252 



VENOMOUS ANIMALS 



The poison-fang projects downwards and backwards in the closed 

 mouth, being firmly attached to the alveolar process, and it is en- 

 tirely due to the free mobility of the cranial bones one on the other 

 that the fang can be placed in such a position as to be able to enter 

 the skin of the victim. 



The act of striking, as described by Weir Mitchell in Crotalus, 

 is as follows :^ — In preparing to strike, the snake first of all throws 

 itself into its v/ell-known characteristic attitude, with the lower 

 part of the body coiled, the tail slightly projecting, and the head 

 raised a few inches. 



The tongue now darts backwards and forwards, and the air of 

 expiration, in passing through the narrow glottis, produces the 

 characteristic hissing. The muscles on the convexity of the coils 

 now contract and straighten the snake, so that the head is thrust 

 suddenly upwards, forwards, or downwards, as required. The 

 maximum thrust is half of the body-length, the usual one-third; 

 but the reptile judges this for itself, and sometimes makes mistakes. 

 The jaws are widely separated, and the head is bent back on the 

 cervical vertebrae, and a muscle called the spheno-pterygoid, which, 

 passing from the basal orbito-sphenoid region backwards, to be 

 inserted into the inner dorsal surface of the pterygoid, contracts, 

 and draws forward the pterygoid, thus pushing upwards the ecto- 

 pterygoid (transversum), and causing the superior maxillary bone 

 to rotate forward on its lachrymal articulation, and thus to erect 

 the fang. This motion, when it reaches its limit, is checked by 

 ligaments, and now the lachrymal yields a little to the force applied 

 to the maxilla, with the result that the whole muzzle of the snake 

 is elevated, and produces the curious appearance which it has 

 when preparing to strike. The fang now enters the flesh of the 

 victim, and the head of the snake is drawn violently backwards, 

 too much action being prevented by the muscles of the spine. In 

 the meanwhile the spheno-pterygoid, acting from the pterygoid, 

 and together with the external pterygoid, rotates the maxilla and 

 pulls the fang backwards, and so drives it deeply into the flesh. 



The lower jaw now closes on the bitten part, and this act squeezes 

 the fluids from all parts of the glands forward into the duct, and 

 not merely deepens the v/ound, but injects the venom forcibly 

 into it. 



The snake then has to disentangle itself, and in so doing may 

 lose its fang. But this is of no moment, for fangs are shed naturally, 

 and there are a number of tooth-germs in different stages of develop- 

 ment ready to take the place of the lost tooth. 



Sometimes the fangs have not been properly erected, and there- 

 fore only their convex borders touch the skin of the victim, in 

 which case the venom will flow on to the skin, but the fangs will 

 not penetrate. 



The Venom. 



Collection. — ^The venom can be collected by making the snake 

 strike a watchglass covered with a thin, tightly stretched piece of 



