SOME SUGGESTIONS FOR BIRD STUDY. 107 



different habit. Usually the first toe is turned backward, 



Fig. 31. Diagram of externals of a Falcon, 

 urn, mandible ; c, cere ; N, nosti'il ; -ff.C^ear covert ; 

 th.w. t thumb wing; d, back coverts; <?, wing upper 

 coverts ; <S, secondaries ; P, primaries ; R, rectrices (tail 

 quills) ; A, ankle ; Alt, tarso-metatarsus ; /, first toe. 



Fig. 32. Eye of a 

 Bird, showing the 

 Third Eyelid. 



but sometimes also the fourth, e.g. Owls, Woodpeckers, 

 Cuckoo. In the swifts, whose feet are very short, all four 



