Borders.-1. The anterior or naso-maxillary border is united above along the nasal process to the nasal bone. Below this it is thin and presents a deep semicircular notch, which forms the lateral and inferior portions of the anterior aperture of the nose. At the lower extremity of this notch the bone projects, and forms with its fellow of the opposite side the anterior nasal spine. The remainder of this border proceeds downwards and a little forwards to terminate on the alveolar border of the bone between the two middle incisor teeth.
2. The posterior or pterygo-palatine border, thick, rounded, and vertical, is united below to the palate bone, and above it forms, with the palate bone, the anterior border of the pterygo-maxillary fissure.
3. The bferior or alveolar border is thick and broad, especially behind, and forms about the fourth of an oval. It is perforated with conical cavities (alveoli) for the reception of the roots of eight teeth. These cavities are separated by thin transverse laminas. Tracing them backwards from the anterior extremity of the border, the orifices of the two first are nearly circular, and receive the incisors ; they are the largest, and are placed below the nasal notch. The third, in form transversely oval, receives the canine tooth, is of great depth, and ascends in front of the canine fossa. The fourth and fifth, also transversely oval, but not so deep, receive the lesser molar teeth ; they generally present ridges in their septa which correspond to grooves in the fangs of the teeth which are implanted into them.
The orifices of the three last cavities are quadrilateral, and receive the molar teeth. The sixth and seventh are subdivided into three lesser cavities, of which the two external are smaller than the inner one. Sometimes one of the molar teeth has four fangs, and then we find its socket subdivided into a cor responding number of cavities. The eighth alveolus, which receives the last molar tooth or dens sapientim, is not so distinctly divided into subordinate cavities, but presents ridges like the lesser molar. The outline of the alveolar border is waving, convex where it corresponds to the alveoli, and depressed op posite their septa. The whole of this border is covered by the gums, and presents innu merable pores for the nutritious vessels. The surfaces of the alveoli are also similarly marked.
Connexions.— The upper maxillary articu
lates with two bones of the cranium, viz. the ethmoid and frontal, and sometimes with the sphenoid by its pterygoid processes, or by an union of the orbitar plates of both bones at the outer extremity of the spheuo-maxillary fissure. In this case the malar bone does not enter into the formation of this fissure. The upper maxillary articulates with its fellow and with all the bones of the face. The me dian and lateral cartilages of the nose are at tached to it. It receives the upper teeth, and gives attachment to eight muscles, viz. the orbicularis palpebrarum, the inferior oblique of the eye, the levator labii superioris alxque nasi, the levator labii proprius, the depressor alas nasi, the compressor narium, the levator aoguli oris, and the buccinator ; often also to some of the fibres of the temporal and the external pterygoid muscles. It lodges the naso-palatine ganglion, and gives passage to the infra-orbitar and to the anterior and pos. tenor palatine and dental vessels and nerves. It forms the greater part of the sides of the nose, and of the floor of that cavity, and of the orbit, as well as of the roof of the mouth. It contains the maxillary sinus and the nasal duct.
Structure.—This bone is lighter than might be expected from its size, being occupied by the large antrum maxillare. It is cancellous only at the tuberosity, along the alveolar border, and at the malar and palatine processes.
Devtlopemen I.—The ossification of this bone commences as early as the thirtieth or thirty fifth day of foetal life, near its alveolar border, and it is complete at birth. It presents at this period, and often much later, two remark able fissures. 1. The incisive fissure, which may be traced from the alveolar border be tween the canine and lateral incisor tooth backwards and upwards, along the incisive canal towards the nasal process : it is sel dom observable on the facial surface of the bone. The part of the bone circumscribed by this fissure appears to correspond to the inter maxillary bone of animals, and is probably developed as a separate piece : it supports the incisor teeth. 2. A fissure is often found ex tending from the infra-orbitar groove forwards to the orifice of the canal. The existence of these fissures has led some anatomists to sup pose that the bone is developed by these ossific points.