GEOWTH OF THE TOOTH OF ECHIHITS. 
403 
function of these developments, that I have named them “ Soldering particles.” These 
bodies were first described by Professor Williamson as the instruments by which the 
separate elements of the forming tooth are united into a coherent mass, the vacuities 
between them constituting the cavities and tubes of the matured tissue. Though the 
interstitial nature of the tubes, lacunse, and canaliculi was pointed out by Quekett, and 
in this much Professor Williamson was anticipated by him, still the method by which 
this character of the tissue is produced had never been before described. 
Professor AVilllmuson was, however, quite wrong in some important points, both in 
the anatomy and anatomical relationship of the soldering particles. He asserts that 
they &refree, that they are unconnected with each other, and that they never become 
anchylosed to one another : in all three particulars he is mistaken. 
The soldering particles are always attached firmly, and in fact united to the elements 
of the tooth on w’hich they are seen, and cannot be removed without violence. Indeed 
it is by this absolute adhesion that the structures of the tooth are soldered together 
and cease to be separable. The mere development of these granules among the other 
elements of the tooth, if still free, would only add to the complication of the structures 
without contributing to their cohesion. The nature of these particles can be best 
investigated by examining the plates when studded with them and in a state of con- 
siderable advancement of growth, as is represented in Plate VIII. fig. 1. Portions of 
the plates may be broken up about midway between the two extremities of the tooth 
with the points of needles, the soldering particles remaining firmly attached to their 
surface : the particles can occasionally be swept otf the plates by force ; but it usually 
happens that, when once formed, they hold together as one, and that, however the plate 
breaks, its fractured edge corresponds with the distribution of the soldering particles. 
The specimen figured at Plate VIII. fig. 1 consists of portions of four plates held 
together by the soldering particles : the relation of the particles to one another is here 
seen, and the characteristic appearance which they present when viewed in face. By 
a happy fracture of the most superficial plate, it exposes to view the reticulations of the 
flabellifoim processes, passing out between that plate and the next; and on them is 
also seen a profusion of soldering particles w^hose function it is to unite them with the 
contiguous plates. 
But the soldering particles are not only adherent to the surface on which they are 
formed ; they have a special connexion infer se. It occasionally happens that a whole 
sheet of the particles will become detached from the surface of a plate more or less 
completely, and yet retain their relative position as respects each other (see Plate VIII. 
figs. 3, 4, & 5, b, d). That this mutual attachment of the contiguous soldering particles 
is over and above their adhesion to the plate on which they rest, may be most con- 
clusively demonstrated in such a specimen as is represented at fig. 3 of Plate VIII., in 
which a number of the soldering particles remain upon and adherent to the surface of a 
portion of broken plate, while others of the same set extend beyond its margin — the 
latter retaining their relative position inter se just as undisturbedly as the former. 
MDCCCLXI. 3 K 
