of the Foot in Birds. 



387 



third and fourth toes have only three phalanges each 

 (2, 3, 3, 3), and the Goatsuckers and the Sand-Grouse^ in 

 which the fourth toe only has the number thus reduced 

 (3,3,4,3)- 



Prof. Huxley has described in these words ^ the nature of 

 the variations from the normal structure of the Avian pes, as 

 regards the number of digits and phalanges composing it, 

 exhibited by various members of that group. As, however, 

 the account here quoted is, in some points, incorrect, and in 

 others incomplete, and as otlier 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. Tlie Number of Digits. 

 The ordinary number of toes in birds is four, representing 

 the first, second, third, and fourth digits of the normal pen- 



Fisr. 1. 



m 



CD I 



m 



IV in: 



IV 



D 



(7 



IV 



,^0^ 



Iff 



tadactyle foot (fig, 1, i). A number of birds, however, are 

 three-toed, the reduction in nearly all cases being effected by 

 the suppression of the hallux (fig. 1, ii). This may be 

 the case even in birds belonging to zygodactyle groups 

 (fig. 1, in) ; so that we have three-toed Woodpeckers (e. g. 



* ' A Manual of the Anatomy of Vertebrated Animals,' pp. 29G, 297. 

 London, 1871. 



