56 OSTEOLOGY. 



SUPERIOR MAXILLA. 



(Fig. 12. 8; Fig. 13. 14.) 



This is situated at the side of the face, and is the largest bone 

 of the upper jaw, very irregular in form, and elongated from 

 before backwards. It presents three surfaces, three borders, and 

 two extremities. 



The external or facial surface, concavo-convex in the adult, and 



somewhat convex in the young animal, is almost smooth, having 



an elongated horizontal ridge, the maxillary spine, continuous 



with the zygomatic spine of the malar bone, commencing opposite 



the third molar tooth, and running along the middle line of the 



posterior part of the surface. Near the middle of the upper surface 



is the large infra- orbital foramen, through which the facial division 



■of the fifth nerve and a branch from the superior dental artery 



pass. The inferior or palatine surface, slightly hollowed from 



side to side, consists of a bony plate, the palatine process, which 



forms the greater part of the bony palate, orpartition between 



the nasal fossae and the mouth ; it contains numerous small 



grooves and foramina, and one deep groove near its outer edge, 



the palatine, which is bounded by the alveolar processes of the 



molar teeth, and runs the whole length of the bone, giving 



passage to the palatine artery. The internal or nasal surface 



forms the sides and most of the floor of the nasal cavity ; it is 



irregularly concave, smooth, and divided into two concavities by 



.a longitudinal ridge, the internal maxillary spine, to which the 



inferior turbinal bone is attached. At the posterior part of this 



:surface is a large, deep excavation, the maxillary sinus, below 



which is a serrated surface, articulatingwith the palatine bone, 



and cantaining a fissure, which, with a corresponding fissure in 



the palatine bone, forms the palatine foramen. A little anterior 



to the sinus is the opening of the lachrymal conduit, which is 



continued by a shallow fissure to the anterior extremity of the 



bone ; along this conduit and fissure passes the lachrymal duct, 



which conveys the tears from the eye to the nasal chamber. 



The superior border is thin, convex, and divided into two 

 parts — an anterior, grooved and serrated for the attachment of 

 the external border of the nasal bone, and the inferior part of 

 the premaxilla, and a posterior, which is bevelled to articulate 

 -with the lachrymal and malar bones. The infemor border is 



