hinder parts of the body and the tail greatly compressed, so as to form a vertical oar. Many, if not all, of the terrestrial species, however, are capable of swimming, and will take to the water of their own accord.
The geographical distribution of the Ophidia is very extensive: they are spread over the whole torrid and temperate regions of the globe. With the exception of the Samoa group, the islands of Polynesia are, however, destitute of them. The Order is divided into five Families, Amphisbænadæ, Boadæ, Colubridæ, Viperadæ, and Hydrophidæ.
Family I. Amphisbænadæ.
(Double-walkers.)
There are found in this Family of Serpents several traces of structure which belong rather to the preceding Order than to the present. Their food consists for the most part of ants and other small insects, the nature of which does not require that these Serpents should possess the power of dilating the mouth and throat, which we have described as common to the Order; hence the upper jaw is fixed to the skull and the inter-maxillary bones, as in the preceding Orders of reptiles, and in the higher animals; while the lower jaw is jointed directly with the skull, and its two branches are soldered together in front. The bony frame of the orbit of the eye is incomplete behind, as we observed it in the Geckotidæ; and the eye is so minute as in most cases to be with difficulty discernible in the adult animal;
