By the contraction of this muscle, the lip is raised, on one side only, if a single muscle contracts, or in its whole extent, if the two muscles act simultaneously.
=Internal Elevator (or Superficial) of the Upper Lip and the Wing of the Nose= (_levator labii superioris alæque nasi_) (Fig. 90, 6; Figs. 91, 92).--This is the muscle veterinarians designate _the supranaso-labial_.
Arising from the frontal and nasal bones, it thence passes towards the upper lip, where it is inserted as well as into the wing of the nose.
In the ox it is united above with the frontal muscle, and below is divided into two fasciculi, between which pass the elevator described above and the canine muscle.
In the horse it is also divided into two fasciculi; but the arrangement is the opposite as regards, their relations with neighbouring muscles, in this animal and in the preceding.
In the ox the external fasciculus is covered by the external elevator and the canine, which pass under the internal fasciculus; in the horse the deep elevator passes under the two fasciculi, and the canine passes under the external bundle, and afterwards covers the internal.
In the pig, the internal elevator is wanting.
As its name indicates, it raises the upper lip and the wing of the nose.
=Transversus Nasi.=--In the horse this muscle, which is very thin, is situated on the dorsum of the nose, and proceeds to be inserted into the cartilaginous skeleton of the nostrils. In the pig, it occupies an analogous situation. It does not exist in the ox or in carnivora. The transversus nasi is a dilator of the nostrils.
[Illustration: FIG. 92.--MYOLOGY OF THE HORSE: MUSCLES OF THE HEAD.
1, Masseter; 2, orbicularis palpebrarum; 3, zygomaticus major; 4, lachrymal (this muscle is sometimes described under the name of the small zygomatic); 5, external elevator (or deep) of the upper lip and ala of the nose; 6, internal elevator (or superficial) of the upper lip and of the ala of the nose; 7, levator anguli oris or caninus; 8, orbicularis oris; 9, buccinator; 10, maxillo-labialis; 11, zygomatico-auricularis; 12, temporo-auricularis externus; 13, cervico-auricularis; 14, parotid gland; 15, parotido-auricularis; 16, inferior maxillary bone.]