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26 DIGASTRICUS.
of elevation ; so that these Muscles act, both when the Lower-
Jaw is raised, and when it is depressed
: yet they do not assist
either in raising or depressing it. (b)
DIGASTRICUS..
It is situated immediately under, and a little upon the in-
side of the Lower-Jaw, and outside of the Fauces, extending
from the Mastoid Process to the Chin, nearly along the angle
made by the Neck and Chin, or Face. The name of this Muscle

(b) [The pterygoids vary in size and function in the different families
of Mammalia. They are usually largely developed in herbivorous and
frugivorous animals, where they are in direct relation to the lateral and
antero-posterior motions of the jaw in mastication. In the Chimpanzees
and Orangs, the force and size of the internal pterygoid is evidenced by
the roughness and elevations which exist on the internal surface of the
posterior border of the ascending ramus and angle of the jaw. (1) In the
Rodents, the internal pterygoid, like the masseter, is employed in draw-
ing forward as well as in raising the mandible. To increase the obliquity
of its fibres and the backward extent of surface for their insertion, the
angle of the jaw is prolonged posteriorly. The Ruminants, and grass-
feeding animals generally, have these muscles of large size. In the
typical Carnivora, on the other hand, the principal pterygoid is simply
an elevator of the jaw, not a rotator or protrusor. In the Cat, the
larger muscle (external Pterygoid, Straus-Durckheim ; internal Pterygoid,
Cuvier) is flat and of considerable size
; it has its origin from the whole
length of the lateral border of the guttural part of the palatine
bone, and from its corresponding orbital surface, and passes outwards,
backwards, and downwards, to be inserted into the inner surface
of the lower border of the jaw, into the tendinous raphe common
to it and the masseter, and into the inner surface of the coronoid.
The smaller slip (internal Pterygoid, Straus-Durckheim) is almost
blended with the preceding it is placed behind, and is in part internal
;
to and under the principal muscle. None of the fibres of the pterygoid
in the Cat are attached to the condyle or to the interarticular cartilage.
These muscles, as do the temporal and masseter, present an admirable
instance of adaptation to the type of dentition, and to the structure of
the joint. (2)
(1) Vide Owen, Zool. Trans., vol. iv.
(2) Vide Straus-Durckheim, op. et loc. cit. ; Cuvier, op. cit., p.