These small bones are named " ungual" from a resemblance, if not in form, at least in thinness and size, to a finger-nail (unguis); they are also called the " lachrymal" bones, from their presenting each a groove, which, with a similar excavation in the nasal process of the superior maxilla, forms the lachrymal canal.
Placed at the inner and anterior part of the orbit, the os unguis presents two surfaces and four borders; its external or orbital surface, plain in the greater part of its extent, is hollowed anteriorly by a groove which runs from above downwards, and contributes, as above stated, to lodge the lachrymal sac. Part of the internal surface, which is rough, corresponds with the anterior ethmoidal cells, the rest with the middle meatus narium. The superior border is articulated with the orbital process of the frontal bone; the interior with the superior maxillary bone; and where it dips down, to form a part of the lachrymal canal, it joins the inferior spongy bone; anteriorly, it rests on the nasal process of the superior maxillary bone, and posteriorly 5 on the os planum of the ethmoid.
Each unguis bone is developed from one osseous center, which is apparent shortly after the ossification of the vertebras is begun.