76 



CONNECTIVE TISSUES TEETH. 



sessing its characteristic lacunre and canaliculi. It is destitute, however, of 

 any lamellar structure. It is thickest at the extremity of the fang, and be- 

 comes gradually thinner towards the neck of the tooth, where it terminates. 



FIG. 36. 



Section through the fang of a Molar Tootli : n, a, dentine traversed by 

 its tubuli ; I, b, nodular layer ; c, c, ceuientum. 



FIG. 37. 



A. Transverse section of Enamel, showing the hexagonal form of its prisms; B, separated prisms. 



The following are the results of Von Bibra's analysis of the component 

 structures of human teeth : 



Organic matter, 

 Earthy matter, 



Incisors of Adult Man. 



Dentine. Enamel. 



. 2870 3.59 



71.80 96.41 



100.00 



100.00 



Cementuni. 

 29.27 



70.7.", 



100.00 



In tracing the development of the teeth, they are found to be essentially 

 dermal structures, which have undergone calcification, the epithelium form- 

 ing the enamel, and the mucous tissue the dentine and cement. At the 

 sixth week of foetal life a deep, narrow groove may be perceived in the 

 upper jaw of the human embryo, between the lip and the rudimentary 

 palate. This is speedily divided into two by a ridge, which afterwards be- 

 comes the external alveolar process; and it is in the inner groove, which is 

 termed the primitive dental groove, that the germs of the teeth subsequently 

 appear. The groove is at first completely covered and filled with the epi- 

 thelium of the oral cavity, so that on a surface view it is scarcely percepti- 

 ble. From the bottom of the dental groove a narrow process of the oral 



