In old age the vertical diameter of the face decreases in consequence of the loss of the teeth and the contraction of the alveolar borders of the jaws, which touch each other when the mouth is closed; the mini of the jaw resume the oblique direction of childhood, (fig. 133;) and the symphysis inclines from the shrunken alveolar border downwards and forwards to the base of the bone, and gives to the chin the projecting appearance which is so character istic of this period of life.
The articulations of the face comprise those of the upper and that of the lower jaw.
The articulations of the bones of the upper jaw with each other and with those of the cra nium are all of the kind called suture, but they present considerable variety in the extent, form, and adaptation of their articular surfaces. Those bones of the face which contribute to form its columns of support, and to which this part of the head owes its strength and resistance to violence, have their articular surfaces for the most part broad and rough, presenting emi nences and depressions which are adapted to those of the contiguous bone; examples of this firm articulation are seen, 1. at the anterior part of the intermaxillary suture, where the two palatine plates unite and form the horizontal column or base of the upper jaw ; 2. at the nasal columns, where the nasal bones and the nasal processes of the upper maxilla' unite with the frontal ; 3. on the sides of the face, or where the bones form their lateral or malar columns, viz. at the jugo-maxillary and jugo frontal articulations. The spheno-jugal articu lation, seen within the orbit, and the zygomatic or temporo-jugal, though formed by the union of comparatively narrow surfaces or borders, derive strength from their irregularity, and, in the case of the zygomatie suture, from its in dented form, which maintains its security from vertical blows, as the curved direction of the zygoma protects it from lateral injury.
Those sutures of the face. which are, strictly speaking, harmonic, are such as are not exposed to any considerable pressure ; they present, nevertheless, some varieties in their mode of juxtaposition. In some the adaptation is direct, as in the pterygo-palatine. In others one horder or surface is received by another (schindylesis), as in the articulations of the vomer with the sphenoid above, and with the groove in the palatine plates of the upper max illary and palate bone inferiorly. Sometimes
the surfaces are simply applied against each other, as the nasal plate of the palate bone on the nasal surface of the upper maxillary. Lastly, the edges may alternately overlap each other, as those of the nasal and upper maxillary bones.
In all the sutures of the face, whatever may be the adaptation of the osseous surfaces, we find interposed a thin layer of cartilage uniting the contiguous surfaces of the bones. This is easily shown in some of the sutures by mace ration, and only disappears in places as some of the bones become united with advancing age.
The great number of pieces of which the upper jaw consists, and the varying form and direction of the sutures, all contribute, with the figure of the bones themselves, to give strength to this part of the skull, and to break the force of blows by diffusing them over a widely ex tended surface.
The sutures of the face derive their names from the bones which contribute to form them; thus we have between the orbits the fronto nasal, fronto-maxillary, and fronto-lachrymal sutures, all contributing to form part of the transverse suture. (See CRANIUM.) Lower down we find the nasal, the naso-maxillary, and the lachrymo-maxillary, which turns at right angles backwards along the inner wall of the orbit into the ethmoido-maxillary and pa lato-orbitar sutures. On the outer side of the orbit may be observed the fronto-jugal and spheno-jugal sutures ; on the zygomatic arch the temporo-jugal suture; and below the pro minence of the cheek, the jugo-maxillary suture, which is seen both on the anterior and posterior surface of the upper jaw. On the roof of the mouth are seen the longitudinal and the transverse palatine sutures, the former formed by the intermaxillary in front, and by the inter-palatine suture behind : the latter is often termed the transverse or horizontal palato maxillary suture. There are some other sutures within the nose which it is unnecessary to enu merate.
The lower jaw articulates with the cranium by diarthrosis : this important joint will be particularly described in the article TEM rono MAXILLARY ARTICULATION.
The bones of the face are invested with periosteum or a fibrous membrane, which is variously modified and arranged in the orbits, nose and mouth, &c.