44 LACHRYMAL BONES. 



By its external surface it gives attachment to the levator labii supe- 

 rioris alaeque nasi, and to the orbicularis palpebrarum muscle. Its 

 internal surface contributes to form the inner wall of the nares, and is 

 marked transversely by a horizontal ridge (crista turbinalis superior) 

 which divides it into two portions, one above the ridge irregular and 

 uneven, for giving attachment to and completing the cells of the la- 

 teral mass of the ethmoid ; the other below, smooth and concave, cor- 

 responding with the middle meatus. The posterior border is thick 

 and hollowed into a groove for the nasaL duct. The margin of the 

 nasal process, which is continuous with the lower border of the orbit, 

 is sharp and marked by a small tubercle which serves as a guide to 

 the introduction of the knife in the operation for fistula lachrymalis. 



The malar process, large and irregular, is situated at the angle of 

 separation between the facial and zygomatic surfaces, and presents a 

 triangular surface for articulation with the malar bone. 



The alveolar process forms the lower margin of the bone ; it is 

 spongy and cellular in texture, and excavated into deep holes for the 

 reception of eight teeth. 



The palate process is thick and strong, and projects horizontally 

 inwards from the inner surface of the body of the bone. Superiorly, 

 it is concave and smooth, and forms the floor of the nares ; inferiorly, 

 it is also concave but uneven, and assists in the formation of the roof 

 of the palate. This surface is marked by a deep groove, which lodges 

 the posterior palatine nerve and artery. Its internal edge is raised 

 into a ridge (crista nasalis), which, with a corresponding ridge in the 

 opposite bone, forms a groove for the reception of the vomer. The pro- 

 longation of this ridge forwards beyond the level of the facial surface 

 of the bone is the nasal spine. At the anterior extremity of its nasal 

 surface is a foramen, which leads into a canal formed conjointly by 

 the two superior maxillary bones, the anterior palatine canal. The 

 termination of this canal is situated immediately behind the incisor 

 teeth, hence it is also named the incisive foramen. Associated with 

 the incisive openings and canal are two smaller canals, the naso-pala- 

 tine, which transmit the naso-palatine nerves. These canals are 

 situated in the walls of the incisive canal, and terminate inferiorly in 

 that canal, either by separate openings or conjoined. 



Development. By four centres ; one for the anterior part of the 

 palate, and incisive portion of the alveolar process (the permanence of 

 this piece constitutes the intermaxillary bone of animals) ; one for that 

 portion of the bone lying internally to the infra-orbital canal and fora- 

 men ; one for that portion lying externally to the groove and canal ; 

 and one for the palate process. The superior maxillary bone is one of 

 the earliest to shew signs of ossification, this process beginning in the 

 alveolar process, and being associated with the early development of 

 teeth. The early development of the alveolar process, and the conse- 

 quent fusion at this point of the original pieces, explains the diffi- 

 culties which have been felt by anatomists in determining the precise 

 number of the ossifying centres. 



