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MANUAL OF HISTOLOGY 



27-61 

 0-40 



6672 

 3-36 

 1-08 

 0-83 



20-42 

 0-58 



67-54 

 7-97 

 2-49 

 1-00 



71 to 78 per cent., while the collagenic substratum of the tissue (the so- 

 called tooth cartilage) ranges about from 20 to 29 per cent. 



The following two analyses of Bibra may be taken as an example. 

 They refer to the dried dentine of human molar teeth. The first of these 

 was from an adult male ; the latter from a woman twenty-five years of age. 



Organic collagenic substratum, 



Fat, . 



Phosph. and fluoride of calcium. 



Garb, of calcium, . 



Phosph. of magnesium, .. 



Other salts, . 



As to the softer crusta petrosa, any distinction from dentine is doubt- 

 ful. The investigations which have taken place up to the present show 

 somewhat more organic substratum yielding glutin. Its nature is other- 

 wise similar to that of dentine. Bibra obtained from that of the human 

 teeth, 29-42 (inclusive of some fat) of organic substance, and 70*58 of 

 mineral constituents. 



153. 



The development of the teeth (1), as productions of mucous membrane, 

 is, even in its coarser outlines, a most difficult chapter in embryology. 



From the fourth month on of 

 intra-uterine life, we remark in 

 the human embryo preparation 

 for the formation of the future 

 milk-teeth. This takes place on 

 the edges of the jaws, by the 

 formation of closed follicles, from 

 the floor of which a papilla pro- 

 jects into the cavity, destined to 

 produce the dentine of the struc- 

 ture, and, moreover, in the first 

 place, that of the crown, while 

 the remainder enters into the 

 formation of the pulp. These 

 papillary structures, which re- 

 semble in form the crown of 

 the future tooth, are called the 

 " ' tooth' or ' dental ' germs." 



In fig. 256 we have a sketch 

 of one of these follicles from a 

 tolerably mature embryo, with 

 its but ill-defined wall of con- 

 nective-tissue (a) and dental 

 germ (/) containing numerous 

 capillaries (g). The latter is 

 covered by a peculiar structure, 

 in the form of a cap, hanging down over its sides (b). This has been 

 named the " enamel-organ," on account of its presiding over the produc- 

 tion of the enamel, as we shall see presently. Its concave inferior surface 

 is lined by a layer of narrow cylindrical cells (d) covering the dental 



Fig. 256. Dental sac of a human embryo at an ad 

 vanced stage of development, partly diagrammatic. 

 a, -wall of the latter, formed of connective-tissue, and 

 with its outer stratum a 1 , and inner a 2 ; 6, enamel 

 organ with its papillary and parietal layers of cells c; 

 d, the enamel membrane and enamel prisms; e, 

 dentine cells; /, dental germ, and capillaries g; 

 i, transition of the connective-tissue of the wall of 

 the follicle into the tissue of the dental germ. 



