THE DEVELOPMENT OF THE TEETH. 171 



their way through it, substituting for the calcined cartilage 

 a bone developed from osteoblasts, and ultimately all remains 

 of the calcined cartilage or temporary bone disappear. Thus 

 all bone whether developed in cartilage or in membrane 

 is formed alike, the calcined cartilage merely forming a 

 temporary framework or scaffolding, in and amongst which 

 the bone is formed from osteoblasts. But M. Magitot does 

 not describe in much detail this calcification of cartilage and 

 subsequent removal to give place to an osteoblast-derived 

 bone, though he speaks of the cartilaginous cement organ 

 as a transitory or temporary structure. 



Membrana Preformativa. To the student of dental 

 development few things are more perplexing than the con- 

 flicting statements which he reads in various works as to 

 the nature and position of the Membrana preformativa, of 

 which I have hitherto studiously avoided all description; 

 while it is not encouraging, after having mastered with 

 difficulty some one description of its character, to find that 

 many of the most recent authors altogether deny its exist- 

 ence. I will endeavour, therefore, so far as I am able, 

 although not myself believing in its presence, to put the 

 matter in a clearer light, and to point out wherein lie the 

 discrepancies of statement. 



According to the older theories of tooth development, 

 under the thrall of which most authors have written, the 

 tooth germ was in the first instance a free, uncovered papilla 

 of the mucous membrane, which subsequently sank in and 

 became encapsulated, &c., &c., (see page 129). Moreover, it 

 was taught by the older histologists that fine homogeneous 

 " basement membranes " were to be found in a great variety 

 of situations, amongst others beneath the epithelium of the 

 mucous membrane, and that these were of (physiologically) 

 much importance, inasmuch as they formed defining limits, 

 through which structures did not pass. As a necessary con- 

 sequence of these views, it was assumed as a matter of 



