130 OSTEOLOGY. 
horizontal plane; it has two surfaces-—upper and under—and three borders, a straight 
internal, a more or less straight posterior, and a curved external, by which latter 
it is attached to the inner side of the body and alveolar process as far back as the 
interval between the second and third molar teeth. Its under surface, together 
with that of its fellow, forms the anterior three-fourths of the vaulted hard palate ; 
it is rough and pitted for the glands of the mucous membrane of the roof of the 
mouth, and is grooved on either side near the alveolar margin by a channel which 
passes forward from the posterior palatine canal and transmits the great palatine 
nerve and descending palatine artery. Its superior surface, smooth and concave 
from side to side, forms the floor of the corresponding nasal fossa. Its internal or 
mesial border, broad and serrated, rises in a ridge superiorly, so as to form with its 
fellow of the opposite side the nasal crest (crista nasalis), which is grooved superiorly 
to receive the lower border of the vomer. In front of its articulation with the 
vomer this ridge rises somewhat higher, being named the incisor crest, anterior to 
which it projects beyond the free border of the nasal notch, and together with its 
fellow forms the pointed projection called the anterior nasal spine (spina nasalis 
anterior). These parts support the septal cartilage of the nose. Immediately to 
the outer side of the incisor crest the superior surface of the palatal process is 
pierced by a foramen which leads downwards, forward, and a little immwards, to open 
into a broad groove on the mesial border of the bone immediately behind the 
central incisor tooth. When the two maxille are articulated, the two grooves 
form the oval anterior palatine canal or fossa, into which the two aforementioned 
foramina open like the limbs of a Y; these are called the incisor foramina or the 
foramina of Stenson, and contain the remains of Jacobson’s organs. In front and 
behind these, and lying within the fossa and in the line of the suture, are the 
smaller foramina of Scarpa, which transmit the naso-palatine nerves, the right nerve 
usually passing through the posterior foramen, the left through the anterior. The 
posterior border of the palatal process, which is sharp and thin, falls in line with 
the interval between the second and third molar, and articulates with the horizontal 
plate of the palate bone. 
The maxillary sinus or antrum of Highmore (sinus maxillaris) lies within the 
body of the bone, and is of corresponding pyramidal form, its base being directed 
towards the nasal fossa, with the middle meatus of which it communicates, its 
summit extending outwards into the root of the zygomatic process. It is closed 
in externally and above by the thin walls which form the facial, zygomatic, and 
orbital surfaces of the body. Inferiorly it overlies the alveolar process in which 
the molar teeth are implanted, the sockets of which are separated from it by a thin 
layer of bone. 
Advantage is taken of this circumstance to pierce the floor of the antrum in such conditions 
as necessitate its thorough drainage, as its natural outlet into the middle meatus is of the nature 
of an overflow aperture, and so prevents purulent fluids, which may here accumulate, from being 
readily discharged. 
The angles and corners of this cavity are frequently groined by narrow ridges 
of bone, and the interior is lined by an extension from the mucous membrane of 
the nose. 
Connexions.—The superior maxillary bone articulates with the nasal, frontal, lachrymal, 
and ethmoid bones above, externally with the malar, and occasionally with the sphenoid, 
posteriorly and internally with the palate, whilst on its inner side it unites with its fellow of 
the opposite side, and also supports the inferior turbinated bone and the vomer. 
Architecture.—The disposition of the maxillary sinus within the body of the bone has been 
already referred to. In union with its fellow, the vaulted arrangement of the hard palate is well 
displayed, and the arched arrangement of the superior alveolar processes is obvious. It is in 
these latter processes around the sockets for the reception of the teeth that the cancellous tissue 
of the bone is seen; elsewhere its walls are formed by thin and dense bone. 
Variations.—Not unfrequently there is a suture running vertically through the bar of bone 
which separates the infraorbital foramen from the infraorbital margin. Through imperfections 
in ossification the infraorbital canal may form an open groove along the floor of the orbit. 
Ossification.—The superior maxille are developed in the connective tissue around 
the oral aperture of the embryo. The centres from which the bone ossifies are not 
preceded by a cartilaginous stage. Their number is uncertain, as early fusion occurs 
