YOUNG BIRDS AND RECORDS OF THE PAST 145 



and Hesperornis, long since extinct, bore teeth along the 

 edges of the beak, which have since been replaced by the 

 horny sheaths with which we are familiar. So far no 

 satisfactory evidence of such structures has been met with, 

 but some years ago I described in the beak of a nestling 

 tinamou (Calodromas), what I believed, and stiU believe, 

 may prove to be vestiges of teeth. These, along the 

 cutting edges of the fore-part of the upper jaw, take the 

 form of a number of tiny, white, closely crowded teeth, 

 and a similar series is met with along the lower jaw. But 

 from that day to this I have never been able to secure 

 the necessary leisure to devote to the work of cutting 

 sections of these jaws for microscopic examination. 



Yet another structure peculiar to the early post-embryonic 

 period must be mentioned. This is the curious roughened 

 " heel-pad " which is found at the base of the shank, or 

 rather the back of the ankle-joint in birds Uke the barbets, 

 the wrynecks, and the woodpeckers. The use of this 

 pad is not quite clear, but it will perhaps be found to be 

 present in the young of all birds which are reared in holes 

 on the bare ground, or in hollow trees, where no real 

 nest is made. They may serve the same purpose as the 

 horny pad which is found on the breast of the ostrich : 

 and as the similar pads on the chest, wrists (" knees "), 

 and true knees of the hind limb in the camels. There is 

 the more reason for this view because the pad in question 

 is so placed that it tends to throw the rest of the foot 

 upwards. But while in the nestling birds the surface of 

 the pad is covered with Httle pointed cones, in the ostrich 

 and camels this surface is smooth. 



The sheath of the beak in nestlings shows two other 

 features which cannot be omitted here. The first of 

 these concerns the compound character of the sheath. 

 10 



