THE PREMAXILLiE 65 



The posterior extremity forms a rounded prominence, the maxillary tuberosity 

 (Tuber maxillare). Medial to the tuberosity is a deep recess (Recessus maxillaris), 

 in which are three foramina. The upper one, the maxillary foramen (Foramen 

 maxillare), leads into the infraorbital canal. The lower one, the posterior palatine 

 foramen (Foramen palatinum aborale), is the entrance to the palatine canal. The 

 sphenopalatine foramen (Foramen sphenopalatinum) perforates the inner wall of 

 the depression and opens into the nasal cavity. 



The zygomatic process (Processus zygomaticus) projects backward, dorso- 

 lateral to the tuberosity; it is overlapped by the corresponding part of the malar 

 and also articulates with the zygomatic process of the temporal. A small curved 

 plate (Processus temporalis) extends medially from it and joins the frontal and 

 palatine bones, forming part of the floor of the orbit. 



The palatine prpcess (Processus palatinus) is a horizontal plate which projects 

 from the lower part of the medial surface of the body. It forms the greater 

 part of the basis of the hard palate. Its nasal surface is smooth and is con- 

 cave transversely; on its anterior part, close to the medial border, there is a 

 shallow groove in which the vomero-nasal organ (of Jacobson) is situated. The 

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

 part the palatine groove (Sulcus palatinus); this is continuous at the anterior 

 palatine foramen (Foramen palatinum orale) with the palatine canal, and con- 

 tains the palatine vessels and nerve. The medial border unites with its fellow to 

 form the median palatine suture; its nasal aspect bears the nasal crest (Crista 

 nasalis), which forms, with that of the opposite process, a groove for the vomer. 

 The posterior border unites with the horizontal part of the palatine bone at the 

 transverse palatine suture. Variable accessory palatine foramina perforate the 

 process. 



The infraorbital canal (Canalis infraorbitalis)i extends almost horizontally 

 from the maxillary foramen 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 premaxilla, carrying 

 vessels and nerves to the teeth there. 



Development. — The maxilla ossifies in membrane ventral and lateral to the 

 cartilaginous nasal capsule. It has one chief center and a supplementary one in 

 the region of the deciduous canine tooth (Martin). 



The PREMAX1LL.E 



The premaxUIae (Ossa incisiva) form the anterior part of the upper jaw and 

 carry the incisor teeth. Each consists of a body, a nasal process, and a palatine 

 process. 



The body (Corpus) is the thick anterior part which carries the incisor teeth. 

 Its labial surface (Facies labialis) is convex and smooth, and is related to the upper 

 lip. The palatine surface (Facies palatina) is concave and often presents a foramen 

 a little behind its middle.^ The medial surface (Facialis medialis) is rough, and 

 joins the opposite bone; it is marked by a curved groove, which forms, with that on 

 the opposed surface, the foramen incisivum. The alveolar border (Limbus alveo- 

 laris) separates the palatine and labial surfaces ; it is curved and thick, and presents 

 three deep alveoli for the incisor teeth; behind the third alveolus it is free, forming 

 part of the interalveolar space. 



The nasal process (Processus nasalis) projects backward and upward from the 

 body, forming here the lateral wall of the nasal cavity. The two surfaces, facial 



' This is also known as the superior dental canal. 



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

 cisor. Smaller inconstant foramina are often present. 

 5 



