FORMATION OF THE TEETH. 483 



" The operation is similar to the formation of the shell of the 

 egg, the stone in the kidneys and bladder, and the gall stone. 

 This accounts for the striated crystallized appearance which 

 the enamel has when broken, and also for the direction of these 

 strire. 



" The enamel is thicker at the. points and bases than at the 

 neck of the teeth, which may be easily accounted for from its 

 manner of formation; for if we suppose it to be always secreting 

 and laid equally over the whole surface, as the tooth grows, the 

 first formed will be the thickest; and the neck of the tooth, 

 which is the last formed part enclosed in this capsula, must 

 have the thinnest coat; and the fang where the periosteum 

 adheres, and leaves no vacant space, will have none of the 

 enamel. 



" At its first formation it is not very hard, for, by exposing 

 a very young tooth to the air, the enamel cracks and looks 

 rough; but 'by the time that the teeth cut the gum, the enamel 

 seems to be as hard as ever it is afterwards ; so that the air seems 

 to have no effect in hardening it." 



The preceding passages have been extracted literally from 

 Mr. J. Hunter's Natural History of the Human Teeth, not only 

 on account of their graphical value, but to fix upon him the 

 merit of having first considered the human teeth as a secretion ; 

 an opinion the originality of which is falsely attributed to the 

 Baron Cuvier, by M. Serres.* 



In infants, for several months after birth, the biting margins 

 of the gums upon each jaw are faced by a cartilaginous rising 

 of some lines in elevation,, and divided by slight fissures. Its 

 usual appellation is that of Dental Cartilage (Cartilago-Den- 

 talisi) it performs the function of teeth, in retaining the nipple, 

 and in mastication, and is analogous to the horny beak of birds, 

 and of some reptiles; it only disappears upon the protrusion of 

 the teeth. In the upper jaw it is about three lines wide, and 

 in the lower about two. If it be removed by thin slices, suc- 

 cessively made, till the margins of the alveoli appear, one 

 arrives by that means at the ends of the dental follicles or 

 sacs; from which it appears that there is no intermediate sub- 

 stance. 



* Anat. et Phys. des Dents, p. 63, 



