29 



tooth of our common Black Snake, ( Coluber constrictor, Linn.,) 

 from an alcoholic specimen, procured for me by my friend, Mr. 

 F. W. Putnam, of Salem. This preparation is drawn in the plate. 



This egg-tooth represents in its structure all the character- 

 istics of the teeth of snakes and lizards generally ; and being at 

 the same time small enough to allow a high power of the 

 microscope, it is the best object I know, for studying that kind 

 of teeth. 



The central cavity is bottle-shaped, and is entirely filled with 

 the yellowish pulp, in which were seen the contours of large 

 balls. Upon and around this central pulp rests the hard tooth, 

 flattened out about the margin, consisting of Dentine {Substan- 

 tia ebiirnea) penetrated by its canals {Canaliculi dentium.^ 

 'These canals, raying out from the cavity of the pulp towards 

 the margin like a fan, open into that cavity, and contain, when 

 fresh, a yellowish fluid, but soon they become white by drying 

 and successive reception of air. They run out first in large, 

 simple canals, often a little undulated ; but soon they branch, 

 and the branches anastomosing with each other, form a net- 

 work of very fine capillaries. As this network does not reach 

 the periphery of the tooth, there remains a broad margin 

 entirely solid and transparent, like glass. This is the sharp 

 cutting edge. From the analogy with other teeth, and from a 

 view with a lower power of the microscope, one would suppose 

 that this transparent margin was an enamel crown extending 

 all over the tooth, but even with a very high power, I could 

 not find any trace of the characteristic polygonal fibres, and we 

 can state that this margin of the tooth is also composed of one 

 and the same homogeneous dentine, as the rest. 



There was no trace visible of either a blood-vessel or nerve 

 reaching into this pulp. With man and mammalia, this is 

 characteristic of a very old tooth ; but with this egg-tooth, 

 which is on the contrary very young, the drying of the nutri- 

 tive organs indicates nothing but their short duration. After 

 the drying and dying of those organs, and the consequent dry- 

 ing of the pulp and the fluid in the canals of the Dentine, the 

 tooth is only held mechanically in its socket, and being not 

 very deeply set, is rubbed ofi" by the first violent contact. This 

 process, of a sudden drying of life-imparting organs, is very 

 like that by which the horns of the deer are cast oif yearly. 



The short duration of this tooth, for it drops in one or two 

 days after the hatching of the snake, accounts for its havingbeen 

 overlooked by naturalists for so long a time. Even Rathke, in 

 his beautiful work on the evolution of the Ring Snake, published 

 in 1839, has made no mention of it, though lie describes very 



