The =premaxillæ= (Ossa incisiva) form the anterior part of the upper jaw
and carry the incisor teeth. Each consists of a body and two processes,
nasal and palatine.
The =body= is the thick anterior part which carries the incisor 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.[15] 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
=foramen= (Foramen incisivum). The =alveolar border= (Limbus alveolaris)
separates the palatine and labial surfaces; it is curved and thick, and
presents three alveoli for the incisor teeth; behind the third alveolus
it is rounded and 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= and =nasal=, are smooth and rounded. The
=superior border= is free, thick, and smooth. The =inferior border= is
dentated and joins the maxilla; at its anterior end it forms with the
latter the alveolus for the permanent canine tooth.[16] The =posterior
extremity= fits into the interval between the nasal bone and the
maxilla.
The =palatine process= (Processus palatinus) is a thin plate which forms
the anterior part of the basis of the hard palate. Its =nasal= or
=superior surface= has a longitudinal ridge which forms with that of the
other side a groove for the septal cartilage. The =palatine= or
=inferior surface= is flat. The =internal border= is serrated and meets
its fellow at the median palatine suture. The =external border= is
separated from the maxilla and the nasal process by the =palatine cleft=
(Fissura palatina). The =posterior extremity= fits into the interval
between the vomer and the palatine process of the maxilla.
=Development.=—The premaxilla ossifies from a single center. Fusion of
the two bones is complete at the end of the third or the beginning of
the fourth year.