Lacrimal bone

At a glance

English

Lacrimal bone

Latin (TA2)

Os lacrimale

System

Bone

Region

Head

Side

Paired, left and right

About the lacrimal bone

The lacrimal bone is a thin, delicate scale of bone, about the size of a little fingernail, lying at the front of the medial wall of each orbit. It sits between the maxilla's frontal process in front and the orbital plate of the ethmoid behind, with the frontal bone above. Its chief role is in the tear drainage system: together with the maxilla it forms the hollow that holds the lacrimal sac and the start of the bony canal that leads tears down into the nose.

The posterior lacrimal crest, an upright ridge, splits its outer, orbital face. In front of the ridge runs a groove that, joined with a matching groove on the maxilla, completes the fossa for the lacrimal sac; the sac sits high in it, and below it narrows into the nasolacrimal canal. Behind the ridge the bone is smooth and simply carries on the orbital wall. Below, the crest ends in a little hook, the lacrimal hamulus, that curls forwards to meet the maxilla and close the upper opening of the canal. The lacrimal part of orbicularis oculi arises from the crest.

Its inner, nasal face has a furrow matching the outer crest. The part in front of the furrow faces into the middle meatus, while the part behind is applied to the ethmoid and closes off some of the anterior ethmoidal air cells. The four borders meet the maxilla, the ethmoid and the frontal bone, and the lower border sends a descending process down to the inferior nasal concha's lacrimal process, helping to enclose the nasolacrimal canal.

Being so thin, the bone breaks easily in injuries to the inner orbit or nose, and scarring after such fractures can block tear drainage and cause a watering eye. Surgeons open through it in dacryocystorhinostomy to make a new route from the tear sac into the nose. It ossifies from a single centre in membrane around the twelfth fetal week.

Function and supply

Function

Helps wall the passage that carries tears from the eye down into the inferior meatus of the nose.

Nerve supply

Not innervated as a muscle is; the nearby mucosa and skin are supplied by the infratrochlear branch of the nasociliary nerve and branches of the maxillary nerve.

Blood supply

Small periosteal branches from the anterior ethmoidal and angular arteries, with the infraorbital artery supplying the lower part.