i8o GENERAL ORNITHOLOGY part n 



"the shank." These points must be ingrained in the student's 

 mind to prevent confusion (Fig. 34 his). 



The digits of the foot, or toes, upon which alone most birds walk 

 or perch, consist of certain numbers of small bones placed end to 

 end, all jointed upon one another, and the basal or proximal ones 

 of each toe separately jointed either with the principal or the acces- 

 sory metatarsal bone. Like those of the fingers, these bones are 

 called plialanges (Lat. phalanx, a rank or series) or internodes (because 

 coming between any two joints or nodes of the toes). The further- 

 most one of each almost invariably bears a nail or claw (unguis). 

 The phalanges are of various relative lengths, and of a variable 

 number in the same or different toes. But all these points, being 

 matters of descriptive ornithology rather than of anatomy proper, 

 are fully treated beyond, as is also the special horny or leathery 

 covering of the feet usually existing from the point outward. We 

 may here glance at the 



Mechanism of these Bones. — The hip is a ball-and-socket joint, 

 permitting roundabout as well as fore-and-aft movements of the 

 whole limb, though more restricted than the shoulder- joint. The 

 knee is usually a strict ginglymus (Gr. yty-yXv/io's, gigglumos, hinge) 

 or hinge-joint, allowing only backward and forward motion ; and so 

 constructed that the forward movement of the leg is never carried 

 beyond a right line with the femur, while the backward is so exten- 

 sive that the leg may be quite doubled under the thigh. In some 

 birds there is a slight rotatory motion at the knee, very evident in 

 certain swimmers, by which the foot is thrown outward, so that the 

 broad webbed toes may not " interfere." The heel or ankle-joint is 

 a strict hinge ; its bendings are just the reverse of those of the knee ; 

 for the foot cannot pass back of a right line with the leg, but can 

 come forward till the toes nearly touch the front of the knee. In 

 some birds the details of structure are such that, with the assistance 

 of certain muscles, the foot is locked upon the leg when completely 

 straightened out, so firmly that some little muscular effort is required 

 to overcome the obstacle ; birds with this arrangement sleep securely 

 standing on one leg, which is the design of the mechanism. The 

 jointing of the toes with the prongs of the metatarsus is pecuhar; 

 for the articular surfaces are so disposed in a certain obliquity, that 

 when the toes are brought forwards, at right angles or thereabouts 

 with the foot, they spread apart from each other automatically in 

 the action, and the diverging toes of the foot thus opened are 

 pressed upon the ground or against the water. When the toes aie 

 bent around in the opposite direction, they automatically come to- 

 gether and lie in a bundle more or less parallel with one another, 

 besides being each bent or flexed at their several nodes. This 

 mechanism is best marked in the swimmers, which, for advantageous 



