INTESTINAL TRACT OF MAMMALS. 455 



of a caecum. The hind-gut is relatively short, very wide and strongly marked with 

 longitudinal striae. It shows no trace of division into colon and rectum. The portal 

 system is simple, consisting of a single anterior mesenteric vein curving round Meckel's 

 tract and receiving numerous tributaries, first a duodenal branch and then many 

 branches from the tract. There is a single rather large posterior mesenteric or 

 rectal vein. 



The pattern of the intestinal tract of Manis is of striking, almost reptilian, simplicity. 

 The peculiarities are the loss of the caecum and the longitudinally striped hind-gut. 

 But for these two features and the loss of any special orientation of the anterior 

 mesenteric vein with regard to the yolk-sac diverticulum, the pattern would closely 

 resemble that found in many primitive Birds. There is very little that is distinctively 

 Mammalian about it. 



Order XENARTHRA. 



Family Beadypodidje. Bmdypus infuscatus (fig. 10, p. 456). 



The duodenum forms a distinct loop of rather wide calibre. Meckel's tract is 

 unusually short, occupying only a small portion of the usually circular area of 

 mesentery. It is separated from the wide hind-gut by a vestigial caecum (C), and 

 opposite this there is (C 2) a still smaller vestige of another caecum, showing that these 

 structures were originally paired. The hind-gut is differentiated into a long, wide 

 colon and a shorter, nearly straight rectum. The position of the colon is somewhat 

 unusual, inasmuch as it occupies a considerable part of the mesenterial expanse 

 generally occupied by the posterior portion of Meckel's tract. The mesenterial out- 

 growth from which the greater portion of the gut is suspended is unusually long and 

 narrow. The portal system consists of a main anterior mesenteric vein which distally 

 curves beyond Meckel's tract and drains part of the colon. There is a long and normal 

 posterior mesenteric vessel. 



Family Myemecophagid.£. Tamandua tetradactyla (fig. 11, p. 457). 



In this Anteater there is a loop which may be recognised as the duodenum, although 

 it is not well separated from the proximal portion of Meckel's tract. Meckel's tract is 

 long, thrown into a regular series of minor loops, the whole area occupying the 

 circumference of a nearly complete oval expanse of mesentery. The usual caecum 

 is absent, but on the other side of the gut there is a vestige (C2) of the other 

 member of the primitive pair. The hind-gut is very short and straight and cannot be 

 regarded as divided into colon and rectum. The portal system is simple : an anterior 

 mesenteric vein, with the usual curved configuration, drains the duodenum and the 

 whole range of Meckel's tract, and there is a well-marked posterior mesenteric vein. 



