The maxillary bone, (maxilla superior,) is very irregular. It presents an external convex surface, corresponding with the anterior and lateral parts of the face; another, internal, of considerable extent, corresponding with the nasal cavity ; one, superior, smooth, and inclined inwards, forming the floor of the orbit, and surmounted internally by a triangular process, forming the side of the nose ; lastly, a surface which projects horizontally inwards, to form the arch of the palate. The external surface is bounded inferiorly by a thick, dependent border (alveolar), for the lodgment of the teeth; to this as to a common point of union, all the other parts of the bone may be referred.
The alveolar border, thick, semicircular, and convex externally, concave internally, is pierced along its margin by a number of deep pits (alveoli), into which the teeth are inserted.
The pits or sockets vary in form and depth, conforming in these particulars to the roots of the teeth which they receive. From this border the external side ascends to the margin of the orbit, presenting some depressions and elevations; but at its fore part it is interrupted and excavated so as to present a deeply concave margin," which, with a similar one in the corresponding bone, forms the anterior nares.
This excavation is surmounted by a process, (ascending or nasal), prolonged as far as the frontal bone, with which it articulates.
The external surface of the nasal process, slightly grooved, gives attachment to the orbicularis palpebrarum muscle and the levator labii superioris alseque nasi. The internal, or nasal surface, somewhat concave presents a rough line, running from before backwards, which articulates with the inferior spongy bone ; above this is a depression corresponding with the middle meatus of the nose, and, towards the summit, a rough surface, which closes in the anterior ethmoidal cells. The anterior border is rough, for its attachment to the nasal bone; the posterior presents a well-marked groove, running from above downwards, and a little backwards with a slight curve, and which is completed into a canal by a similar one in the unguis bone, for the lachrymal sac.
The part of the external surface a little above the molar teeth is elevated into a rough projection, (malar process, eminence, tuberosity,) for its articulation with the malar bone. Anterior and inferior to this is observed a fossa, (fossa canina,) which gives attachment to the levator anguli oris. Between this fossa and the margin of the orbit is the infra-orbital foramen, which transmits the superior maxillary nerve. A little above the sockets of the incisor teeth is a slight depression, (myrtiform, or superior incisor fossa,) which gives attachment to the depressor muscle of the ala of the nose. Behind the malar tuberosity the surface is slightly excavated, and forms part of the zygomatic fossa; towards the posterior border it is plain, and forms one side of the spheno-maxillary fissure; and, at its junction with the orbital plate, it is rounded off and leads to the entrance of the infra-orbital canal. It terminates by a slight tuberosity, (tuber maxillare, 2 ) which projects behind the last molar tooth, and is perforated by a number of foramina, which transmit the superior dental nerves and arteries. The inner surface of its posterior border is rough, for its attachment to the tuberosity of the palate bone, and presents also a slight groove, contributing to the formation of the posterior palatine canal, which transmits the descending palatine branches from Meckel's ganglion.
From the upper border of the external surface, the orbital plate projects inwards, forming the floor of the orbit; its surface is smooth, being merely interrupted by the groove which leads to the infra-orbital canal; and at its inner and fore part, near the lachrymal groove, is a minute depression, which gives origin to the inferior oblique muscle of the eye. The infra-orbital canal commences behind on the surface of the orbital plate as a groove; becoming deeper in front and being changed into a complete canal, it opens on the anterior surface of the bone at the infra-orbital foramen, some distance below the margin of the orbit. It gives passage to a large nerve and an artery. In the interior of the bone a small canal leads downwards from the larger one, and conducts a nerve (anterior dental) to the front teeth.
The horizontal or palate plate of the bone projects inwards, forming the roof of the mouth and the floor of the nares. Its nasal surface is concave from side to side, and smooth; externally it is continuous with the body of the bone; internally it presents a rough surface, which is articulated with the corresponding bone, and surmounted by a ridge, 15 which completes the septum narium by articulating with the vomer and nasal cartilage; in front it is prolonged a little, so as to form a small process, 10 (anterior nasal spine); beside it is the incisor foramen, leading into the anterior palatine canal. The inferior surface of the palate plate which overhangs the mouth is arched and rough, and among the prominences of the surface it is slightly grooved for a large nerve which reaches the palate through the posterior palatine canal.
On examining with attention the large canal or fossa, named the anterior palatine, (in the skull,) it will be found that it contains four openings — two placed laterally, 1 a and two in the middle, one 4 before the other. The two former are described as the foramina of Steno (of Stenonis more properly) in many of the older anatomical works.
They are mentioned above as the "incisor" foramina. The others, which were first brought under notice by Scarpa, are placed in the intermaxillary suture, so that both maxillary bones contribute to form each of them. They are smaller than the preceding pair, from which they are separated by a very thin partition, and the lower orifice of the posterior one is larger than that of the anterior. It is through these median smaller canals (of Scarpa) that the naso-palatine nerves pass, — the nerve of the right side occupying the posterior one, and the nerve of the left side, the anterior.f
The body of the bone is hollowed into a large cavity, antrum High- mori, or maxillare, which in the fresh state is lined by mucous membrane and communicates with the middle meatus of the nose. Its orifice appears of great size in the dried bone when detached from its connexions, but it is considerably diminished when the contiguous bones are in their natural position, viz., the ethmoid, the inferior turbinate, and the palatal.
With the corresponding bone; with the frontal, by its nasal process; also with the ethmoid and os nasi; with the palate bone; with the malar, by the malar eminence ; with the os unguis, the vomer, the inferior spongy bone, and the nasal cartilage.
Attachments of muscles
Proceeding from below upwards; — above the border of the alveolar arch, the buccinator, and the depressor lahii superioris alseque nasi; to the canine fossa, the levator anguli oris and the compressor nasi; to the margin of the orbit, part of the levator labii superioris; to the nasal process, the orbicularis palpebrarum, and the common elevator of the lip and ala of the nose; and just within the orbit, the inferior oblique muscle of the eye.
The ossification of the upper maxillary bone begins at a very early period, — immediately after the lower maxilla and the clavicle, and before the vertebras. The facts hitherto ascertained with respect to its earliest condition are not adequate to determine the number of nuclei from which this bone is formed, or the manner of its growth.
If it is produced from several centers — and to this the balance of evidence inclines — the very early period at which the osseous deposit begins, and the rapidity of its progress over the bone, will account for the difficulty of marking the phases of change.
Beclard, whose opportunities of observing the growth of this and most other bones were considerable, states that he had found it to consist of four pieces, viz. 1. A palatal part, including all the palate except the incisor portion. 2. An orbital and malar division, comprising the parts implied by these names. 3. The nasal and facial connected. 4. The incisor piece, — being a small part of the palate behind the incisor teeth, and including in front the posterior margin of the alveolar border. But this anatomist adds, that he had not had the means of determining where the several pieces unite one to the other, and he admits that further observations of the bone at very early periods are necessary to determine the manner of its ossification.
Taking this bone when a single piece, it presents two fissures, one along the floor of the orbit; the other (the incisor groove) marking of a small portion of the palate behind the incisor teeth.
Now, the question arises, are these, the limits of ossification proceeding from different centers? There does not appear to be evidence that the first is so, for its presence may be owing solely to the construction of the canal over which it is placed. But with regard to the second, there are circumstances which would incline us to expect that the portion of bone it circumscribes should prove to be a distinct growth. The circumstances alluded to are the following: 1. The existence, in some cases of hare-lip, of a detached piece corresponding in its extent on the palate to the line of this fissure, and including the entire thickness of the alveolus with the incisor teeth. 2. The strictly defined extent of this piece: it never reaches beyond the line of the fissure — never includes a canine tooth. 3. No similar portion is ever found detached from another part of the upper or from the lower maxillary bone. 4. Lastly, may be added the existence of an inter-maxillary bone in animals with which an incisor piece in man would be analogous.
The foregoing facts render it probable that the incisor part is formed separately from the rest of the bone. Still, seeing that, except in cases of malformation, a distinct piece has not hitherto been clearly observed by any anatomist, and that the trace of separation which exists on the palate has never been found to extend to the anterior surface of the alveolus, it cannot be concluded that the part of the bone defined below by the incisor groove is ordinarily formed from a distinct center of ossification. In the present state of knowledge, therefore, the existence of an incisor bone in the human body at any period cannot be admitted.