ENAMEL OF THE TEETH. 99 
however, much less striking in human teeth, so that the ques- 
tion as to which of the two views is correct must remain un- 
decided. 
What, then, is the process of formation of these enamel- 
prisms? According to Purkinje and Raschkow, the crown of the 
growing tooth is surrounded externally by a peculiar membrane, 
the enamel-membrane, the inner surface of which is composed 
of short hexagonal fibres, which stand perpendicularly upon the 
membrane, and are directed towards the enamel, so that each 
fibre of the enamel-membrane corresponds to an enamel-fibre. 
On examining a portion of this membrane, particularly that 
part which les nearest to the root of the tooth, we readily 
recognize in it the characteristic nuclei, some of them being 
furnished with nucleoli. They le in a minutely granulous 
substance. This granulous aspect, however, is seen to be pro- 
duced, in many situations, by granulated cells which contain the 
nuclei. Hach nucleus is surrounded by a circular areola of 
small granules, and seems to lhe in a minutely granulated 
globule, which we know to be the rudimentary form of 
most elementary cells. Some of these cells are prolonged 
into very delicate fibres; they appear to be young cells of 
areolar tissue; most of them, however, are round. The 
fibres or prisms of the membrane, which have a direction 
from its inner surface towards the enamel-fibres, have 
assumed an hexagonal form, which Raschkow attributes to 
their close contact. They very closely resemble the columnar 
epithelium upon mucous membranes, only that they are 
prismatic in their entire length, that is, so far as they project 
out from the membrane to which they are attached. I am 
inclined therefore, to regard them as merely elongated cells. 
In the recent state they also contain a very distinct nucleus, 
which encloses its nucleolus. (See pl. III, fig. 4.) In the upper 
part of the enamel-membrane they lie quite close together ; 
but in the portion nearest to the root of the tooth, they 
diminish in number and stand insulated, so that at this 
part the structure of the membrane beneath them may 
also be recognized, and I suppose the round cells before 
mentioned to be the earlier condition of these prismatic 
cells. What, then, is the relation which these prismatic cells 
of the enamel-membrane bear to the prisms of the enamel? 
