INTERNAL ANATOMY. 321 
multiplied. In Plate 9, fig. 8, the spine has reached nearly its full size, but is 
imbedded so deep in the common cuticula that its apex is some distance below 
the free surface. In fact but very few spines retain their connection with the 
basal matrix-cell when the wearing away of the general surface exposes their 
tips. When each spine reaches a length of approximately 0.5 mm. the further 
_ deposition of basal layers by the matrix-cell ceases, and the spine becomes 
separated from it and is simply imbedded in the surrounding cuticle. The 
continual formation of the cuticle below and its erosion above brings the tip 
of the spine to the surface and successively the remaining portions (Plate 9, 
fig. 7), the spines being evidently harder and more resistant than the cuticle 
surrounding them. The base of the spine is carried farther and farther away 
from the epithelium by the continued formation of new layers of the general 
cuticle, while its upper portion is progressively more and more exposed above, 
finally becoming entirely free, and falling away. The basal cell appears to 
.enter upon the formation of a new spine in a short time, as frequent instances 
are found in which a very young spine is in process of development immediately 
beneath the base of a mature one, which has evidently been produced by the 
same matrix-cell. 
This relation of the palatal spines to the epithelium and to the common 
cuticle is shown in Plate 9, fig. 7, under low magnification. The free ends of 
the spines here are relatively few in number in the thin section, while others 
are seen at various levels. This appearance is not due to any obliquity of the 
section, as might be readily supposed. The plane of the section is nearly trans- 
verse to the long axis of the fold, ¢ is its free margin, a its dorsal surface, and b 
its ventral one. At e¢ there is found the typical thickness of the cuticle of the 
general lining of the buccal cavity. It increases very rapidly on the ventral 
surface of the palatal fold, but abruptly thins away to a very thin layer at the 
free margin. In this region a deep gland-like infolding of the epithelium occurs 
in all the sections, characterized by the presence of a very great number of large 
unicellular gland-cells extending down below the basement-membrane. Simi- 
lar cells are found continuing around the free margin and over the dorsal surface 
of the fold. One of these gland-cells is shown in Plate 8, fig. 2. Here the epi- 
thelium had been stripped away accidentally, so that the apex a, showing the 
secretion discharge from the cell, appears at the level of the basement-membrane 
d. The nucleus of the cell is not contained in this section, but is relatively 
poor in chromatin. The cytoplasm in the lower proximal portion of the cell 
shows a fine reticulum with deeply staining nodal granules. These gradually 
