Connexions. — The nasal bones articulate with each other, with the frontal, ethmoid, and upper maxillary bones, and with the lateral cartilages of the nose : they form a part of the cavity of the nose.
Their structure is cancellous and thick above, thin and compact below.
Developement.—They are perfectly ossified at birth, when they are proportionally longer than in the adult, corresponding in this respect with the depth of the orbit and the smallness of the anterior aperture of the nose. The ossifica tion of each nasal bone commences by a single point about the beginning of the third month.
The lachrymal bones (ossa unguis v. lachry malia ; Germ. die Thriinenbeine) are qua drilateral in form, thin, semitransparent, and are situated on the anterior part of the inner wall of the orbit between the ethmoid, frontal, and upper maxillary bones ; they derive one of their names from the resemblance which they bear to a finger-nail. Each bone presents two surfaces and four borders.
The external or orbitar surface is divided at its anterior third by a vertical crest, terminating below in a little curved process which forms the outer wall of the upper orifice of the nasal canal; in front of this crest the bone is per forated with numerous little holes, and its sur face is concave and forms with that of the nasal process of the upper maxilla the canal for the lachrymal sac. The posterior part of this surface is smooth, nearly flat, and is continuous with that of the os planum of the ethmoid, which lies immediately behind it.
The internal or ethmoidal surface is rough, and is divided by a vertical groove, which corresponds to the crest on the orbitar aspect of the bone ; the anterior division is convex and forms part of the middle meatus ; the pos terior division is in contact with the ethmoid and contributes to close its cells.
Of the Arur borders, the superior is the shortest and thickest; it is irregular and arti culates with the inner border of the orbitar plate of the os frontis. The inferior is divided into two parts by the -lower extremity of the crest already described on the anterior surface of the bone; in front of this the border de scends along a thin process or angle of the bone, which is articulated with the inferior turbinated bone, and contributes to form the inner wall of the canal for the nasal duct ; behind, this border is broad, and rests on the inner margin of the orbitar plate of the upper maxillary bone. The anterior border is slightly grooved for the reception of the inner margin of the posterior border of the nasal process belonging to the upper maxilla. The posterior border is thin and articulates with the anterior edge of the os planum. The os unguis has four angles, of which the anterior inferior is remarkable for its length.
Connexions.—This bone articulates with the frontal, the upper maxillary, the ethmoid, and the inferior turbinated; it contributes to form part of the orbit of the cavity of the nose and of the groove for the lachrymo-nasal duct.
It gives attachment to the reflected portion of the tendon of the orhicularis palpebrarum, and to the tendon of the tensor tarsi muscles.
In structure it is thin and compact.
Development.—It is complete at birth, ex cept at its posterior superior angle, where there is a deficiency between it and the frontal and ethmoid bones, and where a separate piece is sometimes formed. It is broader from back to front in proportion, at this period of life, than in the adult, and its lachrymal groove is larger. Its ossification commences by a single point between the third and sixth months.
A small lachrymal bone has been described as sometimes found at the lower part of the os unguis; and not unfrequently some separate pieces are found at its angles, formed either front the ethmoid or from the orbitar plate of the upper maxillary bone.
The inferior turbinated bones,(ossaspongiosa v. turbinata infima ; Germ. die 'intern Muschel beine) of an oval form, thin and spongy in their appearance, are placed horizontally along the lower part of the outer wall of the nasal cavities, separating the middle from the inferior meatus, and contributing to increase the surface of the nose. Each hone presents two surfaces, two borders, and two extremities. The internal surfirce is rough, convex, and looks towards the septum of the nose, which it sometimes touches on one side when that partition inclines more than usually to the right or left. The external suryirce is concave, exhibiting many small fosse or pits ; it looks towards the upper maxilla and forms a part of the inferior meatus. Both surfaces are very irregular or spongy and are pitted by vessels, but especially by veins, which ramify abundantly upon them. The inferior border is convex and thick, particu larly at its centre, where it descends towards the floor of the nose. The upper border is thin and irregular, and presents from before backwards, 1. a thin edge, which is attached to the inferior turbinated crest on the nasal process of the upper maxilla; 2. a process (the lachrymal) which ascends towards the curved process of the os unguis, with which and with the adjacent part of the upper jaw-bone it unites to complete the canal for the nasal duct; 3. some irregular projections (ethawidal pro cesses) which ascend and unite with the ethmoid ; 4. a thin, eurled, dog's-ear-looking process (the auricular or maxillary), which, descending and overhanging the internal sur face of the bone, is attached to the lower part of the opening of the antrum, which it con tributes to circumscribe ; 5. an edge which is articulated with the inferior turbinated crest of the palate-hone. The orifice of the antrum is situated just above the centre of this border, and opens consequently into the middle mea tus.