POISONOUS SNAKES OF NORTH AMERICA. 365 



The exterual layer of the lining of tiie i)it Leydig found to be a coil-. 

 tinuatiou of the outer skin, which, however, upon entering* the cavity, 

 becomes thin and considerably modified. The gianular tubercles grad- 

 ually disappear toward the bottom, and the surface is found to be com- 

 posed of large angular epidci mis plates containing nuclei (fig. 10). 

 Underneath this he found a. layer of (connective tissue, in which the fine 

 ramifications of the tliick ner\e supplying the pit are lost in a granular 

 substance which under high iiower reveals itself as containing numerous 

 true, rounded, but pale nuclei. The granular substance he found 

 arranged around the nuclei in such a way as to form groups or islands 

 of various forms and sizes separated by light narrow si)aces. These 

 structures can only be regarded as terminal ganglions, and it does not 

 seem doubtful that we have here to do with a true sense organ. 



•'T <■' ■ ■ ■' / ' -jr'-^ I.' x^\ Si y 



..-' y ■ ■'/.r/'l'.i ^--^ . J ^ 



""^. ... L_. ) ■ 



PIECE OF SURFACE OF EI'IUEKMIS LliMNu lUK PIT. 



Greatly t-rlarged. a Smooth, thin portion from the jiit proper; h tubercular i)ortion at ( he edge. 



{ After Leydig. ) 



Wherein this " sixth sense" consists we do not know, nor do we know 

 of finything in the habits of these snakes which would indicate its 

 nature, or to what use the animal i)ats the organ. Future research 

 may reveal it, though ])erhaps man will never fully comprehend the 

 nature of a sense which he himself does not possess. 



The "loreal" pit, so called because of its location in that portion of 

 the snake's face in herpetological terminology known as tlie "lores,'' 

 being a cliaracter exclusively ])ertaining to the Crotalid snakes, its pres- 

 ence in any of our North American snakes at once designates it as a 

 tlangerously poisonous snake. It is an unfailing character of our native 

 "death vipers," with the exception of the IJhq)s, which I have already 

 characterized. 



Another unfailing character is, of course, the presence of long curved 

 fangs in the anterior jwrtion in the upper jaw. Since an account of our 

 poisonous snakes would manifestly be incomj)lete Avere I to omit a 

 description of the poison apparatus, a brief outline of its structure is 

 here presented. 



I stated above that Ehtps has two permanently ei-ect and i)erfo- 

 rated fangs in the anterior portion of tin upper jaw. In the Pit Vipers 



