THE MAXILLAEY BONES. 149 



anterior palatine nerve and greater palatine artery. Its superior surface, 

 smooth and concave from side to side, forms the floor of the corresponding 

 nasal cavity. Its medial border, broad and serrated, rises in a ridge superiorly, so as 

 to form with its fellow of the opposite side the nasal crest, which is grooved 

 superiorly to receive the inferior 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. These parts support the septal cartilage of the nose. Immediately to the 

 lateral side of the incisor crest the superior surface of the palatine process is 

 pierced by a foramen which leads downwards, forwards, and a little medially, to 

 open into a broad groove on the medial border of the bone immediately behind 

 the central incisor tooth. When the two maxillae are articulated, the two grooves 

 form the oval foramen incisivum, into which the two afore-mentioned foramina open 

 like the limbs of a Y ; these are called the foramina of Stensen, and represent the 

 channels by which in lower animals the organs of Jacobson open into the mouth. 

 In man they afford a means of establishing an anastomosis between the vessels of 

 the mouth and nose. 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 palatine process, which is 

 sharp and thin, falls in line with the interval between the second and third molar, 

 and articulates with the horizontal part of the palate bone. 



Sinus Maxillaris. The maxillary sinus lies within the body of the bone, and 

 is of corresponding pyramidal form, its base being directed towards the nasal cavity, 

 with the middle meatus of which it communicates, its summit extending laterally 

 into the root of the zygomatic process. It is closed in anteriorly, posteriorly, and 

 above by the thin walls which form the anterior, infra -temporal, and orbital 

 surfaces of the body. Inferiorly it overlies the alveolar process in which the molar 

 teeth are implanted, more particularly the first and second, the sockets of which 

 are separated from it by a thin layer of bone. 



The angles and corners of this cavity are frequently groined by narrow ridges 

 of bone, one superiorly corresponds to the relief formed by the infra-orbital canal. 

 A vascular and nervous groove is often exposed, curving along the floor of the 

 maxillary sinus just above the alveoli of the teeth. The interior of the cavity is 

 lined by an extension from the mucous membrane of the nose. 



Connexions. The maxilla articulates with the nasal, frontal, lacrimal, and ethmoid 

 bones above, laterally with the zygomatic, and occasionally with the sphenoid, posteriorly 

 and medially with the palate, whilst on its medial side it unites with its fellow of the opposite 

 side, and also supports the inferior concha and the vomer. 



Ossification. The maxillae (proper) are developed in the connective tissue around 

 the oral aperture of the embryo. Ossification commences in membrane from one centre in 

 the neighbourhood of the canine tooth germ. From this centre growth takes place 

 rapidly in several directions, viz., upwards on the lateral side of the nasal capsule to form 

 the posterior part of the frontal process, backwards to form the zygomatic process, 

 downwards to form the lateral wall of the alveolar process, and medially to form 

 the palatine process. From the latter a process descends downwards on the medial 

 side of the teeth to form the medial wall of the alveolar process. At first a large gap 

 intervenes between the greater part of the palatine process and the zygomatic process, 

 but bridges of bone ultimately connect the two, separating the various tooth germs, 

 and so forming the tooth sockets. About the fourth month the maxilla invades a 

 small lateral cartilaginous process of the nasal capsule (Mihalkovics), and incorporates 

 it within itself. The infra-orbital nerve is at first placed considerably above the orbital 

 surface of the maxilla, and only comes in contact with it in the second month when 

 a groove is formed on the bone, which by the uprising of its lateral wall and its folding 

 over medialwards finally encloses the nerve and forms the infra-orbital canal and fora- 

 men. This account of the ossification of the maxilla, which differs considerably from 

 that given in previous editions, is based on the work of Mall and Fawcett. In the early 

 stages of the development of the bone the alveolar groove, in which the teeth are 



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