Page 19 - My FlipBook

OF THE LOWER-JAW. 3
great many processes, that are connected with the bones of the
Face and Skull. The lower and anterior parts of the Upper-
Jaw are more uniform, making a kind of a circular sweep from
side to side, the convexity of which is turned forwards ; the
lower part terminates in a thick edge, full of sockets for the
Teeth. This edge is called in each bone the Alveolar Process.
Behind the Alveolar Processes there are two horizontal lamellae,
which uniting together, form part of the roof of the Mouth,
which is the partition between the Mouth and the Nose.
This plate, or partition, is situated about half an inch higher
than the lower edge of the Alveolar Process ; and this gives the
roof of the Mouth a considerable hollowness. (c)
The use of the Upper-Jaw is to form part of the Parietes of
the Mouth, Nose, and Orbits ; to give a basis, or supply the
Alveolar Process, for the superior row of Teeth, and to counter-
act the Lower-Jaw ; but it has no motion itself upon the bones
of the Head and Face.(d)

OF THE LOWER-JAW.
As the Lower-Jaw is extremely moveable, and its motion is
indispensably necessary in all the various operations of the

Man. Obliteration of the facial portion of the mesian premaxillary
suture commonly takes place as life advances in the Anthropoid Apes.]
(c) [The hollowness and breadth of the palate vaiy in individual
crania. It will be also found of greater comparative length in prognathic
skulls. In the larger number of Australian crania, and in those of other
dark-skinned races which approach the Australo-Tasmanian type, the
bony palate is relatively of great breadth and length.]
(d) [The fixity of the bones constituting the upper jaw is a character
common to Mammalia, and contrasts with the moveable condition of
the upper mandible in birds—the distensibility resulting from the elastic
ligamentous connection which subsists between the premaxillary and
maxillary bones in the constricting serpents—the moveable articulation
of the superior maxillary in the poisonous serpents'—and with the loose
connection of the corresponding bones in fishes, which permits, in
addition to the ordinary movements, those of protrusion and retraction.]