POISONOUS SNAKES OF NOKTH AMERICA. 365 



The external layer of the liuiiig of the i)it Leydig foiiud to be a coii- 

 tinuatiou of the outer skin, Avhich, however, upon entering the cavity 

 becomes thin and considerably modiiied. The granular tubercles grad- 

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

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

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

 ramifications of the thick nerve supplying the pit are lost in a granular 

 substance which under high power 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 spaces. 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. 





v-s 



V, 



'/■/tii 



/;•/ 



■■■f( 



/-,' 



^ 



Fig. lU. 



PIECE OF SURFACE OF EPIDERMIS LIXINCi THE I'lT. 



Greatly enlarged, a Smooth, tliiu portion from the pit pi'oper; h tubercular )iiirti(in at the edge. 



( After Leydig. ) 



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

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

 nature, or to what use the animal puts the organ. Future research 

 may reveal it, th(mgh ])erhaps man will never fully comprehend the 

 nature of a sense which he himself does not possess. 



The "loreaF' pit, so called because of its location in that portiou of 

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

 being a character exclusively ])ertaiuing to the Crotalid snakes, its pres- 

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

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

 "death vipers," Mith the exception of the Ehq)s, which I have already 

 characterized. 



Another unfailing character is, of course, the j)reseuce of long curved 

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

 poisonous snakes would manifestly be incomplete were I to omit a 

 description of the i^oison apparatus, a brief outline of its structure is 

 here presented. 



I stated above that Elaps has two permanently erect and perfo- 

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



