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22 PTERYGOID^US internus and externus.
PTERYGOID^US INTERNUS.
It is situated upon the inside of the Lower-Jaw, opposite to
the Masseter, which is upon the outside. It is a strong short
Muscle, a little flattened, especially at its insertion. It arises
tendinous and fleshy from the whole internal surface of the
external Ala of the Sphenoid Bone ; from the external surface
of the internal Ala, near its bottom ; from that process of the
Os Palati that makes part of the Fossa Pterygoids ; likewise
from the anterior rounded surface of that process, where it is
connected to the Os Maxillare superius. From thence the
Muscle passes downwards, a little outwards and backwards, and
is inserted tendinous and fleshy into the inside of the Lower-
Jaw, from the angle, up almost to the groove for the admission
of the Maxillary Nerve, where the surface of the bone is
remarkably scabrous.
The Use of this Muscle is to raise the Lower Jaw ; and from
its direction, one would suspect that it would bring the Condyle
a little forwards ; but this motion is contrary to that of the
Lower-Jaw, for it is naturally brought back when raised.

PTERYGOIDJEUS EXTERNUS,
Is situated immediately between the external surface of the
external Ala of the Pterygoid Process, and the Condyle of the

in which this muscle attains considerable size, it is common to find the
depth of the fossa from which it arises increased by the production of
its boundaries in the form of osseous ridges or crista, which spring from
the surfaces of the frontal, the parietal, and the occipital bones. The
direct relation which exists between the development of the temporal
and the condition of the dental apparatus is well illustrated by a
comparison of the male and female and immature and adult crania of
the large Anthropoid Quadrumana. Amongst these the maximum of
extension and depth of the temporal fossa is to be seen in the skull of
the adult male Gorilla, where a lofty sagittal crest is produced by the
union of the frontal ridges at the coronal suture, and behind is con-
tinued into two thick salient occipital crista?. The same thing is re-
peated, although in a somewhat inferior degree, in some skulls of the