THE DENTAL TISSUES OF THE ORDER RODENTIA. 
563 
Explanation of the Figures, in eacii of which D refers to the dentine, 
and E to the enamel. 
PLATE XLIIL 
Fig. 1. The middle portion of a transverse section of the lower incisor of Tamlas 
Lysteri, showing the manner in which the dentinal tubes are disconnected 
from the pulp-cavity in that part of the tooth which is about to come into 
wear by the development of a laminated subgranular tissue. 150 linear. 
Fig. 2. A transverse section of a dentinal system. A, and peripheral portion of two 
contiguous ones, B and C, from the tooth of Orycteropus, showing the 
manner in which the connection of the dentinal tubes with the surface of 
the pulp-cavity is cut off by the development of a laminated mass of trans- 
parent and apparently structureless tissue. 
Fig. 3. A transverse section of a dentinal system. A, and a portion of a contiguous 
one, B, from the tooth of Lahyrinthodon Jaegeri, showing the disconnection 
of the tubes with the pulp-cavity in A, and the process, C, by which this is 
connected with a contiguous system ; also the peripheral line of cells which 
intervene and partially connect the terminal branches of the tubes of ad- 
joining systems. (This drawing was made from a section, No. 4 of a series 
lent to me by Dr. Mantell.) 75 linear. 
Fig. 4. A transverse section of a Havei’sian system from a Stag’s antler which had 
been cast, showing the transparent tissue lining the canal, and thus cutting- 
off the connection of the canaliculi with the surface of the canal. 
Fig. 5. A transverse section from the extruded portion of a molar tooth of Lepus 
timidus, showing that the medullary canals of vascular dentine become 
lined with a dense non-tubular tissue previous to the part coming into 
wear. 
Fig. 6. A portion of a longitudinal section from an upper incisor of Sciurus niger, 
showing, D, the dentine, E, the enamel lamellse in their rectangular position, 
and F, the terminal or fibrous part of the enamel, in which the extent of the 
colour is marked by a vertical line. 225 linear. 
Fig. 7- A transverse section of the same tooth, showing, D, the dentine, and E, the 
enamel, in which the component fibres of two layers, the decussation and 
their continuance in the external part of the tissue, are seen. 225 linear. 
Fig. 8. An oblique longitudinal section from the base of the same tooth, in which E, 
the alternate layers of the enamel lamellse, are cut transversely and lon- 
gitudinally. In this part of the tooth the external part of the enamel is 
not fully developed. 
4 c 2 
