DEVELOPMENT OF THE TEETH IN MAMMALIA 19 



the enlargements being the first indication of the separation 7 

 of the original enamel organs. 1 



Fig. 3 is a photograph of the model of the maxilla of 

 an embryo, fourteen weeks old, 11^- cm. in length. The 

 epithelial structures only are seen, looking down upon the 

 upper or cranial aspect of the epithelium of the mouth and 

 into the hollow caps of the epithelial enamel organs, which 

 are advancing in a vertical direction towards the observer, 



FIG. 3. From the model of the maxilla of an embryo of fourteen weeks. 

 The epithelial structures viewed from above. The germs of the ten deci- 

 duous teeth are seen. d. lip furrow ; c. lip furrow band ; 6. tooth germ ; 

 a. tooth-band ; of. prolongation of tooth-band to form permanent teeth. 



the free margin of the tooth-band also advancing upwards 

 behind and beyond the enamel organs. 



These enamel germs have been aptly compared to swallows' 

 nests attached to the flat surface of a board ; they are seen 

 to be attached to the labial surface of the tooth-band and 

 not to its free growing margin. The mesodermic tissues are 

 not represented in the model, being supposed to be stripped 

 off from the epithelial structures. 



1 A set of these models is to be seen in the Odontological section of the 

 Hunterian Museum of the Royal College of Surgeons. Details of the mode 

 of production of the models are given in Rose's original paper (19) and 

 in the author's communication to the Odontological Society's Trans., 

 May 1893. 



C 2 



