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. Its craniolateral border bears the incisor teeth (_a_). The nasal process (_c_) presents three surfaces, all elongated and triangular; one, the medial surface, is smooth and concave and looks into the nasal cavity. Its dorsal border is rough for articulation with the nasal bone dorsad, and smooth ventrad where it aids in forming the nares. The lateral surface is smooth. The caudal surface is rough for articulation with the maxillary bone. =Nasal Bone.= =Os nasale= (Fig. 30).--The nasal bones fill the space between the nasal process of the premaxillary, the frontal process of the maxillary, and the nasal spine of the frontal bone (Fig. 39, 7). They thus form part of the dorsal wall of the nasal cavity near the middle line. [Illustration: FIG. 30.--NASAL BONE, DORSAL VIEW.] Each may be described as consisting of two elongated triangular lamellæ, one vertical, the other horizontal. The vertical lamella is curved slightly ventrad and has its apex directed craniad. It is applied by its medial surface against the vertical lamella of the opposite bone, the two thus forming a median vertical partition, the =nasal crest= (Fig. 43, 12), which extends ventrad into the nasal cavity and, by joining the dorsal edge of the lamina perpendicularis, helps to form the internasal septum. The horizontal lamella is attached to the dorsal margin of the vertical lamella in such a way that its apex lies opposite the base of the vertical lamella. It helps to roof in the nasal cavity, and by its base forms a part of the dorsal boundary of the narial opening. By its lateral margin it articulates with the nasal spine of the frontal at its caudal end, with the frontal process of the maxillary at its middle, and with the nasal process of the premaxilla at its cranial end. The lateral angle of its base projects in a curved line which forms the dorsal part of the lateral boundary of the narial opening. From the lateral border of the horizontal lamella a bony plate curves ventrad and mediad, enclosing a narrow fossa which receives a part of the ethmoid. This is the =concha nasalis superior= (nasoturbinal bone). =Ethmoid Bone.= =Os ethmoidale= (Figs. 31 and 32).--The ethmoid bone closes in the cranial cavity at its cranial end and extends forward into the nasal cavity, which it largely fills.