CO MR. F. E. BEDDARU OX THE 



distinctive in the negative sense are not universal. There are 

 whole orders of Mammals, e. g. Oarnivora, Marsupials, Primates, 

 Edentata, in which the colon has no permanent loops, while in 

 many birds, e. g. Gallinaceous birds, certain Picopasseres, the 

 small intestine has no fixed loops. In addition to this very 

 important difference, there appear to me to be two other distin- 

 g-uishing featvires in the alimentary systems of the two orders, 

 which are perhaps equally important and are certainly more 

 regularly met with. In all Mammals above those few forms 

 (e. g. certain carnivorous Marsupials, certain Edentata * ), which 

 have so far retained the Reptilian characters of gut, the whole 

 intestine is rotated upon itself and the rotation is fixed and the 

 change of position of the various sections of the gut retained by 

 the ligamentum cavo-duodenale which moors the end of the 

 duodenal loop to the colon, mesocolon, or median dorsal body-wall 

 on or near the postcaval vein. This ligament correlated with 

 the said rotation is universal among the higher and present in 

 most of the lower Mammals, In Birds, on the contrary, there is 

 no such tract of mesentery fixing the duodenum to the colon. So 

 far, in fact, the bird's intestine has retained the primitive Reptilian 

 condition. The bird's intestine, however, usually has what the 

 mammal's intestine has not, a duodeno-ileie ligament. This doubt- 

 less is the ijhysiologieal equivalent of the duodeno-colic ligament 

 (as Mitchell t has pointed out), in so far as it serves to anchor the 

 perhaips otherwise inconveniently long and coiled small intestine. 

 It may also perhaps be argued from this that a short intestine 

 (<?. g, many Picopasseres) is shown to be a secondary state of affairs, 

 from the very fact that it is in those birds provided with a duodeno- 

 ileic ligament, which may not be a mechanical necessity. For 

 the existence of the ligament in question may be due to mecha- 

 nical needs in an ancestor with a long small intestine. In any 

 case, the morphological fact is to be noted and it constitutes a real 

 difference between the Mammalian and Avian gut. 



In very nearly all birds whose intestinal tract is at or above 

 the level of that of the Cassowary, the end of the small intestine + 

 is attached by a mesentery of vaiying degree of development to 

 the duodenum. This, without any further specialisation, is the first 

 stage in the evolution of the gut from its simple archaic form. 

 This stage characterises the hypothetical Gallinaceous birds in 

 which it is universally present and quite similar in alL 



This simple stage, which we may term Stage A, is also found in 

 other groups, but it does not occur in all the members of a.ny 

 other group as it does in the case of the Gallinaceous birds. 

 Among the Struthious birds, for example, we have it in the 

 Cassowaries, Ostrich, and Apteryx §, whose intestinal tracts are 



* For a general sui-vey, see Klaiatsclij Morpli, Jabrb.- xviii. 1892, and myself in 

 P. Z. S. 1908, p. 568 &G, 



t Trims. Z. S, xvii. p, 524, 



[J; The chief exception known tO' me is fnniislied by Fratercula arctica, the 

 remarkable characters of tlie intestine of which bird I have already coanmentcd 

 upon {supra, p. 78). 



§ The condition of Rhea requires perhaps further study. 



