212 



DB. P. CHALMERS MITCHELL ON THE 



The carnivorous forms are on the average the larger, and the carnivorous shortening 

 of the :;ut is in consequence disguised by the relative increase in length associated with 

 size. The general features of the group are a tendency for the duodenum to be irregular, 

 eiilar<;ed. very long, or spirally twisted ; for Meckel's tract to exhibit thi-ee definite minor 

 loops anterior to a median loop bearing a Meckel's diverticulum, and. posteriorly to that, 

 first one or two irregular loops and then a supra-duodenal loop and at least one supra- 

 cu'cal kink drained by the rectal vein : the caeca are always vestigial and the rectum 

 short and straight. The departures from this common type are — first, the irregularities 

 in tlie fish-eaters ; second, a progressive tendency for the lengthening of ^Meckel's tract 



Fig. 34. 



Intestinal Trnot of P((iidwn haliaetvs. Letterins: as before. 



in the axial line with consequent obliteration of one or more of the otlier minor loops, 

 and, in the most apocentric ca.ses, with a spiral folding of the tract; third, Serpentarim 

 shows distad of the first three loops of Meckel's tract a circular expansion of the mesentery 

 bearing a number of minor loops, and this condition leads naturally to the condition in 

 ('ailiartcs, where the circular expansion involves the second and third of the definite 

 loops on the proximal side of Meckel's tract. Attempts have been made to show a more 

 intimate relation between the Cathartte and some of the Ciconiiform birds than between 

 those and other Falconiformes ; there is no ground for such a conclusion in the structure 

 of the intestinal tract. Still less ground is there for attempting to place ia intimate 



