690 
CONTRIBUTIONS TO ZOOLOGICAL ANATOMY. 
submaxillary fascia and gland being removed, the greater number 
of them are at once completely exposed. 
The Digastricus is, as its name implies, a double-bellied muscle, 
fleshy at either extremity, and tendinous in the centre. It is the 
most superficial of the muscles contained within the branches of the 
lower jaw, and is placed immediately within its lower edge. It 
arises posteriorly from the styloid process of the occipital bone, 
along with the occipito-maxillaris and the occipito-styloideus, and 
from thence extending downwards and forwards, under cover of 
the angle of the lower jaw, and inclining inwards to the side of the 
body of the os hyoides, becomes tendinous to enter the canal in the 
tendon of the stylo-hyoideus, by means of which it is indirectly at- 
tached to the os hyoides. Leaving this canal, it again becomes mus- 
cular, and, extending forwards and inwards, becomes inserted by 
a broad and tendinous expansion into the inferior edge of the lower 
jaw, behind the symphysis. The posterior belly is related externally 
to the ramus of the lower jaw and the pterygoideus internus, and 
internally to the stylo-hyoideus, the constrictor pharyngis anterior 
and medius. The anterior belly is placed immediately beneath the 
skin, from which, however, it is in part separated b}^ the submax- 
illary artery : above, it is covered by the mylo-hyoideus, and 
along the internal side is the submaxillary gland. In its action 
this muscle will carry upwards and forwards the os hyoides, and 
by this the base of the tongue will be elevated within the mouth : 
but if the os hyoides be drawn down and fixed, the muscle will 
then depress the lower jaw, by the posterior belly taking its point 
of fixion at the occipital bone, and the pivot of motion at the tem- 
poro-maxillary articulation. 
The Stylo-hyoideus is situated along the upper edge of the pos- 
terior belly of the digastricus. It is rounded in form, and arises 
posteriorly and superiorly by a strong muscular tendinous origin 
from the lower edge of the base of the styloid appendage of the 
temporal bone (the great cornu of the os hyoides of veterinary 
anatomists generally), and, extending along the posterior belly of 
the digastricus, it becomes inserted , by a flattened tendon, along 
the side of the body and the posterior cornu of the os hyoides. 
The inner surface of this tendon is perforated by a canal, which is 
lined by a synovial sheath, and through which the tendon of the 
digastric plays, as through a pulley. The relations of this muscle 
are similar to those of the posterior belly of the digastricus, and 
the combined actions of the two stylo-hyoids is analogous to that of 
the former muscle, on the os hyoides. If one of them acts alone, 
then the os hyoides and the larynx generally will be draw'n to the 
corresponding side. 
The Mylo-hyoideus is situated immediately under cover of the 
