388 THE HORSE. 
temporal bones. Insertion—to the coronoid process of the lower jaw. 
Action—to raise the lower jaw, and thus to assist In mastication. 
Masseter forms the prominence of the cheek. Origin—from the 
inferior surface of the zygomatic ridge. JInsertion—to the whole of the 
external surface of the angle of the lower jaw. Action—to elevate the 
lower jaw, and thus assist in mastication. 
Sryno MAXILLARIS lies behind the lower jaw. Ovigin—from the 
styloid process of the occipital bone. Insertion—to the angle of the lower 
jaw. Action—to retract the jaw and assist in opening the mouth. 
PTERYGOIDEUS EXTERNUS lies within the jaw. Ovigin—from the ala of 
the sphenoid bone. Jnsertion—into the rough depression at the inner 
side of the root of the condyle of the jaw. Action—to raise the jaw and 
draw it forwards. 
PreRYGOIDEUS INTERNUS is situated below the external pterygoid, and 
passes in a more horizontal direction. Origin—from the ala of the sphe- 
noid bone, from the palate bone, and the tuberosity of the superior maxil- 
lary bone. Znsertion—to the inner side of the angle of the jaw. Action 
—each muscle acting separately draws the jaw towards the opposite side, 
and the two acting alternately produce the grinding motion necessary fox 
reducing the food. 
MUSCLES OF THE EXTERNAL EAR. 
Six pairs of muscles move the cartilage of the ears in all directions ; 
but they are not of sufficient importance to require any description here. 
EXTERNAL MUSCLES OF THE EYELIDS. 
ORBICULARIS PALPEBRARUM is a layer of thin muscular fibre, shown at 
Fig. 1 aa. It forms a plane around the edge of the lids, extending 
upwards and downwards, and having a tendon at the inner angle, by 
which it is attached to the frontal and lachrymal bones. Its action is to 
close the lids and draw them towards the inner angle. 
LEVATOR PALPEBRH® SUPERIORIS.—Fig. 1 h is a thin slip of muscle 
which is attached above to the aponeurotic expansion and skin of the 
forehead, and below to the orbicularis palpebrarum. Its actvon is to raise 
the upper eyelid and wrinkle the brow. 
OCULAR REGION. 
Eicat muscues are lodged within the orbit for moving the eyelid and 
eye. They are severally named from the offices which they perform. , 
MUSCLES OF THE TONGUE. 
TEN MUSCLES are attached to the os hyoides, or bone of the tongue, for 
he purpose of moving it backwards and laterally, and also to serve as 
agents in the various movements of the tongue. 
MUSCLES OF THE PHARYNX. 
As THE MOUTH conTRACTS to form the funnel-shaped tube which ends in 
the esophagus, the latter is clothed with several muscles, which aid in 
driving the food backwards. ‘These are the hyo-pharyngeus and palato- 
pharyngeus and the three constrictors of the pharnyx. 
