THE SKULL. 41 
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. 
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 (4) 
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 rye, 29. — pre. 
maxillary and transmits blood-vessels and nerves. : Reroagi se 
It articulates with the maxillary bone by this iquery Cra- 
border, eee 
The medial border is raised into a thin crest a, the three in. 
of bone which, besides forming the medial wall of SO saree a 
the foramen incisivum or anterior palatine canal, the bone; ¢, nasal 
articulates by its medial border with the bone of P™°°** 
the opposite side, forming a sort of median trough (sulcus pala- 
tinus) 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 maxil- 
lary bone. 
