| OCR Text |
Show 472 MR. M. r. WOODWARD ON MAMMALIAN DENTITION. [May 2, V.-EXPLANATION OF PLATES XXXV.-XXXVII. In all cases the teeth represented are from the left side, and when shown in section are looked at from the front, so that the left of the Plate represents the inner side of the jaw. Fig. 1. Jaws of Petrogale (113 m m . long), clarified, and showing the tooth-germs in situ. iL-ia, the 6 upper incisors; i^-i^, the 3 lower incisors; c, canine; pm3, pm*, pm3, pm4, the upper and lower premolars; m1, mv the 1st upper aud lower molar; pms, the premaxillo-maxillary suture. 2. W a x model of the enamel-organs of the 1st and 2ud upper incisors; lettering as above, d.l, dental lamina ; f, rudiment of successional tooth. 3. Transverse section of the enamel-organs of tbe 3rd and 4th upper incisors of Petrogale. 4. A wax model showing the relation of the 4th upper incisor (f) to the 5th (i5) and 6th (ie). Petrogale. 5. Transverse section through the 5th (is) and 6th (i6) incisors of Macropus eugenii. i6', rudimentary successional tooth. 6. Transverse section through the upper 4th and 6th incisors (f and f) with the rudimentary successor to the latter (ie'). The vestigial 5th incisor (i5) is dotted in to show its relative position. M.giganteus. 7. Transverse section through the developing 1st incisor of M. giganteus. iu, successional tooth. 8. Transverse section through the enamel-organ of the 4th incisor and its rudimentary successor, i4'. M. giganteus. 9. Section taken parallel with the median plane of the head, but transverse to the dental lamina, passing through the 1st and 2nd lower incisors (ij and i2). Petrogale (95 cm.). 10. Enlarged drawing of the 1st lower incisor (t,), showing its advanced calcification and its rudimentary successor it'. Petrogale (11 cm.). 11. Transverse section through the 2nd lower incisor of M. giganteus. i2', rudimentary successor. 12. Section through the dental lamina between the canine and 3rd premolar, showing a slight differentiation, possibly representing one of the missing premolars. Petrogale. 13. Ditto. M. eugenii. 14. Section in front of the 3rd lower premolar, M. giganteus, showing the missing 2nd premolar. 15. Section through the enamel-organ of the 3rd premolar. Petrogale. 16. Section showing the earliest indication of the so-called 4th successional premolar (ppm). Petrogale (95 cm.). 166. Section through the same region as 16 a in an older embryo. 11 cm. 17. Section showing the character of the dental lamina between figs. 15 and 16 or 16 and 18. Petrogale. 18. Enamel-organ of the 4th premolar ; p possibly represents the last trace of a successional tooth. Petrogale. 19. A drawing of a wax model showing the relation between pm3 and pmx and the permanent premolar (jypm). Petrogale. 20. Section through the enamel-organ of the 3rd premolar of M.giganteus. 21. The dental lamina between pm3 and pm4, already slightly swollen, the earliest appearance of the successional tooth (ppm). M. giganteus. 22. The enamel-organ of the 4th premolar. M. giganteus. 23. Section through the 3rd premolar and the germ of the so-called 4th successional tooth (ppm). M. eugenii. 24. Ditto, ditto. JEpyprymnus rufescens. Showing the relation of the hitherto supposed successor (ppm) to the 4th premolar topm3 aud pm,. 9)1 9)1 25. a, b. The developing germs of - oi Petrogale. - , the milk-rudiments; m1' .m* m^ -,, the germs of the functional and permanent teeth. |
