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Show 156 MR. P. CHALMERS MITCHELL ON THE [Jan. 14, to that of the Accipitres ; but this, I think, is superficial, and due to the relation to the common type. The marked features of the divergence from type in the Psittaci consist in the elongation of a definite number of loops and in the matting of these loops together, the loops being folded over each other backward and forward. There is no trace of the formation of a loop supplied by the posterior mesenteric vessel, which is the most striking Accipitrine character. COR ACII FORMES. Of the birds in this group that I have examined, the Owls (fig. 22) and Caprimulgida? are the most primitive, and indeed differ very little from the primitive type. The duodenal loop, as in other Coraciiform birds, is very wide, especially towards its extremity. The circular loop of the gut remains in nearly the primitive con- Fig. 22. Bubo maximus ; intestinal tract. dition, being thrown into a series of short convoluted lobes, supplied by radiating branches from the middle mesenteric vein. In Bubo maximus, where the gut is relatively short, the only subsidiary loop of the mid-gut series that is prominent is the distal loop, along which, as in the common type, the large caeca run forward. In other Owls there is frequently another well-developed subsidiary loop on the part of the mid-gut between the duodenum and the vestige of the yolk-duct. The rectum is straight. The three branches of the portal vein, the duodenal, median, and posterior mesenteric veins, all are in the typical condition. I have not been able to see many of the other birds in this group which possess long caeca. Those without functional caeca display very simple divergences from the common |
