392 
ME. S. J. A. SALTEE ON THE STEUCTUEE AND 
dependent on them and attached to them, are all the supplemental elements which enter 
into the construction of the tooth. These are four in number, namely, certain Secondary 
Plates, Cylindrical Filres, Flahelliform Processes, and Enamel Mods. 
The Secondary jylates are lappets of the same thin calcareous sheet as constitutes the 
primary plates from whose outer edge they fold inwards towards the enteric region. 
The form of the primary and secondary plates relatively, and their section, may be 
seen in the Woodcut diagram II., while the position of these tooth-elements in a 
transverse section of the tooth itself is diagrammatically represented in Woodcut I. a, h. 
The Cylindrical fibres are cylindrical only in their early form: they are certain rods of 
carbonate of lime, which, stretching inwards and downwards from the upper angle and 
outer edge of the primary plates, constitute the keel of the tooth (Woodcut I. c, <?'). 
The Flabelliform processes are reticulated growths with fan-shaped extremities, of the 
same nature as the cylindrical fibres : they pass outwards and laterally beticeen the plates 
from whose upper edge they take their origin. In their course they contribute con- 
siderably to the bulk and solidity of the body of the tooth, and, reaching beyond the 
edges of the plates, they terminate in the coarse reticulated structure which skirts the 
enteric border of the body of the tooth (Plate VI. fig. 4, b, b; and Woodcut I. d).^ 
The Enamel rods are short stout cylinders of carbonate of lime, which grow back- 
wards from the lower edge of the dorsal surface of the primary plates. They form, by 
fusing together, the white enamel which clothes, in a thin layer, the posterior aspect of 
the tooth. The structure, when completely formed, has small interstitial tubes, and is 
almost strictly horizontal, that is, at right angles to the long axis of the tooth. 
All these supplemental parts are attached to the primary plates at their point of 
origin, but are elsewhere free : thus the secondary plates are attached to the outer edge 
of the primary plates (Plate VII. fig. 2; also Woodcut II. a). The cylindrical fibres 
are attached to the upper angle and outer edge of the plates (Plate VII. fig. 3); the 
flabelliform processes to the same region (Plate VII. fig. 1), and the enamel rods to the 
posterior surface of the lower margin of the plates (Plate VII. fig. 4). When all these 
parts are formed, they are free except at the points just indicated, and each set of 
elements is placed over its successor in a loose imbrication. 
The next change consists in the development, all over the plates and fibres, of count- 
less multitudes of minute excrescences of carbonate of lime, which, by their vertical 
growth, solder together the contiguous elements of the tooth, and by their lateral 
increase of size so diminish the intervals between them as to produce a compact though 
canaliculated structure. 
The development of the tooth divides itself not unnaturally into three stages,— 
that of the primary plates, the supplemental elements, and. Anally, the general conso- 
lidation. 
Let it be recollected then that the plates (primary and secondary) constitute the mam 
portion of the body of the tooth, the bulk being increased by the reticulation of the 
flabelliform processes between the plates ; that the cylindrical fibres constitute the keel. 
