OCR Text |
Show 158 ON THE INTESTINAL TRACT OF BIRDS. [Jan. 14. Colies (fig. 24) have the same parts, but still wider and shallower. At first sight the gut of the Coly seems very different from that of the Hornbill. But the vestige of the yolk-duct orients the apex of the middle subsidiary loop of the mid-gut: the anterior and posterior loops of the mid-gut may then be seen as simple shallow curves on the gut. The wide duodenum and the straight rectum, and the veins, are as in the Hornbill and Woodpecker. PASSERIFORMES. I have proceeded only a short way in the examination of the members of this vast group, but those that I have examined show a simple and identical modification of the common type. Parus major (fig. 25) may serve as a fairly generalized example of the Passerine type. The duodenum is a simple loop. The circular coil of the mid-gut shows a tendency to be spirally twisted, the Fig. 25. Parus major ; intestinal tract, x, short-circuiting vessel divided. vestige of the yolk-duct forming the apex of the spiral, and the median mesenteric vein forming the axis of the spiral. The spiral is hardly visible in Parus; it forms less than half a turn. In the Crows and Nutcrackers, and in a very large number of other Passeres, the spiral is long and forms several turns. Between the spiral and the rectum there is a subsidiary loop on the mid-gut where in the primitive type the caeca ran forwards. This in Parus and in all other Passeres I have examined is closely connected with the duodenum, which is folded under it. Frequently a lobe of the pancreas passes across and lies in this subsidiary loop. The loop has a recurrent vein from the middle mesenteric vein, and a short-circuiting vein or veins opening into the duodenal vein. The rectum is short and straight, and where these are present, as in Parus, bears the caeca. The veins are normal. Some Passeres, as, for instance, the Nutcracker, show signs of a subsidiary loop of the mid-gut between the spiral and the duodenum. In others, as, for instance, the Poe Honey-eater (Prosthe-madera), the anterior part of the mid-gut and the spiral are reduced to practically a simple fold, while the last loop of the mid-gut is considerably expanded. |