106 



MANUAL OF HISTOLOGY. 



membrane, which in consequence of chemical and histological 

 conversion of its constituents has acquired a remarkable degree 

 of hardness, and according to whether the connective-tissue 

 substance of the papilla participates in the hardening or not, 

 two large groups of teeth are distinguished dentinal teeth and 

 horny teeth. The horny teeth are by far the most simple in 



Fio. 40. Vertical section of the Inferior maxilla of a hu- 

 man foetus,meuBuring 11 ctms. from the vertex to the coccyx. 

 Magnified 25 diameters. 1, dental groove; 2, remains of the 

 enamel germ ; 3, enamel organ presenting externally epitheli- 

 um, as also where it forms the enamel germ of the papillae of 

 the dental sacculus ; 4, secondary enamel germ : rudiment of 

 the permanent tooth ; 5, dental germ : 6, lower jaw ; 7, 

 Meeker B cartilage. (VValdeyer.) 



Fio. 41. 1, various forma of 

 odontoblasts, with the three kinds 

 of processes;, 2. three enamel 

 cells, with a few cells of the stra- 

 tum intermedium attached ; 3, an 

 enamel cell, with a small portion 

 of enamel ; 4, fragments of ena- 

 mel fibres from young and soft 

 enamel ; 5, old '.-namel fibres with 

 transverse rtrise and rounded ex- 

 tremities. (Wuldeyer.) 



their structure. They appear as more or less developed papil- 

 lae covered with a thick horny investment. They are never 

 continuous with portions of the skeleton, but constitute the 

 transition to other horny formations, as hairs, stings, etc." 



" In the dentinal teeth the connective-tissue matrix of the 

 papillsB plays a most important part in the hardening process, 

 which here proceeds in a manner precisely similar to the ossi- 

 fying process, except that no true bone is formed, but only an 

 allied substance, of much harder consistence, and differing 

 more or less in histological structure, termed dentine. The epi- 

 thelium of the tooth papillae either atrophies to a rudimentary 



