THE SUPERIOR MAXILLARY BONES. 85 



the upper jaw. From the back part of the infraorbital canal a second small 

 canal is sometimes given off, which runs downward in the outer wall of the 

 antrum, and conveys the middle dental nerve to the bicuspid teeth. Occasion- 

 ally this canal is derived from the anterior dental. At the inner and fore part 

 of the orbital surface, just external to the lachrymal groove for the nasal duct, is 

 a depression which gives origin to the Inferior oblique muscle of the eye. 



The internal surface (Fig. 50) is unequally divided into two parts by a hori- 

 zontal projection of bone, the palate process : the portion above the palate process 

 forms part of the outer wall of the nasal fossae ; that below it forms part of the 

 cavity of the mouth. The superior division of this surface presents a large, irreg- 

 ular opening leading into the antrum of Highmore. At the upper border of this 

 aperture are numerous broken cellular cavities, which in the articulated skull are 

 closed in by the ethmoid and lachrymal bones. Below the aperture is a smooth 

 concavity which forms part of the inferior meatus of the nasal fossae, and behind 

 it is a rough surface which articulates with the perpendicular plate of the palate 

 bone, traversed by a groove which, commencing near the middle of the posterior 

 border, runs obliquely downward and forward, and forms, when completed by its 

 articulation with the palate bone, the posterior palatine canal. In front of the 

 opening of the antrum is a deep groove, converted into a canal by the lachrymal 

 and inferior turbinated bones. It is called the lachrymal groove, and lodges the 

 nasal duct. More anteriorly is a well-marked rough ridge, the inferior turbinated 

 crest, for articulation with the inferior turbinated bone. The shallow concavity above 

 this ridge forms part of the middle meatus of the nose, while that below it forms 

 part of the inferior meatus. The portion of this surface below the palate process 

 is concave, rough and uneven, and perforated by numerous small foramina for the 

 passage of nutrient vessels. It enters into the formation of the roof of the mouth. 



The Antrum of Highmore, or Maxillary Sinus, is a large, pyramidal cavity 

 hollowed out of the body of the maxillary bone : its apex, directed outward, is 

 formed by the malar process ; its base, by the outer wall of the nose. Its walls 

 are everywhere exceedingly thin, and correspond to the orbital, facial, and zygo- 

 matic surfaces of the body of the bone. Its inner wall, or base, presents, in the 

 disarticulated bone, a large, irregular aperture, which communicates with the 

 nasal fossa. The margins of this aperture are thin and ragged, and the aperture 

 itself is much contracted by its articulation with the ethmoid above, the inferior 

 turbinated below, and the palate bone behind. 1 In the articulated skull this cavity 

 communicates with the middle meatus of the nasal fossae, generally by two small 

 apertures left between the above-mentioned bones. In the recent state usually 

 only one small opening exists, near the upper part of the cavity, sufficiently large 

 to admit the end of a probe, the other being closed by the lining membrane of 

 the sinus. 



Crossing the cavity of the antrum are often seen several projecting laminae of 

 bone, similar to those seen in the sinuses of the cranium ; and on its posterior wall 

 are the posterior dental canals, transmitting the posterior dental vessels and nerves 

 to the teeth. Projecting into the floor are several conical processes, corresponding 

 to the roots of the first and second molar teeth ; 2 in some cases the floor is perfo- 

 rated by the teeth in this situation. 



It is from the extreme thinness of the walls of this cavity that we are enabled to explain 

 how a tumor growing from the antrum encroaches upon the adjacent parts, pushing up the floor 

 of the orbit, and displacing the eyeball, projecting inward into the nose, protruding forward on 

 to the cheek, and making its way backward into the zygomatic fossa and downward into the 

 mouth. 



The Malar Process is a rough, triangular eminence, situated at the angle of 



1 In some cases, at any rate, the lachrymal bone encroaches slightly on the anterior superior por- 

 tion of the opening, and assists in forming the inner wall of the antrum. 



2 The number of teeth whose fangs are in relation with the floor of the antrum is variable. The 

 antrum " may extend so as to be in relation to all the teeth of the true maxilla, from the canine to 

 the dens saptentue." (See Mr. Salter on Abscess of the Antrum, in a System of Surqery, edited bv T. 

 Holmes, 2d ed. vol. iv. p. 356.) 



