XIII 



PHYLUM CHORDATA 



393 



Toucans. It is most commonly bent downwards at the tip, but 

 may be straight or curved upwards, as in the Avocet, or bent to 

 one side as in the New Zealand Crook-billed Plover. It is some- 

 times, as in the Toucans, brilliantly coloured, and there may also be 

 bright coloration of the cere, as in the Macaws, and of naked spaces 

 on the head, as in the Cassowaries. In the latter the head is produced 

 into a great horny prominence or " casque," supported by an ele- 

 vation of the roof of the skull. The cere is frequently absent. The 

 nostrils are placed at the base of the beak except in Apteryx, in 

 which they are at the tip. 



The essential structure of the wing apart from its feathers is 

 very uniform. As a rule all three digits are devoid of claws, 

 as in the Pigeon, but the Ostrich has claws on all three digits ; 

 Rhea on the first and sometimes on the second and third ; the 

 Cassowary, Emu, and Kiwi (Fig. 999, B) on the second ; the Crested 

 Screamer (Chauna) and two other species, and, as a rare abnorm- 

 ality, the Common Fowl and Goose, on the first. With these 

 exceptions, the hand of the adult bird has lost all the characters 

 of a fore-foot; but in the young of the Hoatzin (Opisthocomus) 

 claws are present on the first two digits (Fig. 999, A), which are 



FIG. 099. A, Wing of nestling of Opisthocomus ; B, Wing of adult Apteryx ; both from 

 the inner (ventral) aspect, cb, 1, first cubital remex ; dg. 1, dg. %, dc/. 3, digits ; pr. ptgm. 

 pre-patagium ; pt. ptgm. post-patagium. (A, after Pycraft ; B, after T. J. Parker.) 



sufficiently mobile to be used in climbing. Besides the true claws 

 horny spurs are sometimes present on the carpus and metacarpus. 



There is almost every gradation in the proportional length of 

 the hind-limb, from Birds in which nothing but the foot pro- 

 jects beyond the contour feathers, and even the toes may be 

 feathered, to the long-legged Storks and Cranes, in which the distal 



