Levator labii superioris muscle

The levator labii superioris muscle in men, is worn directly in the upper lip. In domestic mammals, it deviates towards the nasal region, which it circumvents or even on which it stops.

Conformation: Its morphology varies accordingly. In humans, it is banded and almost straight. In carnivores, it is devoid of tendon and not very distinct from the canine muscle and will flourish between the upper lip and the wing of the nose. In ungulates and rabbits, it is formed of a thick, conoid fleshy body, which is continued rostrally by a tendon. Particularly long in equines, it will join on the tip of the nose that of the opposite side with which it forms an odd and banded expansion which descends between the two nostrils to under the skin of the upper lip. In cattle the arrangement is comparable to that of the angulates except for the tendon which separates at the upper edge of the muzzle, only a thin expansion is lost between the nostrils. In pigs the muscle becomes a levator of the snout in which it dissociates.

Insertions: It originates on the lateral face of the maxilla, at a variable level depending on the species. In humans and rabbits, its origin is not far from the infraorbital edge. In equines and pigs, the origin is similar but goes a little beyond the lacrimal bone. In ruminants it is just in front of the facial tubercle. In carnivores it is located a little below and behind the infraorbital foramen.

In humans and rabbits, the termination is at the deep surface of the orbicularis oris. In equines, it takes place on the superficial face of the latter, immediately under the skin, by median and odd fibrous expansion. In beef, the tendon ends in the muzzle more than in the upper lip. In pigs, it is located in the upper part of the snout. In the rabbit it terminates above and to the side of the philtrum.

Relations: In humans and rabbits, the origin is covered in part by the orbicularis oculi muscle. In equines the origin is covered by the malaris muscle. The fleshy body is covered largely by the levator nasolabialis muscle. Its ventral edge more or less overlaps the caninus muscle, except in equines, where the two muscles are completely separated. The deep surface is related to the maxilla and the infra-orbital vascular-nervous divisions.

Functions: This muscle raises and everts the upper lip, sideways if it acts alone and directly if it acts with the one on the opposite side. It lifts muzzle in beef and snout in pork. In the latter species it has only an indirect action on the upper lip.

Vessels and nerves: The levator labii superioris muscle is vascularized by the infraorbital artery and terminal branches of the facial artery. It is innervated by the dorsal buccal branch of the facial nerve.

Variation:

In equines, the levator labii superioris muscle comprises a thick, conoid fleshy body and a long tendon, which extends it rostrally. The fleshy body, lying on the side of the muzzle, originates not far from the infraorbital edge and obliquely crosses the levator nasolabialis muscle, which largely covers it.

In the ox, the  levator labii superioris muscle is weak, presenting a conoid fleshy body which originates with the caninus muscle, of which it covers the dorsal edge, just in front of the facial tubercle. It continues rostrally by a tendon which flattens and soon dissociates into several bundles; the medial fasciculus, flat and strongest, joins that of the opposite side and continues between the nostrils by a thin aponeurotic expansion which is lost under the glandular layer of the muzzle; the others will flourish in the dermis of the dorsal corner of the medial wing of the nostril.

In pigs, the levator labii superioris muscle is strong. Its fleshy body, thick, conical and penniform, originates under the orbit, in the entire caudal part of the canine fossa. It extends rostrally by a long and strong tendon which is carried to the upper edge of the snout and dissociates there into multiple fascicles, the most medial of which join those on the opposite side. A few fibrous bundles also descend to the snout bone, bypassing the nostril on the medial side. 

In dogs, the  levator labii superioris muscle is united to the canine muscle by its adjacent edges. They originate in common at the caudal part of the canine fossa, ventrally at the infra-orbital foramen. They are almost entirely covered by the levator nasolabialis muscle. The levator labii superioris muscle will develop on the side of the nostril and the canine in the upper lip to the deep side of the buccinator and orbicularis oculi muscles of the mouth

In the cat, the  levator labii superioris muscle and the caninus muscle are more distinct but weaker than in the dog, almost filiform. They are largely hidden by the orbicularis oculi muscle and the levator nasolabialis muscle.

In the rabbit, the  levator labii superioris muscle includes a conoid, bright red fleshy body, inserted very close to the infra-orbital edge and a tendon which ends at the tip of the nose, bypassing the nostril dorsally. It crosses the deep surface of the levator nasolabialis muscle.