TEETH. 321 



teeth, and which together constitute the secondary dentinal 

 groove.* 



Having now obtained a general idea of the development of 

 the teeth, we shall be prepared to understand the mode of 

 development of the individual tissues of the teeth, a subject 

 which has been studied more particularly by Mr. Nasmyth, 

 Professor Owen, and Mr. Tomes. 



Formation of the Dentine. It would appear to be a uni- 

 versal law of development that all animal and vegetable 

 tissues should take their origin in cells ; of this law the teeth 

 present a striking and beautiful example. 



Thus the dentine is formed out of the cells placed on the 

 formative surface of the papilla or dentine pulp. This view 

 of the formation of the dentine originated with Mr. Na- 

 smyth f, and its accuracy has been confirmed by the investi- 

 gations of subsequent writers, and especially by those of 

 Professor Owen and Mr. Tomes. 



Mr. Owen, in his work " Odontography," describes with 

 great minuteness the several steps of the conversion of the 

 cells of the pulp into dentine, and also enters upon the 

 consideration of the development of the other tissues of the 

 teeth. 



According to Mr. Owen, the cells of the pulp, which are 

 larger and more numerous on the surface, become arranged 

 in lines which are placed vertical to that surface ; subse- 

 quent to this arrangement the nuclei are seen to divide, first 



* For further particulars relating to the general development of the 

 teeth consult the admirable paper of Mr. Goodsir, contained in the 

 Edinburgh Medical and Surgical Journal. From the researches of that 

 gentleman we learn that the papillae of the teeth appear in the upper 

 jaw before the lower ; that those of the milk teeth are developed in three 

 distinct divisions, a molar, a canine, and an incisor ; that the molar is 

 the first formed, the canine the second, and the incisor the third ; also 

 that the first molar is developed before the second, and the first incisor 

 before the second. In the permanent teeth the papillae, with the excep- 

 tion of the anterior molar, appear at the mesial line first, and proceed 

 backwards. 



f Memoir on the Development and Organisation of the Dental Tissues 

 by Alexander Nasmyth, August, 1836. 



