In contracting, the nasal portion of this muscle draws up the ala of the nose, espe cially its posterior and lower half; and as the cartilage and other dense tissues of this part do not admit of wrinkling, the muscle, in its full action, turns the nostril outwards, and expands its aperture at the same time that it wrinkles the skin above it.
3. Triangularis, (Cloquet, Bourgery, &c.; trunsversits, Santorini, Winslow, Theile; com pressor ?Iasi, Albinus, Haller; e,e, fig. 403) is a thin pale muscle whose origin is covered by the preceding. It arises by a narrow aponeurosis from the upper and outer part of the canine fossa, behind and extemal to the base of the ala of the nose. Its fibres thence diverge, the lower ones passing ahnost horizontally, the upper ones forwards and inwards, and they form a thin triangular muscle which covers the upper part of the ala of the nose and reaches to the dorsum. Sotnetimes many of its fibres pass over the dorsum of the nose and mingle with those of the muscle of the opposite side; but more often there intervenes between the two muscles a pliant fibro-cellular expansion, into the borders of which many of their fibres are inserted, and which thus forms a kind of me dian aponeurosis extending over the front of the nose and enabling both the muscles to act at once and equally upon it and the ala. In general, also, the upper or outer fibres of this muscle are continuous with those of the pyra midalis or are fixed in its aponeurosis; and the lower fibres are mingled with fibres of the de pressor aim nasi, and pass into the irregular assemblage of fibres beneath the skin of the lower border of the ala. Many of the fibres are connected through their whole course more or less intimately with the other tissues of the ala and the skin ; and probably it was from this last circumstance that Santorini was in duced to describe this muscle as having the whole of its origin among the fibres of the levator labii superioris akeque nasi, or mther as a muscle peculiar for having its middle por tion fixed (on the dorsum of the nose) and its two extremities moveable in the substance of each side of the upper lip.
These muscles have been described by some as compressors, by others as dilators of the nose, and in different circumstances they pro bably do act very differently. When the oute
or maxillary insertion of each is fixed, the assist in compressing the nostrils, and in com bination with the true depressors (presently t be described) their lower fibres draw the al backwards. When, on the other hand, the take their fixed point in the median aponeurosi on the dorsum of the nose, and contract toward it, those of their fibres which are connected with the skin will wrinkle it, as in the act of sneering, and those which are attached to the deeper tissues of the ala will draw it upwards and in some degree expand the nostril. When they compress the nostrils they commonly also draw backwards the apex of the nose in the manner usually seen in the act of smelling careful ly.
4. Depressor ale nasi, (Haller, Albinus, Theile ; illyrtiformis,seu pinnir dilatator, San torini; Petit dilatateur de Paile du nez, Baur gery ; ineisilmitoyen,Winslow; dilatator marlin'? , Arnold ; "fig. 403) arises by short appneurotie fibres from the alveolar margin above the se cond incisor and canine teeth of the upper jaw, below and on the inner side of the origin of the triangularis. Its fibres proceed upwards, forwards, and inwards, some going to the pos terior part of the skin under the sides of the septum, and many more to that of the al; manv of them, also, first rising, and then de scenilinc,r, form arches which are continued over the outer and posterior margin of the nostril, and are mingled with the fibres of the two preceding muscles, where they meet in the skin covering that part.
These muscles draw back and flatten the nostrils. Some of their fibres are mingled with those of the depressor labii superioris or su perior incisive muscle, and, whenever they act, the upper lip is fixed and somewhat elongated.
5. Depressor septi nariuni, or nasalis labii superioris, (Haller, Albinus; naso-labial, Hour gery; k, fig. 403 ;) may be regarded as a part of the upper portion of the circumference of the orbicularis oris, from which several fibres pro ceed forwards and inwards, converging from each side towards the septum of the nose. They are attached to the fibro-cellular tissue at the pos terior borders of the nostrils, and the middle fibres pass forwards under the septum between it and the skin of the columna, many of them extending nearly to the tip of the nose.