THE SNAKES 197 



is the only large country in warm or temperate latitudes 

 entirely free of dangerous snakes ; it is, however, inliab- 

 ited by a number of harmless kinds. 



After the student has been referred to the great vari- 

 ety of limbless lizards that crawl in what appears to 

 be typical serpentine fashion, a very natural question 

 may arise — What are the points of differentiation dis- 

 tinguishing the true snakes from the legless lacertilians ? 

 The differences are not elaborate. The chief characters 

 involve the bones of the head — particularly those of the 

 lower jaw. Among snakes the lower jaw is not single, 

 as with the lizards; it is composed of two elongated, 

 nearly straight bones that are connected in the front 

 merely by an elastic ligament. Besides this arrange- 

 ment, the suspension of the lower jaw bones and the 

 attachment of the upper ones, too, provide for great 

 elasticity and enable a serpent to engulf its prey entire — 

 often an animal four or five times the diameter of its 

 neck. This swallowing apparatus of the serpent shows 

 marked speciahzation among reptiles. The process of 

 engulfing the prey is extremely simple and ingenuous, 

 though little understood. About this characteristic has 

 originated a string of ridiculous stories. Let us sup- 

 pose a snake with a neck about as thick as a man's fore- 

 finger were about to swallow a large rat. This would 

 be an easy task. Usually, the prey is grasped by the 

 snout when the performance conunences. One of the 

 upper jaw bones and the corresponding lower jaw bone 

 reach forward, the bones close upon the prey inserting 

 the recurved teeth, when this side of head is pulled 

 back drawing the animal a short distance into the mouth ; 

 the process is repeated with the other side of the head, 

 each side working in alternation while the quarry is 

 pulled into the mouth and forced into the throat, which, 



