TEETH. 



[ 634 ] 



TEETH. 



then formed, and approaching each other. 

 Fig. 742. 



Lower jaw of a human nine months' foetus, a, tongue, 

 turned back ; b, right half of the lower lip turned aside ; 

 b', left half of the lip cut off; c, outer Mall of the gura ; 

 d, inner wall of the gum ; e,f, g, h, papillae of the teeth ; 

 i, fold where the sublingual duct subsequently opens. 



Magnified 9 diameters. 



enclose the papillae in distinct follicles, the 

 margins of which gradually grow over the 

 papillae, and uniting, convert them into 

 closed sacs or capsules. The pulps then 

 become moulded into the form of the future 



teeth ; the bases of the pulps dividing into 

 as many portions as the teeth have fangs, 

 and as the capsules increase at this stage 

 faster than the pulps, a space is left between 

 them, in which a gelatinous-looking sub- 

 stance is deposited from the wall of the 

 capsule forming the enamel organ. 



The capsule (fig. 743 a) possesses an 

 areolar coat with vessels and nerves, and 

 from its base arises the tooth-germ or pulp 

 (fig. 743 h). The pulp consists of an outer 

 non-vascular layer of elongated, nucleated 

 cells, with filiform processes, in close appo- 

 sition (fig. 744 a), covering the surface of 



Capsule of the second incisor tooth of an eight months' 

 human foetus, a, capsule ; b, enamel-pulp ; c, enamel- 

 membrane ; d, enamel; /, ivory cells ; h, papilla of tooth 

 or pulp ; i, free margin of enamel-organ. 



Magnified 7 diameters. 



Surface of the pulp of a newly-born infant, a, wing- 

 cells ; b, their appendages ; c, vascular part of the pulp. 



Magnified 300 diameters. 



the pulp, the ivory-membrane (fig. 743/), 

 not distinctly defined internally, but gradu- 

 ally passing into the vascular parenchyma of 

 the pulp. The inner part of the pulp con- 

 sists of indistuictly fibrous areolar tissue 

 with nuclei ; the vessels terminating in loops 

 beneath the enamel membrane (fig. 744 c). 



The enamel organ (fig. 743 b) covers, by its 

 inner concave surface, the pulp, its outside 

 being in apposition with the capsule. It 

 forms a spongy tissue, composed of anasto- 

 mosing stellate cells or reticular areolar 

 tissue; in its inside is the enamel membrane, 

 consisting of cylindrical epithelium (fig. 

 743 c). _ 



Ossification commences by the deposition 

 of calcareous matter in the cells of the ivory 

 membrane at the summit of the pulp ; this 

 is soon followed by similar deposition in the 

 cells of the enamel membrane. Bv the 



