160 ELEMENTS OF ORNITHOLOGY. 
with our middle toe. It has almost always four joints, but may 
have but three *. 
The fourth toe is comparable with the fourth toe of our foot— 
a digit which, as analogous to the fourth digit of the hand, may, 
at need, be distinguished as the annulus. It has nearly always 
five joints, but may have four T or only three ¢. 
Our own little toe has no representative in the Class of 
Birds. 
When there are but three digits, it is the hallux which dis- 
appears, and when, asin the Ostrich, another is absent, it is the 
second one. This rule is universal save in the genera Ceyx and 
Alcyone, where the second digit is defective or hidden under the 
skin, and the Babbler (Cholornis), where the fourth is defective. 
Disposition of the Digits—Ordinarily birds have three toes 
turned forwards and one, the halluw, turned backwards. Very 
rarely, as in the Swift, all four are turned forwards, when the 
hallux is the innermost of the four. Very often two toes are 
turned forwards and two backwards, constituting what is termed 
a zygodactyle or yoke-toed foot. In this case it is generally the 
first and fourth digits which are turned backwards. In the 
Trogons, however, the first and second toes are turned back- 
wards:and the third and fourth forwards. 
When there are only three toes they all turn forwards, save 
in the genus Picoides, where the fourth is turned backwards. 
Sometimes a digit is what is called “reversible” or “ versa- 
tile ”—that is, it can be turned either way, as is the case with 
the fourth toe in most Owls. 
The hallu« may vary much in its relation to the other toes. 
Jn the first place, it may or may not be on the same level with 
them—the 2nd, 3rd, and 4th toes always being placed side by 
side at the bottom of the so-called “‘tarsus.” If it is on the 
same level with them, it is said to be cncwmbent., If it is 
attached to the hinder side of the tarsus above the level of the 
attachment of the other digits, it is termed elevated, as in the 
Fowl and the Duck. It is generally longer than one or two of 
the other toes, and may be the longest digit of all. It is never 
so long when elevated as wheu incumbent. It may barely 
reach the ground, or it may, as in the Petrels, exist in a rudi- 
mentary condition. 
* As in the Swift. + As in the Gcatsucker. 
{ As in the Swift. 
