The cranial third of this part of the bone projects further mediad than does the rest of the medial border, forming thus the broad =palatine process=. This is rough on its medial edge for articulation with the premaxillary and the palatine process of the opposite bone. This medial edge rises also dorsally into a low ridge, the =nasal crest= (_m_), which is roughened for articulation with the vomer. The caudal two-thirds of the medial edge articulates with the palatine bone.
The cranial end of the bone articulates with the premaxilla.
The frontal process (_b_) presents on its inner surface, which looks into the nasal cavity, certain transverse ridges which are in relation with the ethmoid bone. Its outer surface is smooth. By its cranial border it articulates with the nasal bone dorsally and with the premaxillary bone ventrally.
[Illustration: FIG. 29.--PREMAXILLARY BONE, OBLIQUELY CRANIOLATERAL ASPECT.
_a_, the three incisor teeth; _b_, palatal portion of the bone; _c_, nasal process.]
Its dorsal end articulates medially with the nasal spine of the frontal bone, and caudally with the orbital plate of the same bone.
=Premaxillary Bone.= (=Os incisivum BNA.=) =Premaxilla= (Fig. 29).--The premaxillary bones bear the incisor teeth and form the cranial portion of the roof of the mouth.
Each consists of an irregular, horizontal =palatal portion= (_b_) and of a perpendicular =nasal process= (_c_) which forms part of the lateral boundary of the nares and enters into the formation of the lateral wall of the nasal cavity.
The palatal portion has in its caudal border a deep notch for the foramen incisivum or anterior palatine canal, which lies between it and the maxillary and transmits blood-vessels and nerves. It articulates with the maxillary bone by this border.
The medial border is raised into a thin crest of bone which, besides forming the medial wall of the foramen incisivum or anterior palatine canal, articulates by its medial border with the bone of the opposite side, forming a sort of median trough (=sulcus palatinus=) which projects dorsad into the nasal cavity and receives the ventral border of the nasal septum. The caudal end of this border articulates laterad with the maxilla, dorsad with the vomer.