The angular series are four in number: viz. the zygomaticus major, levator anguli oris, risorius and depressor anguli oris. Two descend to the corner of the mouth obliquely from above, one runs almost horizontally forwards, and one ascends from below. They blend at the corner of the mouth, and form there a thick, muscular mass, behind which is a depression filled up with the fat covering the buccinator. In a lean face this depression is often very conspicuous, and in some faces its position is indicated by a dimple when the zygomaticus major contracts.

Zygomaticus major muscle

The zygomaticus major (French: muscle grand zygomatique) — named from its origin from the zygoma and its size — is ribbon-shaped and belongs to the first layer of the muscles.

Origin

The outer surface of the malar bone near the zygomatic suture.

Insertion

The deep surface of the skin and the subcutaneous tissue at the outer extremity of the upper lip, and just external to the commissure of the lips.

Structure

Arising by short tendinous fibers, the muscle forms a fleshy band which passes downwards and forwards to the meeting-point of the angular muscles at and external to the angle of the mouth, where it blends with the orbicularis oris and the other angular muscles, its outermost fibers passing into the outer fibers of the depressor anguli oris.

Nerve-supply

The infraorbital branch of the upper division of the facial nerve, which enters the middle of its deep surface.

Action

To draw upwards and outwards the corners of the mouth, as in smiling or laughter. When it is strongly contracted, it throws into prominence the soft parts of the cheek in front of the malar bone, raises the lower eyelid and produces 'crow's-feet,' as the wrinkles are called which radiate outwards from the outer canthus. When both muscles act together, the mouth is widened, and the upper lip raised so as to show the upper teeth, in what is called a ' broad grin.'

Relations

Superficially, the skin; deeply, the buccinator and facial part of the orbicularis oris, the facial and transverse facial arteries, the facial vein and some branches of the facial nerve.

Levator anguli oris muscle

The levator anguli oris — named from its action upon the corner of the mouth — is a triangular sheet and belongs to the second stratum of the facial muscles.

Origin

The canine fossa of the maxilla.

Insertion

The deep surface of the skin and the subcutaneous tissue, close to the corner of the mouth.

Structure

Arising muscular from its broad origin above the canine and bicuspid teeth, the fibers converge in a downward and outward direction, and blend with the other angular muscles outside the corner of the mouth.

Nerve-supply

The infraorbital branch of the upper division of the facial at the outer part of the anterior surface.

Action

To raise the corner of the mouth, but at the same time to draw it inwards.

Relations

Superficially, the zygomaticus minor and levator labii superioris, the infraorbital vessels and nerves; deeply, the facial portion of the orbicularis iris.

Risorius muscle

The risorius (french: muscle risorius) — named from its supposed action in laughter — is flat and ribbon-shaped, and belongs to the superficial sheet of muscles, being a part of the platysma myoides, and often very small and ill-developed.

Origin

The subcutaneous tissue overlying the deep fascia which covers the masseter and parotid gland.

Insertion

The subcutaneous and muscular tissue external to the angle of the mouth.

Structure

It is a band of parallel fibers which runs transversely forwards om the upper and posterior part of the platysma to the corner of the mouth.

Nerve-supply

The buccal branch of the lower division of the facial nerve which enters it from beneath.

Action

To widen the mouth by drawing its corner directly outwards. It is not used in the expression of pleasure like the zygomaticus major, but it gives a strained painful expression to the features, such as is seen in tetanus and called the 'risus irdonicus.'

Relations

Superficially, the skin and subcutaneous fat; deeply, the masseter and buccinator, the facial artery and vein, and branches of the facial nerve.

Depressor anguli oris

The depressor anguli oris — named from its action upon the corner of the rath — is a triangular sheet and belongs to the superficial layer of facial muscles.

Origin

The outer aspect of the lower border of the body of the mandible and tje external oblique line below the canine, bicuspid, and first molar teeth.

Insertion

The subcutaneous connective tissue and the muscular mass external the corner of the mouth.

Structure

Its fibers, arising fleshily, converge upwards and inwards, and having diminished to a narrow band, join the general muscular mass at the corner of the mouth, some of them being continued upwards into the levator anguli oris, and the most external into the zygomaticus major.

The fibers which form the inner border of the muscles are often continued downwards below the mandible, and form with those of the other side a band, partly muscular and partly fibrous, which, lying beneath the platysma myoides, supports and compresses the subcutaneous fat below and behind the prominence of the chin, then there is much subcutaneous fat, the absence of this support gives rise to a considerable prominence behind this band, and forms what is called a ' double chin.'

Nerve-supply

The supramaxillary branch of the lower division of the facial nerve, which sends filaments to the back part of its deep surface.

Action

To draw downwards and somewhat outwards the angle of the mouth, giving an expression of sorrow to the face, making the individual look 'down in the mouth.'

Relations

The skin superficially; deeply, the depressor labii inferioris and inferior coronary artery.