OF THE NEWT, FEOGr, SLOWWOEM, AND GEEEN LIZAED. 
295 
formation in the newt sends up its branching fibres through the epithelium, reaching 
almost to its surface (Plate 46. figs. 2, 3, 5), renders it difficult to suppose that a base- 
ment membrane intervenes between it and the epithelium. But there is no such diffi- 
culty in the case of the frog, in which animal the boundary-line of the epithelium is less 
irregular ; and it must be admitted that there is an a priori probability in the enamel- 
germ being enclosed within a basement membrane, if this exists between the oral epithe- 
lium and the subjacent tissues ; so that I am unable to speak more positively than to say 
that I have uniformly failed in demonstrating the existence of such a membrane. 
Explanation of the Plates. 
PLATE 46. 
a. Tooth-bearing process of maxillary bone. 
b. Oral epithelium. 
c. Neck of epithelial cells connecting the tooth-sac with the oral epithelium. 
d. Young tooth-sac. 
e. Dense connective tissue, forming the internal limit to the area of tooth-formation. 
f. fi- Processes of epithelium (= enamel-germs of Kolliker) which will ultimately 
participate in forming tooth-sacs. 
h. Formative pulp of the dentine. 
k. Cap of dentine. 
l. Columnar epithelium of the enamel-organ (enamel cells). 
m. Connective-tissue band on the outer side of the area of tooth-formation. 
o. Odontoblast layer of dentinal pulp. 
t. Completed tooth. 
Figs. 1 to 9. From the upper jaw of Triton cristatus. 
Fig. 1. From newt half-grown, x 50. 
Fig. 2. From newt half-grown (the lip is omitted from this figure), X 50. 
Fig. 3. From adult specimen. Teeth in four stages of development are seen within the 
area, X 50. 
Fig. 4. Young tooth-sac in which the cap of dentine is just formed, X 120. 
Fig. 5. Young tooth, showing its relations with the oral epithelium and with the 
successional enamel-germ, X 200. 
Fig. 6. Termination of epithelial process, commencing to form the enamel-organ of a very 
young tooth-sac, x 220. 
Fig. 7. Young tooth-sac, viewed on its surface, which is seen to be a tesselated epithe- 
lium, x 220. 
Fig. 8. Very young tooth-sac, showing odontoblast layer. 
2 r 2 
