1^6 ANIMAL LIFE OF THE BRITISH ISLES. 



Grass Snake (Tropidonotus natrix^ Linn.). 



Before entering upon a description of the greatly feared 

 though harmless Grass, Ringed, or Common Snake, it would be 

 well to say a few words on the structure of Snakes in general, 

 and so avoid some amount of repetition, for in a general way 

 our three species are alike. 



The Slow- worm, our legless Lizard, affords a convenient 

 transition to the Snakes ; but the bony skeletons of Snake 

 and Slow-worm exhibit considerable differences. No Snake 

 possesses a breast-bone, blade-bone, or collar-bone, so that 

 all the ribs are free at their ends, and they are strongly curved 

 to produce the cylindrical form of body. When bulky food is 

 taken the ribs can be flattened out to allow of the necessary 

 distension of the body until digestion and muscular pressure 

 have reduced the bulk. The bones of the skull are connected 

 so loosely that the head can be flattened and widened, so that 

 the mouth can admit prey equal to three times the size of the 

 Snake's head under normal conditions. To assist in the 

 swallowing of such large bodies, the two halves of the lower jaw 

 have no bony connection but are united instead by elastic 

 ligaments, so that each half can be moved independently of the 

 other, and by the alternate movement of the two sides with the 

 teeth all pointing backwards the food is worked back to 

 the throat. There are other teeth on the roof of the mouth 

 which make it difficult for living prey to struggle forward and 

 escape when once it has been seized. The teeth are all thinly 

 coated with enamel, and are not planted in sockets. If they 

 should get broken by the severe work imposed upon them, they 

 are soon replaced by others which lie in reserve. Poison fangs 

 are much larger than ordinary teeth, and the enamel is folded 

 so as to produce a groove down which poison is pressed from a 

 gland into the wound made by the point of the fang. The fang 

 is hinged at its base and ordinarily lies pressed back upon the 



