|Henry Gray (18251861). Anatomy of the Human Body. 1918.|
|upper orifice of the incisive canal. The lateral border of the process is incorporated with the rest of the bone. The medial border is thicker in front than behind, and is raised above into a ridge, the nasal crest, which, with the corresponding ridge of the opposite bone, forms a groove for the reception of the vomer. The front part of this ridge rises to a considerable height, and is named the incisor crest; it is prolonged forward into a sharp process, which forms, together with a similar process of the opposite bone, the anterior nasal spine. The posterior border is serrated for articulation with the horizontal part of the palatine bone.|
Ossification.The maxilla is ossified in membrane. Mall 1 and Fawcett 2 maintain that it is ossified from two centers only, one for the maxilla proper and one for the premaxilla. These centers appear during the sixth week of fetal life and unite in the beginning of the third month, but the suture between the two portions persists on the palate until nearly middle life. Mall states that the frontal process is developed from both centers. The maxillary sinus appears as a shallow groove on the nasal surface of the bone about the fourth month of fetal life, but does not reach its full size until after the second dentition. The maxilla was formerly described as ossifying from six centers, viz., one, the orbitonasal, forms that portion of the body of the bone which lies medial to the infraorbital canal, including the medial part of the floor of the orbit and the lateral wall of the nasal cavity; a second, the zygomatic, gives origin to the portion which lies lateral to the infraorbital canal, including the zygomatic process; from a third, the palatine, is developed the palatine process posterior to the incisive canal together with the adjoining part of the nasal wall; a fourth, the premaxillary, forms the incisive bone which carries the incisor teeth and corresponds to the premaxilla of the lower vertebrates; 3 a fifth, the nasal, gives rise to the frontal process and the portion above the canine tooth; and a sixth, the infravomerine, lies between the palatine and premaxillary centers and beneath the vomer; this center, together with the corresponding center of the opposite bone, separates the incisive canals from each other.
FIG. 161 Anterior surface of maxilla at birth. (See enlarged image)
FIG. 162 Inferior surface of maxilla at birth. (See enlarged image)
Articulations.The maxilla articulates with nine bones: two of the cranium, the frontal and ethmoid, and seven of the face, viz., the nasal, zygomatic, lacrimal, inferior nasal concha, palatine, vomer, and its fellow of the opposite side. Sometimes it articulates with the orbital surface, and sometimes with the lateral pterygoid plate of the sphenoid.
Changes Produced in the Maxilla by AgeAt birth the transverse and antero-posterior diameters of the bone are each greater than the vertical. The frontal process is well-marked and the body of the bone consists of little more than the alveolar process, the teeth sockets reaching almost to the floor of the orbit. The maxillary sinus presents the appearance of a furrow on the lateral wall of the nose. In the adult the vertical diameter is the greatest, owing to the development of the alveolar process and the increase in size of the sinus. In old age the bone reverts in some measure to the infantile condition; its height is diminished, and after the loss of the teeth the alveolar process is absorbed, and the lower part of the bone contracted and reduced in thickness.
|5b. 3. The Lacrimal Bone|
The lacrimal bone, the smallest and most fragile bone of the face, is situated at the front part of the medial wall of the orbit (Fig. 164). It has two surfaces and four borders.
|Note 1. American Journal of Anatomy, 1906, vol. v. [back]|
|Note 2. Journal of Anatomy and Physiology, 1911, vol. xlv. [back]|
|Note 3. Some anatomists believe that the premaxillary bone is ossified by two centers (see page 299). [back]|