Page:Encyclopædia Britannica, Ninth Edition, v. 1.djvu/875

Rh SKULL.] ANATOMY 825 which goes to the muscles of the face traverses a canal in the bone, called aqueduct of Fallopius, which ends ex ternally, between the styloid and mastoid processes, in the stylo-mastoid foramen. The styloid process is a slender part of the bone which projects downwards from the tympanic plate, and is connected with the small cornu of the hyoid bone by the stylo-hyoid ligament. It does not unite with the rest of the bone until a comparatively late period. Between the petrous -temporal and ex -occipital is the jugular foramen, which transmits out of the skull the eighth cranial nerve and the internal jugular vein. os of The fourteen bones of the Face are, as a rule, much face. smaller than those of the Cranium ; some have the form of thin scales, others are more irregular in shape. They are named as follows : Two superior maxillary, two palate, two malar, two nasal, two lachrymal, two inferior turbinal, a vomer, and an inferior maxilla. &amp;gt;er jaw. The Superior Maxilla?, or bones of the Upper Jaw (Figs. G and 7, and Plate XIV.), form the skeleton of a large part of the face, and enter into the formation of the walls of the cavities of the nose, mouth, and orbit ; around them the other bones of the face are grouped. The facial surface of each bone presents in front a large foramen for the transmission of the infra-orbital branch of the fifth cranial nerve, and behind, several small foramina for the trans mission of nerves to the teeth in the upper jaw. On the same surface is a rough process for articulation with the malar bone. The orbital surface is smooth, forms the floor of the orbit, and possesses a canal in which the infra- orbital nerve lies. The nasal surface forms a part of the outer wall and floor of the nostril, and presents a hole leading into a large hollow in the substance of the bone, called the ant rum, or superior maxillary air-sinus. The nasal surface articulates with the inferior turbinal and palate bones. The nasal and facial surfaces become con tinuous with each other at the anterior aperture of the nose, and from them a strong process ascends to join the frontal bone close to the glabella ; this process also articu lates with the lachrymal and nasal bones. The palatal surface forms a part of the bony roof of the mouth, and presents in front a small hole (the incisive foramen} which communicates with the nose. In the sheep and many other mammals this hole is of large size ; the palatal surface is bounded externally by a thick elevated border, in which are the sockets, or alveoli, for the lodgment of the fangs of the teeth; internally this surface articulates by a narrow border with the other superior maxilla and with the vomer, and, posteriorly, with the palate-bone. ate- The Palate-bone (Fig. 7, and Plate XIV.) lies in con- e - tact with the inner surface and posterior border of the superior maxilla, and separates it from the sphenoid. It is in shape not unlike the capital letter L, the horizontal limb forming the hinder part of the bony roof of the mouth by its lower surface, and the back part of the floor -of the nose by its upper. The ascending limb assists in forming the outer wall of the nose, and subdivides into an anterior, or orbital, and a posterior, or spJienoidal, pro cess. At the junction of the two limbs is the pyramidal process, which articulates with tho lower ends of the pteiygoid processes of the sphenoid. mer. The Vomer (Fig. 7), shaped like a ploughshare, lies vertically in the mesial plane of the nose, and forms a large part of the partition which separates one nostril from the other. It articulates above with the under surface of the body of the sphenoid and the mes-ethmoid ; below with the palatal processes of the superior maxillae and palate-bones ; in front with the septal cartilage of the nose, whilst the posterior border is free, and forms the hinder edge of the nasal septum. The Inferior Turbinated is a slightly convoluted bone situated on the outer wall of the nose, where it articulates Inferior with the superior maxilla and palate a little below the turbinatec! middle turbinal of the ethmoid. . The Lachrymal (Fig. 6) is a small scale-like bone, in Lachryma shape not unlike a finger-nail, placed at the inner wall of the orbit, and fitting between the ethmoid, superior maxilla, and frontal bones. It has a groove on the outer surface, in which is lodged the lachrymal sac. The Nasal (Fig. 6) is a thin, somewhat elongated Nasal. bone, which, articulating with its fellow in the middle line, forms with it the bony bridge of the nose ; above, it articulates with the frontal, and by its outer border with the ascending process of the superior maxilla. The Malar bone (Fig. 6), irregular in shape, forms the Malar, prominence of the cheek, and completes the outer wall of the orbit. It rests upon the superior maxilla ; by its orbital plate it articulates with the great wing of the sphenoid ; by its ascending process with the external angular process of the frontal ; by its posterior process with the zygomatic process of the temporal, so as to complete the zygomatic arch. The Inferior Maxilla, Lower Jaw, or Mandible (Figs. G and Mandible 7, and Plate XIV., fig. 9), is a large horse-shoe shaped bone, which has the distinction of being the only movable bone of the head. It consists originally of two separate halves, which unite during the first year of life into a single bone at the symphysis or chin. A characteristic feature ot the human lower jaw is the forward slope of the bone at the chin, for in other mammals the symphysis inclines backwards. In the upper border of this bone are the sockets for the lower series of teeth. At the posterior end of the horse-shoe curve on each side the bone ascends almost vertically, and terminates in two processes an anterior, or coronoid, which is for the insertion of the temporal muscle, and a posterior, or condyle, which is for articulation with the glen- oid fossa of the temporal bone. Where the ascending and horizontal limbs of the bone are continuous, it forms the angle, which is almost a right angle. On the inner surface of the ascending limb is a large foramen, communicating with a canal which traverses the bone below the sockets for the teeth. In this canal are lodged the nerves and blood-vessels for these teeth. The Hyoid bone lies in the neck, on the same plane as Hyoid. the lower border of the inferior maxilla (Figs. 6 and 7). It is shaped like the letter U, and consists of a body, or basi- hyal, from which two long horns, or stylo-hyals, project backwards. At the junction of the body and horns two smaller cornua, or cerato-hyals, project upwards, and are connected with the styloid processes of the temporal bones, or stylo-hyals, by the stylo-hyoid ligaments, or epi-liyals. The hyoid is the bone from which the muscles of the tongue arise, and it is situated immediately above the thyroid cartilage of the larynx, to which it is attached by ligaments. In its general form the Skull is ovoid, with the long General axis extending antero-posteriorly, the frontal and occipital form an&amp;lt; ^ ends rounded, and the sides somewhat flattened. Its S ! ze 1] of tlj average length in the people of the British Islands is a little more than 7 inches ; its greatest breadth about 5|- inches ; and its height, from the plane of the foramen magnum to the vertex, about 5| inches. Its greatest circumference is about 21 inches. The breadth of the face across the zygomatic arches is about 5 inches. The average capacity of the brain cavity is 92 cubic inches. The British skull is dolicho-cephalic and orthognathic. (See ANTHROPOLOGY.) The lateral regions of the skull are called the temporal fossae, and give origin to the temporal muscles. Under cover of each zygomatie arch is the zygomatic fossa. At the bottom of this is a hollow between the superior maxilla L 104