THE PREMAXILL.E 



59 



greater part of the basis of the hard palate. Its superior or nasal surface is 



smooth and concave transversely; on its anterior part, close to the inner Ix^rder, 



is a shallow groove in which the organ of Jacobson is situated. The inferior or 



palatine surface is slightly concave from side to side, and presents along its outer 



part the palatine groove (Sulcus palatinus). The groove is a continuation of the 



palatine canal, and contains the palatine artery and nerve. The internal border 



unites with its fellow to form the 



median palatine suture; its nasal 



aspect bears the nasal crest, which 



forms, with that of the opposite 



process, a groove for the vomer. 



The posterior border unites with 



the horizontal part of the palate 



bone at the transverse palatine 



suture. 



The infraorbital or superior 

 dental canal extends almost hori- 

 zontally from the maxillary fora- 

 men to the infraorbital foramen. 

 It is placed at the upper edge of 

 the inner plate of the maxilla, 

 and traverses the maxillary sinus. 

 Near the infraorbital foramen it 

 gives off a small canal (Canalis 

 alveolaris incisivus) which lies 

 above the roots of the premolars 

 and extends also into the pre- 

 maxilla, carrying vessels and 

 nerves to the teeth there. 



Development. — The maxilla 

 ossifies in membrane below and 

 external to the cartilaginous nasal 

 capsule. It has one chief center 

 and a supplementary one in the 

 region of the deciduous canine 

 tooth (Martin). 





The Premaxillae 



The premaxillae (Ossa incis- 

 iva) form the anterior part of the 

 upper jaw and carry the incisor 

 teeth. Each consists of a body 

 and two processes, nasal and pala- 

 tine. 



The body is the thick an- 

 terior part which carries the in- 

 cisor teeth. Its labial or superior 

 surface is convex and smooth, and 

 is related to the upper lip. The 



palatine or inferior surface is concave and presents a foramen a little behind its 

 middle.' The internal surface is rough, and joins the opposite bone; it is marked 

 by a curved groove, which forms with that on the opposed surface, the incisive 



' This foramen is somewhat variable in position, but is commonly opposite the corner in- 

 cisor. Smaller inconstant foramina are often present. 



Fig. 31. — Upper J.\w of Horse About Four and a Half 

 Years Old, Ventral View. 

 1, 1, Po.sterior nares; 2, vomer; 3, horizontal part of 

 palate bone; 4, anterior palatine foramen; 5, palatine groove; 

 6, transverse palatine suture; 7, median palatine suture; 8, 

 palate process of maxilla; 9, palate process of premaxilla; 10, 

 foramen incisivum; 11, malar bone; 12, maxilla; 13, anterior 

 end of facial crest; 14, interalveolar space; I. 1-3, inci.sor 

 teeth; C, canine tooth; PI, first premolar or "wolf" tooth. 



