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356 DENTAL ANAT03IY.

scope. This necessarily requires a considerable amount of experience
and skill in the manipulation and preparation of material, so that to
the unpractised observer a proper determination of the things which one
may see is not always an easy matter. On this account I have chosen
to follow the conclusions of the recognized authorities, especially the
excellent treatise on dental anatomy by Charles S. Tomes, in this brief
statement of the histology, rather than trust the accuracy of my own
observations on the same. Since the histology of human teeth has been
more fully made out than perhaps the histology of those of any other
animal, it is here taken for illustration, although I am fully aware that
important deviations from the structure here described are to be met
with among the Vertebrata.
Dentine.—As we have already seen, the tooth consists of a dentine
body with a central cavity lodging the pulp, an enamel-capped crown,
and cementum-covered roots. The dentine is a hard, highly elastic,
translucent substance of a yellowish-white tinge, having a silky lustre
upon fracture. It is composed of an organic matrix highly impreg-
nated with calcareous salts ; through this matrix closely-set parallel
tubuli radiate from the pulp-cavity toward the periphery in a direction
at right angles to the suriiice of the tooth.
Of perfectly dry dentine the following chemical analysis is given by
Von Bibra :
Organic matter (tooth-cartilage) 27.61
Fat 0.40
Calcium phosjiliate and fluoride 66.72
Calcium carbonate 3.36
Magnesium phosphate 1.18
Other salts 83
The organic basis of the matrix, although closely related to that of
bone, is said not to be identical with it, and is hence called " dentine" or
" tooth-cartilage ;" it is perfectly structureless and transparent. After the
tooth has been decalcified by submitting it to the action of dilute acid
for a few days, the matrix will still preserve the characteristic shape of
the tooth, and can readily bo studied.
As already stated, the tubuli, which are likewise known as dental
tubeii, permeate the matrix in all directions, opening freely upon the
walls of the pulp-cavity, by which arrangement all i)arts of the dentine
are brought into direct connnunication with the central nutrient organ,
the pulp. They are most nearly approximated and their diameters
greatest at their commencement on the walls of the pulp-cavity, but,
pursuing a somewhat wavy course, gradually diminish in size, owing
to the numerous branches Avhich they give off. These branches, although
not uniform in size, anastomose freely with those of the neighboring
tubuli, and frequently show varicosities in their course. They termi-
nate either by gradually fading out, by anastomosing with other
branches, by ending in loops, or by entering the enamel and cement-
um layers.
AVhile the dental tubes may be said to be channelled out in the sub-
stance of the dentine cartilage, the walls of the tubidi are not formed
by this cartilage, but each tubuli is furnished with a structure knoA^n as