ME SO THE LI A L S TR UC TURES. 



10$ 



break down, placing the coeloms of the two sides in free com- 

 munication. In front a part of this ventral mesentery persists, 

 binding the liver to the anterior abdominal wall, and in many 

 ichthyopsida carrying the sub-intestinal vein to that organ. 

 Another portion, known as the small omentum (or gastro-hepatic) 

 and the duodeno-hepatic omentum extends from the dorsal 

 surface of the liver to the stomach and duodenum (Fig. 1 1 3). 

 The dorsal mesentery is usually far more complete. 1 In it 

 are recognized various regions, named according ^o the organs 

 which they support, mesogaster, mesentery proper, mesocolon, 



FIG. 114. Three stages in the development of the alimentary canal and the 

 mesenteries of man, after Toldt and Hertwig. a, appendix vermiformis ; ao, aorta; 

 , bile duct; c, caecum ; co, colon; </, duodenum; go, great omentum; me, meso- 

 colon ; me, mesentery ; nig, mesogaster ; p, pancreas ; r, rectum ; s, stomach ; si, 

 small intestine ; s/>, spleen ; tc, transverse colon ; v, vitelline duct. The arrow 

 points to the opening of the omentum. 



mesorectum, etc. It is attached to the dorsal wall in a straight 

 line, and in those vertebrates with a straight alimentary canal 

 the mesentery is a plane membrane, but with increasing con- 

 volution of the alimentary canal, the membrane becomes corre- 

 sp< iclingly plaited. Besides this complication, the mesenteries 

 can form secondary unions with the body wall, or with the 



1 In Pctromyzon (cyclostome) it has entirely disappeared, except a few shreds in the 

 rectal region. 



