PROGRESS OF MICROSCOPICAL SCIENCE. 
37 
is used to designate that variety of vaso-dentine in which the matrix 
is arranged in concentric layers round the canals, like the laminae of 
an Haversian system in bone, and in which spaces like the lacunae 
of bone occur. The author would not propose to introduce any new 
terms, hut to render more precise and definite the meaning attached to 
the terms vaso-dentine and osteo-dentine, premising that the applica- 
tion of the two words will be greatly altered by so doing. The author 
defines vaso-dentine as a modification of dentine which is permeated 
by a system of canals far larger than ordinary dentinal tubes, which 
anastomose freely with one another, and contain capillary blood-vessels 
and nothing else. That is to say, each several canal contains a 
capillary of the same calibre as itself, and no cellular or other pulp- 
tissue, for which, in fact, there is no room ; the canals were formed by 
the enclosure of capillaries of the pulp in a calcified matrix. True 
dentinal tubes may co-exist with the large capillary canals ; hut if 
they do, they radiate from the central pulp-chamber and not from the 
canals : in the most typical vaso-dentine, such as that of the hake, the 
matrix is solid and there are no true dentinal tubes. Yaso-dentine is 
developed from a sharply defined “membiana eboris,” or layer of 
odontoblast cells. Osteo-dentine, on the other hand, is also per- 
meated by a system of large channels, but these do not (except as an 
accident) contain capillary blood-vessels, nor were they developed 
around capillaries. True “ dentinal tubes ” can perhaps hardly be 
said to exist ; but the tubes of small calibre which do exist radiate, 
not from a common pulp-chamber, but from the several canals. Its 
greatest distinction from vaso-dentine lies in the manner of its develop- 
ment. It is not (if we except a thin outer layer of hard dentine with 
which it is often clothed) developed from a specialized layer of odonto- 
blast cells ; but calcifying trabeculae shoot rapidly from the interior 
of the first-formed dentine cap through the whole substance of the 
formative pulp, and the canal-system ultimately formed is due to the 
partial coalescence of these ossifying trabeculae leaving interspaces 
between them. The canals have therefore nothing whatever to do 
with the blood-vessels of the pulp, and therefore do not correspond 
very closely with those of vaso-dentine. Osteo-dentine is thus not 
derived from the calcification of a “ membrana eboris,” or special 
layer of odontoblast cells, but by ossification (of cells like osteoblasts) 
shooting through its whole mass. Thus the tooth-pulp can be bodily 
withdrawn from a tooth consisting of vaso-dentine by tearing across 
the capillaries only, and the interior of the dentine cap will be left 
smooth ; but the pulp can by no possibility be withdrawn from a tooth 
which is advancing in calcification into osteo-dentine, because it is 
permeated through and through by a network of calcifying trabecula;. 
It is possible by careful observation to distinguish in sections of dried 
teeth true vaso-dentine from osteo-dentine ; the majority of teeth con- 
sisting of the latter tissue ordinarily pass as consisting of the former 
(e. g. the teeth of the pike, of many Plagiostomi, which really consist 
of osteo-dentine, but are always described as vaso-dentine). The 
teeth of the hake are selected as an illustration of vaso-dentine ; they 
have large pulps, richly vascular, and red blood circulates abundantly 
