940 



THE ORGANS OF DIGESTION. 



enamel-forming layer (Figs. 565 and 566). The cells of the outer wall remain 

 cuboidal ; the cells which lie between become much distended, and on account of 



FIG. 561 Diagram of method of development of the teeth. 1. Early stage. 4. Later stage. 2, 3. Interme- 

 diate stages, s. Common dental germ. o. Special dental germ (milk), o'. Special " 



p. Papilla, e. Dental furrow. (Gegenbaur.) 



ial dental germ (permanent). 



their appearance when seen in section this portion of the organ is called the stellate 

 reticulum (the enamel-jelly). The layer of cells immediately contiguous to the 

 ameloblasts form a layer called the stratum intermedium (Fig. 566A D). 



The enclosed mesoblastic papilla (the future dental pulp) has its peripheral cells 

 differentiated into columnar bodies disposed as a layer, each cell having a large 



Dental furrow 



Remains of ' ' neck " of 

 enamel organ, or of the 

 common dental germ 



Permanent special 

 dental germ 



MeckeVs cartilage. 



Internal enamel layer, 

 or adamantoblasts 



Dental sac 



lamel pulp 

 External enamel 

 layer 

 Papilla 



Lower jaw. 



FIG. 565. Vertical section of the inferior maxilla of an early human foetus. (Magnified 25 diameters.) 



nucleus. The vascular supply of the pulp is now well marked. A section of a 

 follicle at this period will exhibit the follicular wall springing from the base of the 

 dental papilla and having a well-marked blood-supply. The bony alveolar walls 

 are well outlined, and evidences of a periosteum appear (Figs. 565 and 566). 



Development of Enamel. In point of time, the deposition of dentine actually 

 begins before that of enamel, so that the first-formed layer of enamel is deposited 

 against a layer of immature dentine. The enamel is built up of two distinct sub- 

 stances globules of uniform size which are formed by the ameloblasts, and a 

 cementing substance, probably an albuminate of calcium (calco-globulin), the basis 

 of all the calcified tissues. At the ends of the ameloblasts, next to the dentine, 

 the secretion calco-globulin is deposited, and into the plastic mass the enamel- 

 globules are extruded, each globule remaining connected with the ameloblasts by 

 plasmic strings, which also join the globules laterally. 1 



The first deposit of enamel begins in the tips of the cusps, and is quickly fol- 

 lowed by a disappearance of the stellate reticulum at that point ; the stellate retic- 

 ulum now appears to atrophy, so that the vascular follicular wall is brought into 

 direct apposition with the stratum intermedium, which becomes differentiated into a 

 glandular (secreting) tissue which elaborates the calcic albuminous basis of the 

 enamel. The secretion passes from the cells of the stratum intermedium through a 

 membrane into the ameloblasts, where it is in part combined with the cellular 



1 J. L. Williams, Dental Cosmos, 1896. 



