| OCR Text |
Show 1896.] INTESTINAL TRACT OP BIRDS. 141 described frequently, were marked by the attachment of a spiral valve. But the rectal part of the intestine, that supplied by the Fig. 4. Struthio camelus ; intestinal tract, x, short-circuiting vessel cut across. posterior mesenteric vein, is expanded into an enormous coil swung at the circumference of a semicircular expansion of its mesentery. Only in Chauna and in the Eagles and Petrels have I found the slightest trace of a convergent resemblance to this feature, but in the latter the subsidiary rectal loops, although supplied by the rectal vessel, lie above the caeca. I have not yet had an opportunity of dissecting a Rhea or an Apteryx1. It is plain that, so far as degree of divergence of type in the alimentary canal goes, the Ratites deserve their accepted place at the bottom of the avian scale. CARINAT.E. COLYMBIFORMES. In these (Podiceps not examined) (fig. 5, p. 142) the duodenal loop is straight and normal. The circular loop is pulled out into a series of minor loops that are arranged almost symmetrically round the middle mesenteric vein. The yolk-sac vestige lies in front of the middle point of the series. The last loop of the circular system 1 [In a Rhea americana which I have more recently examined the gut was intermediate in form between those of Casuarius and Struthio. The anterior portion resembled Casuarius; the rectum had an expansion recalling that in the Ostrich, but much less strongly marked.-P. C. M., March 1896.] |
