Page 18 - My FlipBook

Z OF THE UPPER-JAW.

remain distinct through life, (b) They are very irregular at their
posterior and upper parts, sending upwards and backwards a

distinct until the period of old age. In Man, on the contrary, the pro-
cess of anchylosis (with the exception of a portion of the suture
on the palate, which usually remains until after birth) is com-
pleted before the termination of intra-uterine existence. It is, there-
fore, only in the fcetal condition that Man can be said to possess
an intermaxillary bone ; and even this has been denied by many
writers, on the ground that the fissure of separation cannot be
traced through the external alveolar plate. On the other hand,
analogy, the constant existence of the nasal and palatal portions of the
maxillo-interrnaxillary fissure in intra-uterine life, and the entire
separation of the incisive portion of the superior maxillary bone in
certain cases of deformity (double hare-lip), are strong arguments for
admitting the premaxillary as an original element of the human skull.
Direct observation appears, however, to have definitively settled the
question. Some years since Dr. Leidy announced to the Academy of
Natural Sciences of Philadelphia (1) that he had found the inter-
maxillary entirely separable in an embryo of one inch eleven lines in
length. The division in this case was traceable through the alveolar
ridge at a point corresponding to the separation between the incisor and
canine alveoli. Figures of the preparation tf ken from those published
in the Proceedings of the Academy will be found amongst the Engravings
which illustrate this work. The more recent researches (2) of Robin
and Magitot strongly confirm Dr. Leidy's observation, these observers
have discovered the existence of a separate formative cartilage for each
premaxillary, in which an osseous point is developed two or three days
after the first deposition of ossific matter in the alveolar edge of the
formative cartilage of the superior maxillary.
It is stated by Scemmerring, that vestiges of the maxillo-inter-
maxillary suture are to be noticed in Negro crania. Dr. Prichard long
since denied any constancy of difference between the melanous and
leucous varieties in this respect, and extended observation will verify
bis statement. In skulls of all nations, it is not very uncommon to rind
Si .me small vestige of the suture both on the palate and in the floor of the
nares, extending outwards from the anterior palatine canal ; more rarely
it may be traced on the palate to within a short distance of the
alveolus. An instance of the permanency of any portion of the suture
on the face has never fallen under the Editor's notice.]
(b) [Anchylosis between the superior maxillary bones is exceptional in
(1) Proceed. .Acad. Nat. Sciences, Philadelphia, Jan., 1849, p. 145.
(2) Vide Journal de la Physiologic Edited by Dr. Brown-Sequard.
Janvier, 1860, p. G.