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 (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 FIG. 29. PRE- 



maxillary and transmits blood-vessels and nerves. MAXILLARY 



BONE, OB- 

 It articulates with the maxillary bone by this LIQUELY CRA- 



border 



The medial border is raised into a thin crest a , the three in- 

 of bone which, besides forming the medial wall of cis . or teeth . ; ^ 



palatal portion of 



the foramen incisivum or anterior palatine canal, the bone ; c, nasal 



articulates by its medial border with the bone of pro 



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 (r) 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. 



