THE DENTAL TISSUES OF THE ORDER RODENTIA. 
565 
Fig*. 21. A longitudinal section of a lower incisor of Myoxus avellanarius, showing at 
E the decussation of the parallel layers of enamel fibres, and the downward 
direction of the external ends. 
Fig. 22. A transverse section of the same tooth, showing the outward course of the 
enamel lamelise, their serrated margins near the dentine, and their vertical 
position. 
Fig. 23. A vertical section from the upper incisor of a Jerboa {Dipus ^gyptius), 
showing,©, the dentine at its anterior peripheral surface, and E, the enamel 
with a few tubes continued into the outer part. 150 linear. 
Fig. 24. An oblique longitudinal section, showing enamel fibres divided transversely 
and longitudinally. 300 linear. 
Fig. 25. A transverse section of an upper incisor of the Jerboa, showing,©, the den- 
tine, and E, the enamel, with the decussation of the fibres of contiguous 
layers in the lamelliform portion of the tissue, and their parallel course in 
the outer part of the enamel. 150 linear. 
Fig. 26. A longitudinal section of a lower incisor of the Jerboa from near the base of 
the tooth, showing, ©, the dentine, and E, the enamel, with the lamellae 
arranged in the length of the tooth. 150 linear. 
Fig. 27 . Enamel fibres scraped from the partially calcified tissue near the base of the 
tooth. 600 linear. 
Fig. 28. A transverse section of a lower incisor of the Jerboa, showing the enamel 
lamellae divided transversely with the fibres of alternate layers cut ob- 
liquely, and the intervening one longitudinally. 
Fig. 29. Plate XLV. A longitudinal section of a molar of the Jerboa, showing the 
periphery of the dentine and the dentinal tubes continued into the enamel, 
with the manner of termination of the tubes in the latter texture. 
Fig. 30. A longitudinal section of a lower incisor of a Rat {Mus decumanus), showing, 
©,the terminal portion of the dentine, and E, the enamel, with its serrated 
lamellae and its outer fibrous portion. 300 linear. 
Fig. 31. An oblique transverse section from the same tooth, showing the crossing of 
the fibres of contiguous layers, and the pattern thus produced. 300 linear. 
Fig. 32. A section from the same tooth, in which the fibres of alternate layers are 
divided transversely, and tlie intermediate ones exposed in their length, 
and show minute denticulations. 
Fig. 33. Enamel fibres in various stages of development, obtained from the partially 
calcified tissue about the base of the incisor. 
Fig. 34. A longitudinal section from a lower incisor of the Bank Vole {Arvicola gla- 
reo/iM'), showing at E the denticulated character of the enamel larnellse and 
their transverse markings. 
