Pyramidalis is situated between the brows, and may be considered as a prolongation of the inner fibres of the frontalis : it is of a triangular form ; its base above is continuous with the fibres of the frontalis; below it con tracts and is inserted into the aponeurotic ex pansion of the triangularis nasi. It is sepa rated from its fellow slip of the opposite side by a groove of cellular tissue.
Relations.—Its superficial surface adheres to the skin ; its deep one rests on the nasal eminence of the frontal bone, the nasal bones, and part of the lateral cartilage of the nose.
Use.—If this muscle acts at all on the nose, it is by drawing up the skin when the occipito frontalis is in action. Its more probable use is to give a fixed point to the frontalis, and to draw down the inner extremity of the brows and the skin between them.
Levator labii superioris aleeque fig. 134.) This is a thin, long, triangular muscle, placed nearly vertically on each side of the nose. It arises narrow from the outer surface of the nasal process of the upper max illary bone, immediately beneath the tendon of the orbicularis palpebrarum. It descends obliquely outwards, becoming broader, and terminates inferiorly by two slips, an internal short one, which is attached to the cartilage of the ala nasi, or to the fibrous membrane which invests it ; and an outer longer slip, which is attached to the skin of the upper lip near the nose, and mingles its fibres with the transversalis nasi, the levator labii superioris proprius, and the orbicularis oris.
Relations.—Covered by the skin, and over lapped a little above by the orbicularis pal-. pebrarum, this muscle covers the nasal process of the upper maxillary bone, the triangularis nasi, and the depressor alas nasi. Its inner border above corresponds to the pyramidalis.
Its action is to raise the ala of the nose and the adjacent part of the upper lip; in so doing it dilates also the nostril and becomes a muscle of inspiration. When strongly thrown into action, it corrugates the skin of the nose trans versely.
Triangularis nasi ( transversalis nasi, com pressor saris, Albin.) (n, fig. 134), is a very thin triangular muscle, placed transversely on the middle of the side of the nose. To expose its origin, the levators of the upper lip must be turned aside, and the skin of the nose very carefully dissected off. Its origin is then seen
as a narrow slip from the inner part of the canine fossa, below the ala nasi ; from this point the fibres radiate inwards and upwards, and expand into a very thin aponeurosis, which crosses the ala nasi and the lateral car tilage of the nose to be confounded along the median line with that of the opposite muscle, and with the pyramidalis. Bourgery describes two other origins, one superficial, attached to the skin below and to the outside of the ala nasi, and a middle one crossing and connected with the fibres of the levator of the upper lip.
lie/at/ans.—It is covered at its origin by the levator labii superioris alseque nasi, and inter nally by the integuments to which it super ficially adheres; it rests on part of the upper jaw, on the cartilages of the ala, and on the lateral cartilage.
Its action is yet undetermined by anato mists, some considering it a compressor or constrictor of the nose, others as a dilator or elevator. Cruveilhier thinks that its action varies with the form of the ala, which, when convex, makes it a compressor, when concave a dilator. Perhaps, as M. Bourgery suggests, its action depends upon which extremity is fixed, and that, when its base is fixed, its superficial fibres dilate the nostrils and draw the lip upwards and inwards, and that, when the muscle acts towards its maxillary attach ment, it compresses the nostril.
Depressor alr nasi (musculus tnyrtiforrnis), (fig. 134.) To expose this muscle the upper lip should be reversed, and the mucous mem brane divided on each side of the frwnum labii. It is a short flat muscle, radiating upwards from the myrtiform fossa of the upper jaw, where it arises towards the ala of the nose, into the posterior part of which it is inserted below and internal to the dilator nasi. This muscle really consists of two sets of fibres, one which has been just described, the other which is in front of this and is attached above to the ala and septum of the nose, below to the inner surface of the orbicular fibres. The first set, or the naso-maxillary fibres, are de pressors of the aim and contractors of the nostrils; the second, or naso-labial fibres, are elevators of the upper lip.