970 SPECIAL PHYSIOLOGY. 



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According to Kolliker and others, however, the dental papillae, fol- 

 licles, and sacs, are formed entirely beneath the epithelium over the 

 jaw. The enamel organ is the part first developed, as a thickening of 

 the deeper layers of the epithelium, which grows down into a flask-shaped 

 depression, formed in the vascular layer or corium of the mucous mem- 

 brane ; the papilla then rises up as an extension from this membrane. 

 By removing the epithelium, the dental groove, follicles, and opercula, 

 of Goodsir are seen. 



The form of the summit of the papilla being completed within the 

 sac, a thin cap of dentine appears on it, which gradually increases at 

 its edges, and becomes thickened on its inner surface, whilst the 

 papilla, at first growing wider, but then contracting at its base to form 

 the cervix of the tooth, continues to grow longer, and commences to 

 form the fang, which shortly acquires its covering of crusta petrosa. 

 In the meantime, by a separate process, the surface of the cap of den- 

 tine, on the crown, becomes covered by the growing enamel, formed 

 from the enamel organ. At last, by the gradual growth of the fang, 

 the tooth is pressed against the gum, which, becoming absorbed, the 

 finished surface of the enamel is exposed, and the tooth is cut. The 

 fang is now completed to its point, and the papilla, now called the pulp, 

 remains as a vascular and nervous mass, occupying the pulp cavity, 

 and receiving its vessels and nerves through an orifice left at the apex. 

 In the meantime, the alveolus in the bone, has closely adapted itself 

 to the fang. 



In the growth of a tooth having several cusps and fangs, a separate 

 shell of dentine and enamel forms on each cusp, the whole afterwards 

 uniting ; whilst the dentine shoots in at opposite points of the base of 

 the pulp, where this begins to divide to form the separate fangs. 



Behind the growing milk teeth, in each jaw, recesses are formed in 

 the corium of the mucous membrane, which also become filled with 

 epithelium, out of which future enamel organs are developed. More- 

 over, a vascular papilla arises from the bottom of these flask-shaped 

 depressions or cavities of reserve (Goodsir), which finally close, and 

 become the sacs of a like number of the permanent teeth. These sacs 

 are at first oval, and adhere to the back of the sacs of the correspond- 

 ing milk teeth, but afterwards they become more elongated, and re- 

 cede from the gum, to which they are only attached by a fine cord or 

 pedicle, found behind the necks of the other teeth. In this way, in 

 Man, the ten anterior permanent teeth in each jaw, are developed. 

 But the sacs for the three additional or superadded permanent teeth, 

 on each side of the two jaws, viz., the sacs of the permanent molars, 

 are formed by little posterior cavities of reserve, which appear on the 

 edges of the jaws, behind the other teeth. These latter teeth are cut 

 like the milk teeth. But the anterior permanent teeth emerge differ- 

 ently. Between the fang of the temporary tooth, and the sac of the 

 corresponding permanent tooth, there is a thin layer of cancellated 

 osseous tissue; and in this bone, is a little canal, which lodges the 

 pedicle of the sac. The crown of a permanent tooth, being completed 

 within its sac, its fang or fangs begin to be formed; the crown is 

 pressed against the bony partition separating it from the fang of the 



