THE MAXILLA 161 



of the nose, generally by two small apertures left between the above-mentioned 

 bones. In the fresh state, usually only one small opening exists, near the upper 

 part of the cavity; the other is closed by mucous membrane. On the posterior 

 wall are the alveolar canals, transmitting the posterior superior alveolar vessels 

 and nerves to the molar teeth. The floor is formed by the alveolar process of the 

 maxilla, and, if the sinus be of an average size, is on a level with the floor of 

 the nose; if the sinus be large it reaches below this level. 



Projecting into the floor of the antrum are several conical processes, correspond- 

 ing to the roots of the first and second molar teeth; 1 in some cases the floor is 

 perforated by the fangs of the teeth. The infraorbital canal usually projects into 

 the cavity as a well-marked ridge extending from the roof to the anterior wall; 

 additional ridges are sometimes seen in the posterior \vall of the cavity, and 

 are caused by the alveolar canals. The size of the cavity varies in different skulls, 

 and even on the two sides of the same skull. 2 



The Zygomatic Process (processus zygomaticus; malar process} .The zygomatic 

 process is a rough triangular eminence, situated at the angle of separation of the 

 anterior, zygomatic, and orbital surfaces. In front it forms part of the anterior 

 surface; behind, it is concave, and forms part of the infratemporal fossa; above, 

 it is rough and serrated for articulation with the zygomatic bone; while below, 

 it presents the prominent arched border which marks the division between the 

 anterior and infratemporal surfaces. 



The Frontal Process (processus frontalis; nasal process). The frontal process 

 is a strong plate, w r hich projects upward, medialward, and backward, by the side 

 of the nose, forming part of its lateral boundary. Its lateral surface is smooth, 

 continuous with the anterior surface of the body, and gives attachment to the 

 Quadratus labii superioris, the Orbicularis oculi, and the medial palpebral ligament. 

 Its medial surface forms part of the lateral wall of the nasal cavity; at its upper 

 part is a rough, uneven area, which articulates with the ethmoid, closing in the 

 anterior ethmoidal cells; below this is an oblique ridge, the ethmoidal crest, the 

 posterior end of which articulates with the middle nasal concha, while the anterior 

 part is termed the agger nasi; the crest forms the upper limit of the atrium of the 

 middle meatus. The upper border articulates with the frontal bone and the anterior 

 with the nasal; the posterior border is thick, and hollowed into a groove, which is 

 continuous below with the lacrimal groove on the nasal surface of the body: by 

 the articulation of the medial margin of the groove with the anterior border of 

 ihe lacrimal a corresponding groove on the lacrimal is brought into continuity, 

 ;ind together they form the lacrimal fossa for the lodgement of the lacrimal sac. 

 The lateral margin of the groove is named the anterior lacrimal crest, and is con- 

 tinuous below with the orbital margin; at its junction with the orbital surface is 

 a small tubercle, the lacrimal tubercle, which serves as a guide to the position of 

 :he lacrimal sac. 



The Alveolar Process (processus alvvolaris) . The alveolar process is the thickest 

 and most spongy part of the bone. It is broader behind than in front, and exca- 

 vated into deep cavities for the reception of the teeth. These cavities are eight 

 n number, and vary in size and depth according to the teeth they contain. That 

 r'or the canine tooth is the deepest; those for the molars are the widest, and are 

 subdivided into minor cavities by septa; those for the incisors are single, but 

 deep and narrow. The Buccinator arises from the outer surface of this process, 

 as far forward as the first molar tooth. When the maxillae are articulated with each 

 other, their alveolar processes together form the alveolar arch; the center of the 

 anterior margin of this arch is named the alveolar point. 



1 The number of teeth whose roots are in relation with the floor of the antrum is variable. The sinus "may extend 

 30 as to be in relation to all the teeth of the true maxilla, from the canine to the dens aapientice. " (Salter.) 



2 Aldren Turner (op. cit.) gives the following measurements as those of an average sized sinus: vertical height 

 opposite first molar tooth, 1}-^ inch; transverse breadth, 1 inch; and antero-posterior depth, 1}^ inch. 



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