In the horse it arises below the orbital cavity; then, after having crossed the superficial elevator, it ends in a tendinous expansion, situated in the median line between the nasal fossæ. This expansion divides into fasciculi, which end in the thickness of the upper lip.
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.