594 ON MAMMAWAN DENTITION. [May 5," 



■ Figa. 10-14. Gymnura. 

 Fig. 10. Developing 3rd upper incisor (pi. 3) with calcified vestigial milk 



predecessor (di, 3), 

 , 11. Germ of 2iid upper premolar (ppm. 2) with reduced mills predecessor 

 (dpvi. 2). 



12. Germ of ;ind lower premolar (ppin. 2), milk predecessor {dpm. 2) still 



more reduced. 



13. Upper jaw of (?^TOn«ra showing milk dentition and cavities occupied by 



germs of permanent teeth, w.l, first molar ; (ipjn. 2, 2ad 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), lingual growth of dental lamina 

 (d.l.)._ 



16. Germ ot pi. 2 with labial vestigial milk predecessor (di. 2). 



17. Ditto, pi. 3 ; ditto, di. 3. 



18. Ditto, permanent canine, pu. (i. 4) ; ditto, dc. 



19. Flan 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 oi pi. 3 and di. 3 (vestigial). 



22. Ditto of ppm. 3 and dpm. 3 (vestigial). 



23. Ditto o{ ppm. 4 and dpm. 4 (vostigial), 



24. Ditto oi'ppm. 4 and dpm. 4 (vestigial). 



Figs. 25-26. Centetes. 

 Fig. 26. Germof»\3. 



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 laniinu ; 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 do., dpm. 1, dpm. 2, dpm. 3, and those of their successors 

 in the permanent series, pc. very advanced ; ppvi. 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 of 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 »n. 1, showing the 



primitive dentine germ giving rise to the paracone (5), and the first 



trace of the protocone (7), also a very prominent swollen lingual 



development of the dental lamina. 

 Fig. 33. (a) palatal, (4) external aspect of an upper molar (m.) tooth otPeralestes, 



34. DiUo, ditto o{ Centotes (m.l). 



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. 



