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DIGASTRICUS. 27
expresses its general shape, as it has two fleshy bellies, and of
course a middle tendon, (d) Yet some of its anterior belly does
not arise from the tendon of the posterior, but from the Fascia,
which binds it to the Os Hyoides. These two fleshy bellies do
not run in the same line, but form an angle, just where the
tendon runs into the anterior belly ; so that this tendon seems
rather to belong to the posterior, which is the thickest and
longest.
This Muscle arises from the Sulcus made by the inside of the
Mastoid Process, and a ridge upon the Temporal Bone, where it

(eQ [The name " digastricus " is not equally applicable to this muscle
in all the Mammalia in which it is found. In the Apes, as in Man, it
consists of two bellies, united by a middle tendon, which passes through
the stylo-hyoid. But the digastric of the higher Quadrumana differs
from the same muscle in Man in the greater size and strength of the
anterior belly. Duvernoy describes this portion of the muscle in the
Gorilla as being large and flat In the Chimpanzee, the anterior
fasciculus, according to Vrolik, is relatively stronger than in Man, and
is less separated from its fellow of the opposite side. Thereby, he
observes, a tendency is shown to the condition which exists in the other
Apes, " in which the anterior fasciculi of the digastric are so developed
as to fill up all the interspace between the two rami of the lower jaw."
This expansion of the anterior portion of the muscle he has observed
in the Orang and Gibbon, but it is most remarkable in the Macaques
and Cynocephali. In the latter, the term " digastric " might be applied
to the posterior bellies of opposite sides, for their tendons unite in
front of the os hyoides to form an arch, from the convexity of which the
two anterior ventres, which are in close proximity the one to the other,
take their origin by an aponeurotic expansion. By this arrangement
the power of the muscle, as a depressor of the jaw, must be considerably
augmented, and it would appear to be a provision in direct relation
with the more carnivorous and ferocious habits of the Baboons and
Mandrills. Professor Vrolik states that in the Loris (Stenops) the
structure of the digastricus points to a transition from the Quadru-
manous type to the simple form which it takes in the Carnivora,
there being only an indication of the intermediate tendon. In the
Rodents (with the exception of the Rabbit), and in the Ruminants
generally, it is biventral. On the contrary, in the Carnivora, the
Kangaroo, the Sloths, the Elephant, the Hog, the Hyrax, it is only a
single-bellied muscle. Straus-Durckheim, however, describes it in the
Cat as being interrupted a little behind the angle of the jaw by a
tendinous intersection, which gives rise to new fleshy fibres ; and
Vrolik has also noticed the occurrence of aponeurotic fibres in the