of the skull. The capacity of the cranial cavity undergoes no change,
but the parietes are thickened, especially at the line of the lambdoidal
suture, preparatory to the development of the great occipital ridge,
which diverges from the end of the sagittal crest. The zygomatic
arches are strengthened and expanded, the superior maxillaries
produced, while the intermaxillaries having given passage to the
crowns of the large permanent incisors, appear to have fallen in.
In the Orang the intermaxillary bones at this period have become
anchylosed to the maxillaries : in the Chimpanzee that confluence
is completed before the deciduous teeth are in place.
The microscopic structure of the teeth of the Quadrumana
is conformable throughout the platyrhine and catarhine groups,
and closely resembles that which Purkinje, Retzius, Miiller, and
myself have described in the Human subject. As this structure
will be more particularly elucidated in the chapter on the Human
teeth I shall here merely mention' the most obvious differences
which the teeth of the Quadrumana present, and which are manifested
not only in the Baboons and Monkeys but in the most
anthropoid Ape, viz : the Chimpanzee(l). In the incisor and canine
the general direction of the calcigerous tubes agrees with that figured
in Fraenkel’s Thesis, fig. 1, B, and by Retzius in his “ Mikros-
kopiska undersökningar” PI. i (iv), fig. 1, in the corresponding Human
teeth. The tubes(2) in the Chimpanzee describe the same primary
curvatures, but less strongly; and the secondary gyrations are
longer and more feebly marked : they are j^ th of an inch in diameter,
and the interspace between two tubes on the same plane
equals the width of two tubes, when viewed in transverse section
near the pulp-cavity, as in PI. 119a, fig. 2 ; nearer the enamel the
interspaces are wider ; hut in general they are more closely arranged
and relatively more numerous, besides being straighter than in the
Human subject. They maintain the same diameter through three-
fourths of their course ; divide sparingly, except close to the enamel
boundary and the periphery of the fang: in this part of the tooth
the minute lateral branches are most numerous. The calcigerous cells
of the dentine(3') are most conspicuous, as usual, near the periphery
of the crown, where their well-defined semi-circular contour is seen
(1) PI. 119 a, fig. 1 & 2. (2) lb. fig. 1, t, t. (3) lb. fig. 1, d-, d\
with its convexity next the enamel: from ten to twelve dentinal tubes on
the same plane are included in the diameter of a peripheral calcigerous
cell: the cells decrease in size and increase in number, and
become less definable as they become situated nearer the pulp-cavity.
The enamel fibres(l) are more wavy, even, than in the human teeth :
they are ^ th of an inch in thickness, and manifest the striated
indication of their cellular origin as distinctly as in the human
teeth. The vertical fibres ascending from the summit of the crown
of the canine of the Chimpanzee described twenty acute-angled
undulations in their course. In the section examined, the bend
in one direction transmitted more light than in the opposite, and
gave an appearance of waves upon the cut surface of the enamel.
This is the character attempted to he shown by Fraenkel in fig. 4,
of his Thesis, and which Retzius says he had not succeeded in
observing in human enamel. The lines of growth or strata of the
enamel were best displayed in transverse sections of the incisors and
canines. The cement is thickest at the apex of the fang; the Pur-
kingian cells are traceable to near the neck of the tooth, over which
the clear basis of the cement is continued upon the enamel : the tuhuli
continued from the cells are most numerous on the side next the
dentine : they form likewise rich anastomotic plexuses in the interspaces
of the cells, besides communicating with peripheral ramifications
of the tuhuli of the dentine: their diameter is grcsth
of an inch.
C H A P T E R X.
T E E T H OF B I M A N A .
173. H a v in g reached in the Chimpanzee the highest step in
the series of the brute creation, our succeeding survey of the Human
dental system, expanded by retrospective comparisons, becomes
fraught with peculiar interest, since every difference so detected
establishes the true and essential characteristics of that part of
Man’s frame.
(1) PI. 119 a>, fig. 1 e, e.
G G 2