240 ON THE DEVELOPMENT OF THE TEETH 



DESCRIPTION OF PLATE III [XXIH.]. 



The letters refer throughout to the same or corresponding parts. 



a. The JIucous Membrane of the mouth. 



i. The Lip. 



('. The Alveolus. 



d. The Pulp. 



e. The Dentine. 

 /. The Enamel. 



^. The Basement Membrane of the Pulp. 

 g:^ Xasmyth's Membrane especially. 

 /;. The " Enamel-organ " or Epithelium of the Capsule. 



!. The Basement Membrane of i the Capsule, with its subjacent condensed tunic. 

 Hunter's inner, vascular, capsule. 



/!■. The loose submucous cellular Tunic. Hunter's outer, non-vascular, capsule. 



Fig. I. Diagrammatic section of the inner incisor of the upper jaw of a Seven-months 

 Foetus. The loose enamel organ is indicated by * * * *. 



Fig. 2. A cusp of the posterior molar, upper jaw of the same. The inner outline 

 represents it before the addition of acetic acid — the outer afterwards, «'hen Nasmyth's 

 membrane is seen raised up into large folds. 



Fig. 3. Edge of an incisor pulp — retaining its cap — not far from the lower edge of the 

 dentine, which was about i- 1600th of an inch thick. 



Fig. 4. Edge of the pulp of a molar cusp, showing the first rudiment of the dentine, 

 commencing in a perfectly transparent layer between the "nuclei" of the pulp and the 

 membrana preformativa. 



Fig. 5. Surface of this dentine, where it had attained a thickness of i-25ooth of an inch, 

 before which the little cavities, if present, were not visible. 



Fig. 6, Nasmyth's membrane detached from the sirbjacent enamel by acetic acid. 



Fig. 7. The "stellate-cells" of the human "enamel-organ." 



Fig. 8. Tooth of the Frog, acted on by dilute hydrochloric acid, so as to dissolve the 

 enamel and free Nasmyth's membrane. The structure of the dentine is rendered indistinct. 

 At the base Xasmyth's membrane is continued over the bony substance at j, in which the 

 nuclei of the lacunte are visible. 



Fig. 9. Extremity of the tooth of a Mackerel, acted on by hydrochloric acid so as to 

 dissolve the enamel. Nasmyth's membrane is rendered obvious, but is burst on the left-hand 

 edge. 



Fig. 10. Tooth-sac of a Mackerel, i-50th of an inch long, extracted from its alveolus. Its 

 close resemblance to a hair-sac is very striking. 



Fig. II. Diagrammatic section of the dental follicles of a Skate, to show the union of the 

 upper and lower folds of the " dental groove." 



Fig. 12. Extremity of a dermic, tooth-like spine, from the upper surface of the head in 

 the Skate, acted on by hydrochloric acid, which has removed the layer of enamel. 



