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The head is covered either with scales like on the rest of 

 the body, or with large plates of regular form, or with various 

 gradations between these two classes of covering. 



In the greater number of vipers, there is no trace of the 

 regular-shielded crown possessed by the majority of snakes, 

 the head being scaly like the rest of the body ; the Erycidce 

 and AcrochordidcB have also scaly , heads ; the burrowing 

 snakes have an incomplete shielded covering. In two snakes 

 of very opposite habits, the head-covering is composed of 

 large scales simulating the arrangement of shields ; Xeno- 

 peltis unicolor, a burrowing snake, and Peltopelor macro- 

 lepis, a tree-viper, both solitary species of their genus, 

 have large triangular scales occupying with considerable 

 regularity the place of the head-shields ; in the latter snake 

 they may indeed be said to be shields simulating scales. 

 The lowest family of snakes, the TyphlopidcB, is distinguished 

 by a type of head-shielding quite different from that found 

 in other families ; these ' blind' snakes have become degraded 

 by an entirely subterranean life. The normal arrangement 

 of head-shields, about to be described, is sketched out in 

 the skinks, a family of lizards of Ophidian appearance, from 

 which the snake-class has evidently developed. 



The head-shields appear to have formed round a central 

 shield, the vertical, which is of a shape departing but little 

 from that of a pentagonal heraldic shield, base in front, 

 apex behind. It sometimes becomes bell-shaped by the 

 rounding of the posterior angles or hexagonal by the 

 addition of a salient angle in the base-line. Behind this 

 are the two occipitals, large, elongated, and either rounded 



proportion are found to be deficient in this member. I have seen 

 several cobras with as little as two inches left of tails which should 

 have been nine inches in length. It is probable that this mutilation 

 is caused by a mungoos biting off the tail of a snake which has fled 

 into a hole not quite large enough to shelter his whole length. 



