232 CHARACTERS OF VERTEBRATE ANIMALS 



has already been dealt with, i.e. the tear-chamber of the eye. 

 The organs of hearing consist solely of the membranous laby- 

 rinth, the sound-conducting middle ear being entirely absent. 

 The tongue appears to be used as an organ of touch. 



As at least a thousand species of snakes are known, it will 

 only be possible here to mention a few of the more important 

 forms. The following groups can be recognized: — i. Simple- 

 toothed Snakes; 2. Whip-Snakes; 3. Cobras and Coral Snakes; 

 4. Sea-Snakes; 5. Vipers; and 6. Blind-Snakes. 



I. Simple-toothed Snakes are non-poisonous forms, in which 

 both upper and lower jaws are provided with rows of solid, hook- 

 like teeth. Here are included the giant snakes known as Pythons 

 and Boas (fig. 145), which are found in the tropical regions all 

 round the world, but are especially abundant in South America. 

 Among the species may be mentioned the Indian Python 

 {Python molurus), which may attain a length of 30 feet, the 

 somewhat longer West African Python [P. sebce), the Anaconda 

 {Euneees murinus) of tropical South America, which is credited 

 with being the largest of living snakes, and the much smaller 

 Boa Constrictor {Boa constrictor) from the same region. All 

 these forms kill their prey by crushing, and it may also be 

 noted that their skins are very beautifully marked with elaborate 

 patterns. TJiey are the only snakes which possess externally 

 visible remains of the hind-limbs. 



Not very distantly related to the giant snakes are the two 

 harmless forms (fig. 146) which are found in Britain, i.e. the 

 Grass Snake {Tropidonotus natrix) and the Smooth Snake 

 {Coronella Icsvis). The former is commonly met with in the 

 neighbourhood of fresh water, and it is a good swimmer. The 

 frog is the favourite article of diet, but small mammals, birds, 

 and fish are also eaten. This snake can readily be distin- 

 guished from the poisonous Adder by its colour and markings. 

 The darker upper surface is usually brownish or greenish, marked 

 by darker spots or narrow transverse bands, while at the back 

 of the head is a good-sized yellow or orange patch on each side, 

 behind these again being a broad dark " collar ". The under- 

 side of the body is mottled, and of much lighter hue. 



The Smooth Snake is not common in Britain, but is some- 

 times found in dry places in the southern English counties. It 

 is smaller than the Grass Snake, and may readily be distinguished 



