1216 



THE ORGANS OF DIGESTION 



tissue beneath. The mesoderm at the base of each enamel organ condenses, and seems to 

 force the adjacent part of the enamel germ toward the apex of the organ, producing thus a sac- 

 like structure, the enamel organ; the latter now consists of three layers, outer columnar layer, 

 middle, stellate reticulum, and inner, enamel-forming cells, the membrana adamantina. The 

 papilla-like mass of mesoderm that extends into the enamel organ is called the dental papilla. 



Dental furrow 



Remains of "neck " of 

 enamel organ, or of the 

 common dental shelf 



Permanent special 

 dental germ 



Meckel 1 s cartilage. 



Internal enamel layer, 

 or adamantoblasts 



Dental sac 



Enamel pulp 



f~ External enamel 

 layer 

 Papilla 



Ifandible 



FIG. 933. Vertical section of the mandible of an early human fetus. (Magnified 25 diameters.) 



The mesoderm peripheral to the enamel organ condenses to form a sheath called the dental sac 

 or follicle. In the meantime the dental shelf becomes attenuated and tends to disappear, and 

 bone is being deposited in the intervals around and between the teeth, so that the latter soon lie 

 in a gutter of bone. 



The cells of the enamel organ now undergo a series of differentiations. The inner layer, 

 arranged as columnar epithelium, are the enamel cells, or ameloblasts. The layer is called the 



Dentine Enamel 



FIG. 934. Section through tooth follicle 

 human canine seven and one-half months. 

 A. Follicular wall. B. Outer epithelial coat. 

 C. Stellate reticulum. D. Stratum inter- 

 medium. E. Ameloblasts. F. Odonto- 

 blasts. G. Pulp. 



FIG. 935. Diagram after Williams (Dental Cosmos, 1896), 

 mode of enamel deposition. A . Blood supply to B, secreting 

 papillae. C. Layer of ameloblasts containing enamel 

 globules and droplets of calcoglobulin. D. Enamel globules 

 deposited. E. Formed dentine. F. Forming dentine. G. 

 Layer of odontoblasts. //. Blood supply to odontoblastic 

 layer. 



ameloblastic or enamel-forming layer (Figs. 934, 935, and 936). The cells of the outer wall 

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

 appearance when seen in section this portion of the organ is called the enamel jelly or the 

 stellate reticulum. The layer of cells immediately contiguous to the ameloblasts form a layer 

 called the stratum intermedium (Fig. 934, D). 



