176 



DE. P. CHALMEES 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 colique," from 

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

 types, however, shows that although the remains of the yolk-sac when present give a 

 point of orientation, still there is not a natural point 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 Palamedea cornuta. From p. to p.v. is the Duodenum ; from p.v. to c.c., the insertion of the caeca, 

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



p.v., portal vein ; a.m.v., anterior mesenteric or duodenal vein ; m.m.v., middle mesenteric rein'; p.m.v., posterior 

 mesenteric or rectal vein ; ,r, " bridging " factor of duodenal vein from cseca ; R, recurrent factor of middle 

 mesenteric vein ; p., pylorus ; m., Meckel's diverticulum ; el., 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, from 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 oi' the gut, denoting a phase in 

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



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

 comparable to a colon, it will be simpler to refer to it in this Memoir as rectum. 



