176 



DE. P. CHALMEKS MITCHELL ON THE 



this simple condition. Cuvier (5) divides this median portion into an "Anse moyenne" 

 extending from the duodenum to Meckel's diverticulum, and an ''■ Anse coUque," from 

 the diverticulum to the insertion of the ciBca. The examination of a larger number of 

 types, however, shows that althougli the remains of the yolk-sac when |)resent give a 

 point of orientation, still there is not a natural pomt of division between the loops 

 at the insertion of the yolk rudiment, which, indeed, most frequently lies at the 

 summit of a minor loop. Moreover, the adjective "colic" rightly belongs to a lower 



Fig-. 1. 



Intestinal Tract of Palamedca cornuta. From^). to jm'. is the Duodenum ; from p.ti. to ex., the insertion of the cajca, 

 is Meckel's Tract ; from c.c. to d. is the Large Intestine, here convoluted in its anterior portion, G *. 



/>.!'., portal vein ; n.m.v., anterior mesenteric or duodennl vein; ;«.»(. v., middle mesenteric vein"; p.m.r., posterior 

 mesenteric or rectal vein : .r, " bridging " factor of duodenal vein from caeca : ^, recurrent factor of middle 

 mesenteric vein; p., pylorus; m., Meckel's diverticulum; cZ., cloaca; n.n.. nerves entering mesentery; v.n., 

 " visceral nerve," ganglionated chain of the autonomic nervous system. 



portion of the gut, as the colon of mammalian anatomy, fi'om which the name was 

 taken, is not the portion on which Meckel's diverticulum may be found. It is worth 

 noting, however, that very often a change in the colour of the gut, denoting a phase in 

 the digestive processes, begins just distal to the diverticulum. Meckel's tract, in the 



* Since the large intestine is, with few exceptions, short in birds and but rarely differentiated into anything 

 comparable to a colon, it will be simider to refer lo it in this Memoir as j-ecfum. 



