SEC. Ill EXTERIOR PARTS OF BIRDS 189 



of it are in certain genera of Cypselince, Fig. 40, where the ratio is 

 2, 3, 3, 3, of Caprinmlr/incc, Fig. 41, where it is 2, 3, 4, 4 ; and the 

 petrel family, with 1, 3, 4, 5. Such admirable conservatism enables 

 us to tell what toes are missing in any case, or what ones are out of 

 the regular position. Thus, in Pko'kles, the hind toe, 

 apparently 1/, is known to be 4^, because it is five- [(7 



jointed ; in a trogon, the inner hind toe is 2t, being | . 



three-jointed ; in the ostrich, with only two toes, J^^ 



Zt and At are seen to be preserved, because they fi-'^^f/^^x 

 are respectively four- and five-jointed. Besides this \\M j) 

 interesting numerical ratio, the phalanges have other \? 

 inter-relations of some consequence in classification, 

 resulting from their comparative lengths. In some lan Jes°' ol'^' cnlse- 

 families of birds, one or more of the basal or proximal ^"« *""*: 2, 3, 3, 3. 

 phalanges (those next to the foot — opposed to distal, 

 or those at the ends of the digits) of the front toes are extremely 

 short, being mere nodules of bone (Fig. 40) ; in other and more 

 frequent cases, they are the longest of all, as in Figs. 34, 41. 

 On the whole, they generally decrease in length from proximal to 

 distal extremity, and the last one of any toe is quite small, serving 

 merely as a core to the claw. The difference in the lengths of the 

 several phalanges, like that of the digits themselves, makes the 

 toes more eiScient in gTasi)ing, since they thereby 

 clasp more perfectly upon an irregular object. The 

 design and the principle are the same as seen in 

 the human hand, in which model instrument the 

 digits and their respective joints are all of difierent 

 lengths. 



The Position of the Digits, other than in re- 

 spect to their dtredion, is important. In all the birds 

 front toes are inserted on the metatarsus on the same 

 ^ level, or so nearly in one horizontal plane that the 



xj>5^ difference is not notable. The same may be said of 



Fig. 41. — Pha- the hind toes when they are a pair, as in zygodactyle 

 gine'^foot, 2^^3" 4'^V birds. But the hind toe, or hallux, as it is called, Avhen 

 After Sciater. present and single, varies remarkably in position 



with reference to the front toes ; and this matter requires special 

 notice, as it is important in classification. The insertion of this 

 digit varies from the very bottom of the tarsus {metatarsus), where it 

 is on a level with the front toes, to some distance up that bone. 

 When the hallux is flush with the bases of the other toes, so that its 

 whole length is on the ground, it is said to be incumhenf. When 

 just so much raised that its tip only touches the ground, it is called 

 insistent. When inserted so high up that it does not reach the 

 ground, it is termed remote (amotus) or elevated. But as the precise 



