MESOTHELIAL STRUCTURES. 



105 



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.^ In it 

 are recognized various regions, named according to 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 ; 

 b, bile duct; ^, caecum ; co, colon; d, duodenum; go, great omentum; ?«c, meso- 

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

 small intestine ; sp, 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- 

 spondingly plaited. Besides this complication, the mesenteries 

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



1 In Petromyzon. (cydostorae) it has entirely disappeared, except d few shreds in the 

 rectal region. 



