DEVELOPMENT OF ANI 319 



Tx\KS()-METATARSUS 



The mature tarso-inetatarsiis is curiously ridged and 

 grooved, the fourth metatarsal being flattened so as to form 

 a ridge above the other bones. The second metatarsal is 

 much flattened and seems almost to be separated from the 

 others, being connected, particularly on the proximal half, 

 only by a thin, transparent sheet of bone. In the embryo, 

 however, this is not true. As late as the period when the 

 bird leaves the nest all the metatarsals, though totally fused, 

 are still rounded. There is just a slight broadening of the 

 bones and a commencement of the grooves, with no flattening 

 of the fourth metatarsal. 



BILL 



The exaggerated development of the culmen takes 

 place only after the fledgling has left the nest. In the newly 

 hatched chick, the bill is short and swollen, but in all respects 

 typically cuckoo-like. The cuhnen is angled instead of 

 curved, but as the bird grows older the angles decrease and 

 curves take their place. The commissure is greatly curved 

 until the culmen begins to ridge up and then straightens as 

 the ridge forms. The lower mandible is much shorter than 

 the upper and the gonys is narrow and very angular. The 

 projecting hook of the upper mandible gives the young bird 

 a rather hawk-like appearance. The gonys lengthens very 

 slowly, so that at least three months pass after flying before 

 the bird attains its full culmen ridge and its wide flat gonys, 

 which pushes forward so as almost to fill the notch caused 

 by the curved tip of the upper mandible. 



