304 SNAKES. 



rattle ; and we will again imagine the whole tip of a finger 

 to be covered with a round nail-cap, proceeding from the 

 first joint, and to have grown so from birth. In growing out, 

 this curious, cup-like nail, being never cut, would become 

 hollow like a thimble. Pointed or tapering it would of 

 course be, because, as the baby finger grew, the base or new 

 portion of nail grew larger with it. We will also suppose 

 that the joint whence the nail sprang was in constant 

 activity, and so articulated that it could move with a quick 

 and regular action or vibration ; the hollow nail-cap, having 

 attained a certain size, would become withered, and (as the 

 constant bending of a piece of card or metal in time divides 

 it) would be worn, and at length detached at its base. 

 Meanwhile the growth of nail has not been arrested, but a 

 new cap is forming within. The old, dry, and withered cap 

 has now nothing to retain it, and would drop off, on account 

 of its simple, conical form, like a loose-fitting thimble. But 

 Dumeril explains to us that the terminal bones of the rattle- 

 snake's spine presenta peculiar form, several of them coalescing. 



' Dans les Crotales cette extremite de la queue, au lieu d'etre 

 pointue, se trouve comma tronquee, et, par une bizarrerie que nous 

 n'expliquons pas, il paraitrait que les trois dernieres pieces de la 

 colonne vertebrale se seraient soudees entre elles, et comme aplaties 

 pour composer un seul os triangulaire, avec trois bourrelets lateraux 

 simulant des restes d'apophyses transverses des vertebres, ainsi 

 qu'on les voir souvent dans les trois dernieres pieces du coccyx chez 

 I'homme. Cet os anormale a ete diss^que chez un Crotale, on a 

 reconnu qu'il est recouvert d'une sorte de matiere cartilagineuse 

 dans laquelle aurait ete secretee la substance cornee, comme un 

 epiderme solide, qui conserve en effet exterieurement la forme de 

 la piece osseuse, sur laquelle elle a ete en quelque sorte moulee et 

 qu'elle semble destinee ainsi a proteger centre I'exfoliation, comme 



