OX THE STRUCTURE OF THE FOOT IN BIRDS. 443 



Fig. 2. 

 i i iff iv 



Ibis, 1882, 

 p. 389. 



/7DQ 



a w 









D 



\ 



n 



(7 V ^ 



I- PJ 



In the true Swifts (i. e. the genera Cypselus and Panyptila)*, though 

 not in the rest of the Cypselidae, the number of phalanges in each digit 

 external to the hallux is three, the formula thus becoming 2, 3, 3, 3 

 (fig. 2, in). In the other genera of Swifts the normal number of 

 phalanges obtains, as already correctly stated by Mr. Sclater f. 



In the Pteroclidse and true Caprimulgidse, finally, the formula is 2, 3, 

 4, 4 (not 2, 3, 4, 3, as stated by Prof. HuxleyJ), the fourth digit being 

 one short of the normal number of phalanges (fig. 2, iv). The anomalous 

 genera Steatornis, ^Egoiheles^ Nyctibius, &c. are normal as regards the 

 structure of their feet , as also are Thinocorus and Attagis. 



Nitzsch, who must have been misled by a badly articulated skeleton, 

 ascribes four joints each to all the toes, both of Struihio and Casuarius ||. 

 He was in doubt therefore as to which digits were represented in these 

 forms. As a fact, I need scarcely remark, the normal number of 

 phalanges (4, 5 and 3, 4, 5 respectively) is present in both these birds, 

 though in museum specimens a joint or two is often missing. In many 

 Ostriches, however, the nail of the outer toe is quite absent, and in 

 others very small ; so that their foot is evidently tending to become, like 

 that of the Solipeds, reduced to a single toe, in this as in other cases 

 the third. 



Ibis, 1882, 

 p. 390. 



* Nitzsch, so long ago as 1811, pointed out this fact, as well as the reduction in 

 Caprimulgus (" Ueber die Gliederung der Fusszehen, besonders im Ziegenmelker und 

 in der Mauerschwalbe," Osteogr. Beitr. pp. 101-105). 



t P.Z. S. 1865, p. 596. 



\ Possibly misled by an error in the figure of the skeleton of Syrrhaptes in Prof. 

 Parker's memoir " On the Osteology of the Gallinaceous Birds and Tinamous " (Tr. 

 Z. S. v. pi. 38), where the outer toe is represented as consisting of three joints only, 

 though in the text (p. 203) the correct number is accurately stated. 



Cf. Sclater, P. Z. S. 1866, p. 124. 



|i Op. cit, p. 102. 



