212 H. SPENCER HARRISON. 



nation in the maxillary aud the less marked one in the mandibular teeth. 

 Palatine teeth not shown. X 5. 



Pig. 12. — Section of a lower tooth of the first series at Stage S. T. 1. Tooth 

 of first series, ep. s. Capsule of flattened cells. (S. 2. x 240.) 



Fig. 13. — Section of palate passing through the enamel organ of the 

 vomerine tooth of left side. Vo. Vomer. V. e. o. Enamel organ. (S. 

 Sagital. X 240.) 



Fig. 14. — Section of mandibular tooth, with bone of jaw. In this section 

 are also figured the labio-dental groove {I. d. gr.), formed from the corre- 

 sponding strand of cells by splitting ; also the mandibular dental fossa, formed 

 in the same way from the lingual ingrowth, cutting off a ridge of mucous 

 membrane (with a core of mesoderm), which runs between the inner face of 

 the jaw aud teeth and the tongue (cf. also figs. 5, 8, 19). The glands on the 

 sides of the grooves and on the lower lip [1. 1.), together with the shelf of the 

 latter, are shown. The enamel of tiie tooth has been removed in the process 

 of preparation. At the base of the internal dental fossa a solid ridge of 

 epithelial cells (r.d.l.) remains non-glandular, and no doubt represents the 

 deutal lamina, which has been carried down by the glandular ingrowth (cf. 

 figs. 19, r.d. L, and 18, L s.^). (Embryo S, 19a, Frontal section. X 60.) 



Fig. 15. — Section of junction of tooth and bone at Stage S. On its 

 internal surface the dentine has a more recently formed layer (unshaded). 

 On the labial side the close attachment of the epithelium to the tooth and 

 bone is shown, b. c. Bone-corpuscles, ep. gr. Epithelium of inner limb of 

 labio-dental groove. (S, 19a. Frontal section, x 240.) 



Fig. 16. — Sagittal section through posterior part of right upper and lower 

 jaws at Stage S, to show the posterior continuation of the dental laminae of 

 maxilla and dentary. Three large teeth have been cut through, and one small 

 one on the upper dental lamina, e. o.f. Enamel organ of tooth of alternating 

 series. (S 2. Sagittal, x 60.) 



Fig. 17. — Anterior view of premaxillary and anterior mandibular teeth at 

 Stage T, to show the relative reduction in size of the second premaxillary on 

 each side. X 5. 



Fig. 18. — Sagittal section through the second premaxillary tooth of one 

 side, to show the development of a successional tooth, which arises from the 

 epithelium near the deepest part of the internal dental fossa {lin.gr'.). The 

 glandular portion of the latter is not evident, and the labial side of the 

 section is damaged. The functional tooth is seen to be attached to the bone 

 on the labial side only. jmix. t. Second premaxillary tooth, t. s. 1. First 

 successional tooth. (Stage T. Sagittal section. X 60.) 



Fig. 19. — Section through third mandibular tooth of one side, showing a 

 well-defined mass of epithelial cells at the base of the internal dental fossa. 

 The interpretation of this as a dental lamina is justified by the formation of 



