STRUCTURE AND POSITION OF THE TOES. 49 



terior toe (3t) = third toe ; outer anterior toe (4t) = fourth toe. In birds 

 with the hind toe reversed, the same order is obvious : only, inner anterior 

 toe = It, etc. In zijgodactyli (except Trogonklce), inner hind toe=lt; 

 inner front toe = 2t ; outer front toe = 3t ; outer hind too = 4t. Now 

 when the number of toes decreases, tbe toes are always reduced in the 

 same order: thus, in all three-toed birds. It is wanting: in the two-toed 

 birds It and 2t are wanting. This is proven by the 



§ 86. Number of Joints, or number oi plicdanges (§ 72, /) of the toes. 

 The constancy of the joints in birds' toes is remarkable, one of the strong- 

 est expressions we have of the highly monomorphic character of the class 

 Aves. In all birds. It has two joints (not counting the accessory metatar- 

 sal) . In all birds, 2t has tJiree joints. In nearly all birds, 3t has /ortr joints. 

 In nearly all birds, 4t has five joints. The only exceptions to this, consist 

 in the lessening of the joints of 3t by one, and the lessening of the joints 

 of 4t by one or two. So in all cases, where the joints do not ran 2, 3, 4, 5, 

 for the toes from 1st to 4th, they run either 2, 3, 4, 4, or 2, 3, 3, 4, or 2, 

 3, 3, 3. This variability in number of the internodes is confined (wholl}'?) 

 to the order Strisores. Our examples are in the sub-families Cupselinoi and 

 Cajyrimidgince (which see; see also figs. 119 and 122). This admiralde 

 conservatism enables us to always determine what toes are missing, in birds 

 with less than four; thus, in Picoides, the hind toe, though seemingly It, 

 is evidently 4t, because 5-jointed ; in the ostrich, with only two toes, 3t 

 and 4t are seen to be preserved, because they are respectively 4- and 5- 

 jointed. (In fig. 8, the dotted line 1 indicates the first series of phalanges 

 of all the toes ; dot-line 2, the second ; the correspondence of the remaining 

 phalanges is seen at a glance.) 



§ 87. The position of the toes, other than in respect of their direction, 

 is important. In all birds the front toes are on the same level, or so 

 nearly so, that the difference is not notable. And the same may be said of 

 the hind toes, when there are tivo, as in Scansores. But the hind toe, when 

 present and single, varies remarkably in position, and must have sjoecial 

 notice, as this character is important in taxonomy. The insertion of this 

 toe varies, from the very bottom of the tarsus, where it is on a level with 

 the front toes, to some distance up the tarsus. When flush with the bases 

 of the other toes, so that its whole under surface touches the ground, it is 

 said to be incumbent. When just so much raised that its tip only touches 

 the ground, it is called insistent. When so high up that it does not reach 

 the ground at all, it is termed remote (amotus). But as the precise position 

 varies insensibly, so that the foregoing distinctions are not readily per- 

 ceived, it is practically best to recognize only two of these three conditions, 

 and say simply, "hind toe elevated," when it is inserted appreciably above 

 the rest, or "hind toe not elevated," when its insertion is flush with that of 

 the other toes. In round terms : it is characteristic of all Insessores to have 

 the hind toe down ; it is characteristic of all other birds to have the hind toe 

 UP (when present). The exceptions to the first statement are extremely 



KF,Y TO N. A. BIRDS. 7 



