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OP THE MOTION IN THE JOINT OF THE LOWER-JAW; 13
OF THE MOTION IN THE JOINT OF THE LOWEll-JAW.
The Lower-Jaw, from the manner of its articulation, is sus-
ceptible of a great many motions, (w) The whole Jaw may be
brought horizontally forwards, by the Condyles sliding from the
cavity towards the eminences on each side. This motion is per-
formed chiefly when the Teeth of the Lower-Jaw are brought
directly under those of the Upper, in order to bite, or hold any
thing very fast between them.

packet of convoluted vessels, sends off from each tubular sheath second-
ary processes of various shapes, into which no blood-vessels enter."
Mr Kainey's account of the structure of these processes has since been
confirmed in most particulars by Kolliker. (1)]
(w) [The form of the osseous surfaces entering into the temporo-
maxillary articulation, and the diversities of motion which it admits,
are so modified to suit the functions and necessities of the differ-
ent families of Mammalia, that there is no portion of the skeleton
calculated to yield more certain information to the naturalist. In
the frugivorous Quadrumana the articulation is loose, as in Man, and
permits within certain limits each kind of movement—viz., in the
vertical, the anteroposterior, and lateral directions. The principal
differences between bimanous and quadrumanous structure in this
joint are the somewhat greater flatness of the glenoid surface, the minor
development of the anterior articular eminence, and the constancy and
size of the post-glenoid ridge in the latter. In the Carnivora the con-
dyle of the lower, jaw is an oblong cylindroid process of considerable
length, placed transversely, almost, if not quite, in a straight line with
its fellow of the opposite side. The receiving surface is bounded
anteriorly and posteriorly by salient ridges, which increase its depth,
and limit the chief motion of the jaw to the vertical direction, per-
mitting only in addition a slight lateral gliding of the condyles. The
development of the anterior ridge varies in different species. In the badger
both processes project in such a manner as almost to embrace the con-
dyle, so that in the skeleton the inferior maxilla is retained in situ
without any artificial fastening. In the placental Rodents (the Hares
excepted), on the other hand, the glenoid cavity is a deep groove ex-
cavated longitudinally under the base of the zygoma, and corresponds
with the long diameter of the usually oval condyle, which is set antero-
posteriorly instead of from side to side. In accordance with this con-
formation, the conspicuous movement of the lower jaw in the Rodents
is in the anteroposterior direction. The "nibbling" motion allowed is in

Vidt Quams Anat, sixth edit., vol. i., p. ccxhx.
(1)