18 MICROSCOPIC ANATOMY OF THE TEETH 



chiefly on the outer side of the wall of the jaw, but in the 

 incisor region, on the top of the jaw wall. As Rose says : 

 ' This tooth furrow (which, as already mentioned, indicates 

 the line of demarcation of the tooth-band from the epithelium 

 of the jaw) is in some places fairly deep, in others scarcely 

 indicated, in places even, obviously double, according to 

 the more or less irregular disposition of the tooth-band.' 

 Rose's Rose prepared a series of wax models built up by the 



B s< ingenious method of Born, which show the important points 

 in this explanation of the mode of development of the teeth, 

 which is now generally accepted as being in most particulars 

 the correct one. 



FIG. 2. From the model of the mandible of an embryo of nine weeks. 

 a. tooth- band ; 6. lip furrow band ; c. lip furrow. 



These models are made to scale, from photographs of 

 serial sections, magnified to the same degree and copied on 

 sheets of wax, which are moulded into a solid model by 

 melting their edges. 



Three of these models are figured in the accompanying 

 illustrations, and a description of them may assist in obtain- 

 ing a clear understanding of the most important points in 

 mammalian tooth development. 



Fig. 2 shows a photograph of the model of the epithelial 

 surface of the mandible of an embryo of nine weeks, 2-5 cm. 

 in length. The opening of the mouth is represented with 

 part of the epithelium of the lip and of the mucous mem- 

 brane of the mouth. The tooth-band is seen as a curved 

 band directed backwards ; in the mandible at this stage it 

 shows an undulating margin and enlargements at intervals, 



