| OCR Text |
Show 594 ON MAMMALIAN DENTITION. [May 5^ Figs. 10-14. Gymnura. Fig. 10. Developing 3rd upper incisor (pi. 3) with calcified vestigial milk predecessor (di. 3), 11. Germ of 2nd upper premolar (ppm. 2) with reduced milk predecessor (dpm. 2). 12. Germ of i!nd lower premolar (ppm. 2), milk predecessor (dpm. 2) still more reduced. 13. Upper jaw of Gymnura. showing milk dentition and cavities occupied by germs of permanent teeth, m. 1, first molar ; dpm.2, 2nd deciduous premolar. 14. Germ of dpm. 3 and ppm. 3, the latter just appearing. PLATE XXV. Figs. 15-24. Sorex. Fig. 15. Developing 1st lower incisor (pi. 1), Ungual growth of dental lamina (d.l.). 16. Germ of pi. 2 with labial vestigial milk predecessor (di. 2). 17. Ditto, pi. 3 ; ditto, di. 3. 18. Ditto, permanent canine, pc (i. 4); ditto, dc. 19. Plan of enamel germs of upper teeth in relation to the dental lamina and to the jaw-bones (pmx. and mx.). 20. Germ of pi. 2 with labial vestigial milk predecessor (di. 2). 21. Ditto ot pi. 3 and di. 3 (vestigial). 22. Ditto of ppm. 3 and dpm. 3 (vestigial). 23. Ditto ot ppm. 4 and dpm. 4 (vestigial). 24. Ditto ot ppm. 4 and dpm. 4 (vestigial). Figs. 25-26. Centetes. Fig. 25. Germ of 13. 26. Germ of m. 1, showing specialization of lingually placed dental lamina (d.l.). PLATE XXVI. Figs. 27-32. Talpa. Fig. 27. Horizontal section of the upper jaw, showing the tooth germs in relation to the dental lamina ; the milk-teeth are well developed, while the germs of the permanent teeth are just visible as swellings of the dental lamina. 28. Enlarged drawing of a deep horizontal section passing through the germs of dc, dpm. 1, dpm.2, dpm. 3, and those of their successors in the permanent series, pc very advanced; ppm. 1 transitory, never becoming more developed. 29. Clarified jaw of a very young Mole (hairless), showing the milk and permanent dentitions in situ. 30. Frontal section of a specimen about the same age as the last, showing dpm. 2 well calcified and the germ ot ppm. 2. 31. Ditto, ditto, passing through the first premolar (dpm. 1), showing last trace of the lingual dental lamina (d.l.). 32. Ditto of a young stage, passing through the germ of m. 1, showing the primitive dentine germ giving rise to the paracone (0), and the first trace of the protocone (7), also a very prominent swollen lingual development of the dental lamina. Fig. 33. (a) palatal, (b) external aspect of an upper molar (m.) tooth of Peralestes. 34. Ditto, ditto of Centetes (m.\). 35. Ditto, ditto of Talpa (m. 2). 36. Ditto, ditto of Chrysochloris (m.). The numerals attached to the last 4 figures represent an attempt to homologize the cusps. |
