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OF THE BONY PART OF A TOOTH. 47
and the whole of the root of a Tooth. It is a mixture of two

portion to the primary curves of the dentinal tubes at any particular
spot, and cross them at right angles." (1) These lines vary in human
teeth in intensity and in number. In the teeth of some animals they
present a beautiful appearance ; especially is this the casein some of the
Cetacea and Pachydermia, and in the Walrus. A tendency to break into
laniellso is not unfrecpiently found in these and in f< issil teeth, and is some-
times indicated in fresh human teeth and in tooth cartilage. In the
human tooth, the extremities of the better defined contour lines terminate
in irregularly-shaped cavities interglobular spaces, Czermak), situated at,
the surface of the dentine, immediately within the cement and enamel.
Mr Salter describes these spaces or cavities as being more or less club-
shaped, with the butt end of the club towards the surface, and the
pointed or attenuated end stretching obliquely inwards and upwards
towards the pulp cavity. They vary in size ; their walls are formed by
spherical masses or globules of dentine, which project into the cavity ;
and they are traversed by the dentinal canals, the number of which
will vary with the size of the cavity. The dental canals permeate the
dentine globules, five or six traversing a large globule : in the dried
specimen, when the cavity contains air, the individual tubules may be
traced from one globule to another, skipping, so to speak, the inter- lo-
bular space. Kolliker asserts that, during life, the spaces are filled with
a soft substance resembling tooth cartilage, which is permeated by the
tubules. He says that this soft substance " offers more resistance to
hydrochloric acid than the matrix of the true ossified tooth, and on this
account can be isolated exactly like the dentinal tubes." (2) In the
smaller spaces, the spherical character of the tissue composing the
walls is not so apparent ; the cavity has a more jagged outline,
and resembles in appearance a lacuna of bone, the more so as it
is traversed by the dentinal canals. In the fang, these smaller
interglobular spaces and globules constitute what has been termed
the 'granular layer' by Tomes. (3) True lacunae have been rarely
seen by Kolliker in dentine, and never at a distance from the cement
boundary. Interglobular spaces and globules sometimes occur in the
interior of the dentine of the fangs ; and on the surface of the pulp
cavity, the projecting spheres of dentine may produce irregularities or
stalactite-like formations, visible to the naked eye. In many teeth,
the interglobular spaces are absent, or but little marked: they are
al ways most conspicuous in those specimens in which the enamel exhibits
irregular development, and there appears to be a relation between the
contour markings in the dentine and the grooves and irregularities in

(1) Op. cit., p. 255.
(2) Kolliker, op. cit., p. 294.
(3) Tomes, Lectures on Dental Physiology and Surgery, p. 48.