The muscles of the face comprise a number of longer or shorter strips, most of which are attached by one extremity to the bones above, and by the other to parts about the lips and nostrils below. Those attached to the former are for the most part muscles of prehension, and serve to gather up the food and retain it in the mouth during mastication. With one or two exceptions the muscles of the face are arranged in pairs, one being on one side and the other on the other.

Muscles of Horse's Head.

Fig. 371. - Muscles of Horse's Head.

A, Temporalis muscle. B, Levator palpebrae. c, Orbicularis palpebrarum. D, Supernaso-labialis or Levator labii superioris alaeque nasi. E, Supermaxilo-labialis or Levator labii superioris proprius. F, Supermaxilo-nasalis or Dilator naris lateralis. G, Orbicularis oris. H, Mento-labialis. I, Maxilo-labialis or Depressor labii inferioris. J, Zygomaticus. K, Buccinator. L, Parotid duct. M, Masseter muscle. N, Parotid gland. 0, Jugular vein. P, Mastoido-humeralis muscle.

When in action some of them draw the lips upwards, others acting in an opposite direction pull them downwards, hence they are called levators and depressors respectively.

The orifice of the mouth is acted upon by a single muscle that encircles the lips (orbicularis oris), and when in action diminishes the size of the opening, as may be seen in the act of drinking. A similar muscle (orbicularis palpebrarum) surrounds the eyelids, which it closes.

Besides these there are others much larger and stronger, one forming-the anterior part of the cheeks (buccinator and caninus). These are attached to the upper and lower jaw, along the margins of the sockets which contain the fangs of the molar teeth. When in action they throw the food out of the channel of the cheek on to the grinding surface of the teeth.

Other muscles in this region are engaged in dilating the nostrils, and thus ministering to the function of respiration.

Name.

Origin.

Insertion.

Action.

Levator Palpebrae Superi-oris Externus.

From the external surface of the frontal bone.

Into the upper eyelid.

To raise the upper eyelid.

Orbicularis Palpebrarum.

Surrounds the eyelids. Arises from a small tubercle on the lachrymal bone.

Into the skin of the eyelids.

To close the eyelids.

Levator Palpebrae Superi-oris Internus.

From the bottom of the orbit behind the eye.

Into the upper eyelid.

To raise the upper lid.

Zygomaticus.

From the outer surface of the masseter muscle.

Into the angle of the mouth.

To retract the angle of the mouth.

Levator Labii Superioris Alaeque Nasi.

From the frontal and nasal bone.

Into the outer part of the nos-tril and the angle of the mouth.

To dilate the nostril and draw the angle of the mouth upwards.

Levator Labii Superioris.

From the malar and the superior maxilla or upper jaw-bone.

Joining the tendon of its fellow on the opposite side, it is inserted into the upper lip.

To elevate the upper lip and draw it to one side.

Dilator Naris Lateralis.

From the anterior part of the superior maxilla or upper jaw-bone.

Into the side of the nostril and upper lip.

To dilate the nostril and draw the upper lip backward.

Dilator Naris Anterior.

A small, single muscle attached to the front of the nasal cartilages.

To dilate the nostrils.

Depressor Labii Inferioris.

From the anterior border of the lower jaw behind the molar teeth.

To the skin of the lower lip.

To depress the under lip.

Name.

Origin.

Insertion.

Action.

Buccinator and Caninus.

Attached to the tuberosity of the superior maxilla, to the anterior border of the inferior maxilla behind the last molar tooth, and to the outer surface of the sockets of the molar teeth of the upper and lower jaw. Below it blends with the angle of the mouth.

To keep the food between the upper and lower molar teeth during mastication.

Orbicularis Oris.

Has no bony attachment.

Encircles the lips.

Closesthe lipsand assists in gathering the food, in drinking, and in mastication.

Dilator Naris Superioris.

From the side of the nasal peak.

Into the false nostril and the anterior turbinated bone.

To dilate the false nostril.

Dilator Naris Inferioris.

From the anterior and superior maxillary bones.

Into the cartilage at the anterior extremity of the posterior turbinated bone.

To dilate the false nostril.

Depressor Labii Superioris.

From the anterior maxillary bone above the upper incisor teeth.

Into the upper lip.

To depress the upper lip.

Levator Menti.

From the lower jaw beneath the incisor teeth.

Into the substance of the chin.

To raise the lower lip.