SCALED REPTILES SNAKES. 417 



pythons. In temperate regions snakes become gradually less common as we 

 proceed north in the one hemisphere and south in the other ; but, with the ex- 

 ception of New Zealand and the polar regions, the group may be considered 

 to enjoy practically a world-wide range. Nine families of snakes are recognised 

 by zoologists ; and these include a very large number of genera, and probably 

 more than fifteen hundred distinct species. With such a vast assemblage, it is 

 of course impracticable in our limited space to do more than notice the leading 

 and most important types. And even treating the group in this manner, 

 there is considerable difficulty in giving the student a proper idea of the 

 subject, on account of the close structural similarity between many of the 

 families. To understand snakes thoroughly requires an intimate acquaintance 

 with a mass of structural details, and the acquisition of a host of technical 

 terms ; and these can only be acquired by a patient practical study of the 

 group. 



At the head of the sub-order are now placed the two comparatively unim- 

 portant families of blind-snakes, which differ from all the rest in lacking 

 teeth in either the upper or the lower jaw. In form, these 

 snakes are cylindrical and worm-like, with relatively short Blind-Snakes. 

 heads and tails ; while in habits they likewise resemble Families 

 worms, passing most of their lives in tunnels driven by Typhlopidce and 

 themselves beneath the surface of the ground. Here they Glanconiidce. 

 subsist by feeding upon such insects or their larvse as they 

 happen to encounter, ants being apparently a very favourite dish. Dull, 

 rainy weather will occasionally tempt them above ground. Living in such 

 subterranean haunts, the large inferior transverse shields of ordinary serpents 

 would be useless, and we accordingly find the bodies of the blind-snakes 

 covered all round with scales of equal size, although there are some large 

 shields on the fore part of the head, beneath a pair of which are buried the 

 rudimental and useless eyes. Unlike most of their kindred, these snakes 

 cannot expand their jaws ; and the small aperture of the mouth is placed on 

 the under side of the head. That these snakes are nearly related to limbed 

 reptiles is proved by the retention in the skeleton of more or less distinct 

 vestiges of the pelvis. An important feature in the structure of the bony 

 palate, which need not be considered in detail here, suffices to distinguish 

 them from all the other members of the sub-order, to which it seems likely 

 that they have no close relationship. Indeed it is quite probable that whereas 

 the blind-snakes are descended from one group of lizard-like reptiles, all 

 other ophidians may trace their origin to a second. In the first of the two 

 families into which the blind-snakes are divided, it is the lower jaw which has 

 lost its teeth, and the pelvis is represented by a single pair of bones. The 

 family, which includes three distinct genera, with about a hundred species, 

 ranges over all the warmer countries ; one species of the large typical genus 

 Typhlops occurring in Southern and Eastern Europe. On the other hand, 

 in the Glauconiidce it is the upper jaw that has no teeth, while two pairs of 

 bones remain to represent the pelvis. The family includes only the genus 

 Glaucouia, of which there are nearly thirty species ranging over Africa, the 

 south-west of Asia, and America. 



Of far more importance than the last is the great family of boas and 

 pythons, which include the largest of all living snakes, and are characterised 

 by their habit of killing their prey by crushing it in the folds of their bodies. 

 Like the blind-snakes, these huge serpents retain external vestiges of the 

 hind-limbs, and likewise internal traces of the pelvis ; but as they differ con- 

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