36 THE STORY OF THE BIRDS 



considerably in size in the different groups, in 

 some consisting of a series of fine reticulations, 

 in others of oblong plates, or of both combined, 

 whilst in others yet again the surface of the 

 metatarsal is smooth and " booted." Following 

 the metatarsals come the toes, which form that 

 part of the foot upon which a bird stands or 

 walks. Owing to the transitory character of the 

 fifth metatarsal a bird never shows any trace of 

 a fifth toe. The first toe in not a few cases is 

 aborted, in the Ostrich the second toe is want- 

 ing, whilst in two genera of Kingfishers the second 

 toe is aborted : the only instance known of an 

 aborted fourth toe is presented by the Timeliinae, 

 genus Cholornis. The hind toe (Hallux) has two 

 joints or phalanges only, the second toe or digit 

 possesses three, the third toe four, and the fourth 

 toe five joints. The Swifts, however, are excep- 

 tional, having only three phalanges in each of 

 the anterior toes, whilst in the typical Goatsuckers 

 and the Sand-Grouse the fourth digit possesses 

 only four. The toes of birds are modified in 

 an immense number of ways to bring them into 

 harmony with the conditions of life and the 

 various habits of their possessors. In numbers 

 of birds either the hallux or the fourth digit is 

 reversible at will, as in the Owls and to a lesser 



