|Position of the lacrimal bone (shown in green).|
|Medial wall of the orbit. Lacrimal bone is in yellow.|
|Gray's||subject #39 164|
The lateral or orbital surface is divided by a vertical ridge, the posterior lacrimal crest, into two parts.
In front of this crest is a longitudinal groove, the lacrimal sulcus (sulcus lacrimalis), the inner margin of which unites with the frontal process of the maxilla, and the lacrimal fossa is thus completed. The upper part of this fossa lodges the lacrimal sac, the lower part, the nasolacrimal duct.
The portion behind the crest is smooth, and forms part of the medial wall of the orbit.
The crest, with a part of the orbital surface immediately behind it, gives origin to the lacrimal part of the Orbicularis oculi and ends below in a small, hook-like projection, the lacrimal hamulus, which articulates with the lacrimal tubercle of the maxilla, and completes the upper orifice of the nasolacrimal canal; the hamulus sometimes exists as a separate piece, and is then called the lesser lacrimal bone.
The medial or nasal surface presents a longitudinal furrow, corresponding to the crest on the lateral surface.
Of the four borders:
- the anterior articulates with the frontal process of the maxilla;
- the posterior with the lamina papyracea of the ethmoid;
- the superior with the frontal bone.
- The inferior is divided by the lower edge of the posterior lacrimal crest into two parts:
- the posterior part articulates with the orbital plate of the maxilla;
- the anterior is prolonged downward as the descending process, which articulates with the lacrimal process of the inferior nasal concha, and assists in forming the canal for the nasolacrimal duct.
The lacrimal is ossified from a single center, which appears about the twelfth week in the membrane covering the cartilaginous nasal capsule.
In early lobe-finned fishes and ancestral tetrapods, the lacrimal bone is a relatively large and robust bone, running from the orbit to the nostrils. It forms part of the side of the face, between the nasal bones and the maxilla. In primitive forms, it is often accompanied by a much smaller septomaxilla bone, lying immediately behind the nasal opening, but this is lost in most modern species. The lacrimal bone is often smaller in living vertebrates, and is no longer always directly associated with the nasal opening, although it retains its connection with the orbit. The bone is entirely absent in living amphibians, as well as some reptilian species.1
In dinosaurs, the lacrimal bone usually defines the anterior rim of the orbit (eye socket), and the posterior rim of the antorbital fenestra. In some theropods (e.g. Allosaurus, Ceratosaurus, Albertosaurus) the upper part of the lacrimal bone grew in such a manner as to form a horn on the top of the dinosaur's head, usually situated above, and anterior to the eye. In many dinosaurs, the lacrimal bone comes into contact with the nasal bone, the jugal bone, the prefrontal bone, and the maxillary and premaxillary bones. The boundaries where some of these bones meet with the others are called sutures. Rarely, the lacrimal bones fused with the nasal bones to form a pair of "nasolacrimal" crests, which are present in dinosaurs such as Dilophosaurus, Megapnosaurus and Sinosaurus.2
|Wikimedia Commons has media related to Lacrimal bones.|
- Lacrimal+bone at eMedicine Dictionary
- Atlas of anatomy at UMich eye_5
- Atlas of anatomy at UMich rsa2p4
- Roche Lexicon - illustrated navigator, at Elsevier 34256.000-1
- Diagram at upstate.edu