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4 OF THE LOWER-JAW.
Teeth, it requires to be more particularly described. It is much
more simple in its form than the Upper, having fewer processes,
and these not so irregular. Its anterior circular part is placed
directly under that of the Upper-Jaw; but its other parts extend
farther backwards.
This Jaw is at first composed of two distinct bones (e) but
;
these, soon after birth, unite into one, at the middle of the chin. (/)
This union is called the Symphysis of the Jaw. Upon the
upper edge of the body of the bone is placed the Alveolar Pro-
cess, a good deal similar to that of the Upper-Jaw. The
Alveolar Process extends all round the upper part of the bone,

( which forms a lateral half, is one of the few osteological characters
which Professor Owen enumerates as being common and peculiar to the
Mammalia. (1) In the human subject, authorities are at variance as to
the ossification of the inferior maxilla. Kerckringius describes a
separate ossific centre for the coronoid process ; and he is confirmed by
Autenrieth, Spix, and Beclard. Autenrieth enumerates two other separate
points of ossification—one in the condyle, the other in the angle. Another,
forming the inner border of the alveolus, is described and figured by
Spix, who also admits those mentioned by Autenrieth. Cruveilhier
allows the separate ossification of the internal alveolar plate, but denies
the existence of other secondary nuclei. On the other hand, J. F.
Meckel and Nesbitt maintain the ossification of each lateral half from a
single centre. The former anatomist attributes the appearance of the
separation of the internal alveolar plate to the depth of the groove or
fissure for the mylo-hyoid nerve. One reason for the discrepancy which
prevails with regard to the ossification of the mandible, is the rapidity
with which the process is carried on, and the early period at which it
commences. Bony deposit is found in the inferior maxillary earlier
than in any other bone except the clavicle. (2)]
(/) [Union of the lateral halves takes place during the first year after
birth, but a trace of separation may be found at the upper part in the
beginning of the second year. (3)]

(1) On the Classification and Geographical Distribution of the Mammalia,
p. 13.
(2) Quain's Anat., 6th edition, vol. i., p. 78.
(3) Op. cit., p. 78.