ON THE STRUCTURE OF THE FOOT IN BIRDS. 



441 



members of that group. As, however, the account here quoted is, in 

 some points, incorrect, and in others incomplete, and as other errors 

 occur in other authors' works on this subject, I have thought that it 

 might be useful to draw up as complete a list as possible of the differences 

 in these two points of structure now known to exist amongst birds. 



I. The Number of Digits. 



The ordinary number of toes in birds is four, representing the first, 

 second, third, and fourth digits of the normal pentadactyle foot (fig. 1, i). 



W 1 



fldfl 



V 



<7 nt 

 w 



VI 



on 



o 



O V 



A number of birds, however, are three-toed, the reduction in nearly all 

 cases being effected by the suppression of the hallux (fig. 1, n). This 

 may be the case even in birds belonging to zygodactyle groups (fig. 1, in) ; 

 so that we have three-toed "Woodpeckers (e. g. Picoides *) and Jacamars Ib ^ s > 

 (Jacamaralcyon) f. It is not always, however, the hallux that is thus 

 absent in tridactyle birds. In the Kingfishers of the genera Ceyx and 

 Alcyone the foot is three-toed, but the hallux is well developed ; the 



p. 388. 



* By some error Nitzsch (Osteograph. Beitr. p. 102) describes Picoides as lacking 

 the fourth ("letzte") toe. As I have lately shown, however (P.Z. S, June 1882), 

 there is a rudimentary hallux, with its metatarsal, in these birds, though it is quite 

 concealed under the skin, and has, in consequence, been overlooked by previous 

 observers. The existence of a similarly concealed rudimentry hallux in many other 

 birds apparently tridactyle is therefore rendered highly probable. 



t The specific name of Loxia tridactyla (Gmel. Syst. Nat. i. p. 866; Phytotoma 

 tridadyla. Daud. Tr. Orn. ii. p. 366) seems to be a mistake, founded on Bruce's 

 drawing of a bird met with by him in Abyssinia, and mentioned by Buffon (Hist. Nat. 

 Ois. iii. p. 471) under the name of " Le Guifso Balito." This is usually identified as 

 a well-known Abyssinian Barbet (Pogonorhynchus abyssinicus, Marshall, Mon. Capit. 

 pi. 9), with feet of the normal structure. 



