mem- 

 brane hke the pleura, the 

 serous portion of the peri- 

 cardium, and the tunica 

 vaginalis. Briefly stated, 

 it consists of a homo- 

 geneous connective-tissue 

 basement membrane, con- 

 taining elastic tissue, and 

 lined with endothelium. 

 Its free surface presents 

 many stomata (especially 

 over the diaphragm) , which 

 communicate with the 

 cavity of the peritoneum 

 and with the lymph-canaU- 

 cular system. 



Development.— The 

 parietal peritoneum is de- 

 veloped from the somatic 

 mesoderm of the somato- 

 pleure of the body -wall. 

 The visceral peritoneum is 



Fig. 310. — Diagram of the Peritoneum in developed from the 

 Early Life (Vertical Section). splanchnic mesoderm of 



the splanehnopleure of the 



S. Stomach; P. Pancreas; D. T>\xoden\JiVa.; primitive intestinal tube. 

 T.C. Transverse Colon ; S.I. Small Intestine. 



Blood-suppIy of the Intestinal Canal. — ^The 



intestinal canal receives its blood-supply from 

 the superior and inferior mesenteric arteries, 

 with the exception of the upper portion of 

 the duodenum, and a portion of the rectum. 



Superior Mesenteric Artery. — ^This vessel 

 springs from the front of the abdominal aorta 

 about \ inch below the coeliac axis. It is at 

 first directed downwards behind the body of 

 the pancreas and the splenic vein. It then 

 passes downwards and forwards in front of 

 the uncinate process of the pancreas and third 

 part of the duodenum, at the lower border of 

 which latter it takes up its position between 

 the two layers of the mesentery proper. The 



vessel then passes downwards near the root p^^ 311.— End o- 

 of the mesentery, its course being slightly thelium of a Serous 

 curved with the convexitv towards the left :Membrane. 



