214 RAINEY, ON DENTAL TISSUES. 
state of a perfect tooth, the latter retaining nearly the same 
width until the process of calcification is completed. How- 
ever, I may notice, that in a cusp about one eighth of an 
inch in length, taken from a feetal calf, the membranous 
border constituted at least a tenth part. This structure, 
when all the parts of an uncut tooth are in situ, is situated 
between the enamel and dentine pulps, its surfaces bemg 
respectively in contact with the corpuscles of each and its 
free margin lodged in the groove formed by their union, to 
which groove it is united by exceedingly fine connective 
tissue. The surface of the membranous matrix is not smooth, 
but pitted, and the lateral borders appear to be undulating, 
these presenting the same irregularity of form as that pre- 
sented by the surface of dentine which is in contact with the 
rods of enamel. Before calcareous particles begin to be de- 
posited on the membranous matrix, it has no appearance of 
being divisible into layers; but afterwards its division into 
two layers can be demonstrated, one layer following the lower 
surface of the layer of enamel in progress of formation, and 
the other the corresponding surface of the incipient layer of 
dentine. Its presence in these situations after a time be- 
comes obscured by its intimate connexion with these tissues. 
In fact, one layer may be regarded as the membranous 
matrix of the dentine, and the other as the membranous 
matrix of the enamel. But this will be better understood 
when the process of calcification is considered. As respects 
the structure of this part, it seems to me to be more allied 
to cartilage than to any other description of tissue, although, 
in its anatomical characters, it differs materially from it. 
The membranous matrix appears to be made up of very 
delicate flattened corpuscles of different shapes and sizes, 
but generally longer in the vertical than in the transverse 
direction of the cusp. Near its lower part these corpuscles 
are imperfectly defined, and in all parts of it they are 
partially separated by spaces more or less distinct in different 
cusps, and in different parts of the same matrix. The matrix, 
when in situ, bemg contiguous to the dentine and enamel 
organs, has, after its removal, frequently patches of their 
corpuscles left upon it, which, from their distinctness, and the 
regularity of their form, cannot be mistaken for those of the 
matrix itself. 
Having now described this part with some degree of 
minuteness—though not, I conceive, more so than is com- 
mensurate with its physiological importance, inasmuch that 
it not only presents the earliest conditions both of dentine 
and enamel, but is also the part on which the process of 
