Page:Popular Science Monthly Volume 13.djvu/740

720 known as the "ploughshare" bone formed by the union of several of its segments into a terminal mass for the support of the rudder-quills and of the oil-gland. Several very marked characteristics are to be seen in the hind-limb, to which, without entering deeply into osteological details, we may draw attention. Opening into the hollow shafts of the stronger bones—a character common to those of the wing and parts of the spine—there are to be found small pores, the air-passages by which the air-sacs, themselves extensions of the air-tubes of the lungs, are prolonged into the bones. In the skull also we find numerous air-cavities; these, however, are filled, not from the lung air-system, but from the nasal and ear chambers. No one who has examined the leg-bone, often called the "drumstick" (technically known as the tibia), of a common fowl, can have failed to observe the great ridge, or prominent crest, on the front of its upper extremity, or how easily the pulley-shaped articular surface of its lower end separates off from the shaft in the young bird, especially if the bone has been boiled or macerated for some time in water. This peculiarity vanishes when the fowl attains to its full growth; but till then the separation remains, as if to assert the right of the extremity to be considered, what in reality it is, a separate and distinct bone, the sole representative of a colony of ossicles (corresponding to the bones of the heel in the human foot) once existing in its grandsires at this spot, which for reasons of expediency has here coalesced with its long neighbor. On its outer side the leg-bone is always accompanied by a very slender bone, known as the fibula, attached only at its upper end, tapering gradually to a point about the middle of its fellow. Lastly, to the leg-bone immediately succeeds the hock-bone, the beautiful conformation of whose lower end into the resemblance of a triple pulley, for the articulation of the toes, is a mark by which we can unhesitatingly say that it belonged to a bird.

Bearing in mind these peculiarities, for whose detection no very deep scrutiny is required, which are but a few, yet sufficient for our present purpose, of the more striking characteristics to which the members of the Avian family more or less closely conform, we shall now for a little turn our attention to that other division of the animal kingdom with which we have in the title of this article contrasted the bird.

The reptiles are a wonderfully interesting group on account not only of the marvelous variety of their habits and modes of life, but also of their manifold diversity of form. Our country, in common with the rest of Northern Europe, can claim to be the habitat of but few examples of this tribe, whose home is under warmer latitudes; and consequently only limited opportunities present themselves to the European student for becoming acquainted with their habits and animated forms, unless he happens to live within reach of the menageries of the Zoölogical Societies of London, Berlin, Paris, or Amsterdam; those who are unfortunately distant from such interesting educational centres must