BATRACHIANS AND REPTILES OF OHIO. 135 



Family : CROTALIDAE. 



This family embraces all of our poisonous snakes. One 

 character is present in them which is found in none of the non- 

 poisonous snakes and hence is an excellent criterion by which one 

 may tell poisonous from non-poisonous forms. Between the eye 

 and the nostril (Fig. i) on either side is a deep pit that is simply 

 an infolded part of the skin in that region. The function of the 

 pit is not known. It has, however, embedded in its walls, termini 

 of nerves which would suggest that it was a sense-organ, of the 

 same category, perhaps, as L,eydig's corpuscles. 



The fangs (Figs. 2 and 3) of the poisonous snakes are simply 

 long, sharp teeth in the upper jaw, perforated with a tube (#') 

 that connects with the duct of the poison gland (#), the whole 

 forming a hypodermic injection apparatus. The poison gland 

 (a} lies above and posterior to the base of the fangs. Above and 

 below it run two large muscles (b and /') which serve to compress 

 the gland and force out the venom. Should a fang be broken off 

 another stands ready to replace it, (Fig. 3.) In our poisonous 

 snakes the fangs are borne on the maxillary bone, which is hinged 

 so that the teeth may be folded back and drawn into a sheath. 

 (Fig. 2,/.) 



When disturbed these snakes throw themselves into a coil 

 from which they strike at the intruder by suddenly straighten- 

 ing the body. They are not able, however, to strike more than 

 half their length, so that a four-foot snake could strike but two 

 feet from coil. 



All our venomous reptiles are sluggish and will strike only 

 when annoyed. The Rattle-snakes are provided with a series of 

 chitinous "rattles," which are simply modified scales. These 

 grow on the end of the tail, being formed continuously. The 

 first one formed in the young snake is known as the " button," 

 it being smaller than the subsequent ones. The rattles are fre- 

 quently broken off, as may well be supposed. The age of the 

 animal hence, for this reason alone cannot be told from the num- 

 ber of rattles even if one rattle were formed a year, which is by 

 no means the case since they vary in their periods of growth. 

 Thus, at times, two or more rattles may be formed within a 

 twelve-month or but one. It may be said that a rattle is formed 

 at each hedding of the skin. 



