HIGH SCHOOL ZOOLOGY. 113 



from which it projects backwards. Tlius the articulation of 

 the lower jaw, which is composed of two movable halves, i.s 

 situated behiml the head, and the gape is consequenlly ex- 

 tremely wide. 



20. The Ophidia are destitute of the Eustachian tubes and 

 tympanic cavities, the outer ends of the columellse merely 

 'ibutting against the quadrates. 



Most of the snakes lay eggs, which are batched without the 

 aid of the mother, but some of the venomous snakes, as well as 

 fresh-water forms, bring forth their young alive, and these are 

 in certain instances taken care of by the mother. 



21. Apart from the naiTOW-mouthed Typhlops and its allies, 

 and the Pythons, Boas, etc., with rudimentary hind-limbs, the 

 Ophidia fall into three groups, the extremes of which are 

 formed by the poisonous rattle-snakes on the one hand with 

 few canaliculate poison-fangs, and the harmless Colubridse with 

 numerous non-perforated teeth, on the other, while the various 

 poisonous snakes with grooved teeth, like the brilliantly-coloured 

 Bead-snake of the Southern States (Maps), the spectacled snake 

 of India (Naja), and the flat-tailed sea-snakes of tropical seas 

 (IIi/droj)his), occupy an intermediate position. In this region 

 only the. extreme forms are represented, the Crotalidse and 

 the Colubridje — the former embracing the rattlesnakes and 

 copperheads, the latter all our numerous hannless snakes. 



22. Crotalus horrklus, the banded rattlesnake, is marked by the head 

 being covered with scales instead of regular shields, and by its alternate 

 bands of two shades of brown. As in all the more venomous snakes the 

 head is sharply marked off from the body by a neck. The movements 

 are much more sluggish than in the Colubrid;v, the greater agility of 

 which compensates them for the absence of the peculiar weapons of 

 the rattlesnake. One of the most characteristic features of the genus is 

 the rattle formed of singular epidermal scales, the function of which has 

 been much discussed. Observers are not agreed whether it is used to 

 attract prey or to frighten away enemies. It is possibly useful for both 



