Ventral oblique

The ventral oblique muscle is a striated muscle of the orbit, part of the muscles of the eye. It originates in the fossa for ventral oblique muscle of the lacrimal bone. It runs laterally, passing ventrally along the eyeball to insert laterally.

Configuration: Orbital striated muscle

Origin: fossa for the ventral oblique muscle of the lacrimal bone

Insertion: Lateral part of eyeball

Relations: Ventral to eyeball, rostral to other muscles of the eye, ventrally covering insertion of ventral rectus muscle

Action: Eye extortion, elevation, abduction

Antagonist: Dorsal oblique muscle

Vascularization: Ventral branch of external ophthalmic artery, malar artery, ophthalmic plexus

Innervation: Ventral branch of the oculomotor nerve

Description:

The ventral oblique muscle is one of the striated muscles of the orbit.

It is the only muscle of the eyeball that does not originate at the apex of the orbit, and its origin lies on the medial wall of the orbit, marked by a fossa intended for it in the wall of the lacrimal bone. This fossa is ventromedial to the eyeball. The ventral oblique muscle runs laterally towards the eyeball, under which it passes ventrally, then reflects dorsally around it to attach to the lateral surface of the sclera. During its course, it passes ventrally over the insertion of the ventral rectus muscle and inserts close to the insertion of the lateral rectus muscle.

Contraction of this muscle triggers extorsion, elevation and abduction of the eye. The dorsal oblique muscle is antagonistic.

It is vascularized by the ventral muscular branch of the external ophthalmic artery, which may anastomose with an accessory branch of the malar artery. It is drained by veins forming part of the ophthalmic plexus.

It is innervated by the ventral branch of the oculomotor nerve. This nerve enters the orbit via the orbital fissure and reaches the caudal aspect of the muscle.

Variations:

In equids, the fossa serving as its origin is not very pronounced, and its insertion is near the ventral edge of the lateral rectus muscle.

In bovines, it originates just above the lacrimal bulla. Its wide aponeurosis inserts into the sclera ventro-laterally, close to the corneal limbus, and extends dorso-caudally under the rectus lateralis and retractor bulbi muscle, until close to the aponeurosis of the oblique dorsalis muscle.

In sheep, it attaches in the pre-equatorial region of the eyeball below the insertion of the lateral rectus muscle.

In pigs, it has a strong origin, attached to a deep pit in the orbital wall. Its insertion is thin, close to the corneal limbus.

In dogs, its insertion is perpendicular to the eyeball and is divided into two blades. One blade inserts rostrally at the insertion of the lateral rectus muscle, while the second passes under the insertion of the lateral rectus muscle and attaches to the sclera.

In cats, the aponeurosis is wide and divided, and inserts rostro-laterally and medially at the insertion of the lateral rectus muscle.

In rabbits, this muscle passes beneath the glandula profunda of the third eyelid. It inserts ventolaterally between the corneal limbus and the ventral edge of the lateral rectus muscle, with which it unites.

In men, this muscle is called the inferior oblique muscle. It originates on the orbital surface of the maxilla, near the infraorbital margin. It passes between the inferior wall of the orbit and the inferior rectus muscle. It inserts onto the inferotemporal quadrant of the posterior hemisphere of the eyeball.