THE SKULL. 45 



presphenoid, and each half of it is produced caudad near the 

 middle line into a triangular spine which lies ventrad of the 

 body of the presphenoid. The horizontal portion of the bone 

 helps to separate the olfactory and respiratory passages of the 

 nasal chamber, while its vertical portion contributes to the 

 formation of the nasal septum. 



The ventral margin formed by the junction of the two 

 halves of the bone is smooth and free caudad, but at its cranial 

 end is broad and rough for articulation with the palatal 

 processes of the maxillae. 



Palatine Bone. Os palatinum '(Fig. 33). The palate 

 bone or palatine bone consists of two portions, a horizontal or 

 palatal portion (a) and a perpendicular or nasal portion (6), 

 uniting at an angle of about forty-five degrees. 



The horizontal portions (a) of the two bones are received 

 between the maxillary bones and form the caudal and medial 

 part of the roof of the mouth. Each is irregularly 

 quadrilateral in form, with the caudolateral angle 

 produced caudad into a long process which is 

 continuous with the perpendicular portion of the 

 bone. The lateral margin of the horizontal por- 

 tion articulates over its cranial half with the 

 maxillary bone. At about its middle a short thick 

 maxillary spine (c) projects caudolaterad. The FIG. 33. PALA- 

 remainder of the lateral margin is directly con- DORSAL VIEW' 

 tinuous with the perpendicular plate of the bone. a , horizontal 



The medial margin is rough for articulation with P ort '? n : ^ P er - 



pendicular por- 



the corresponding margin of the opposite pala- tion; r, maxillary 

 tine ; the caudal angle of this margin projects ^ *ffJ 

 caudad as the short posterior nasal spine (d}. sphenopaiatine 



T-I 11 r f j 1-1 foramen; _/. cau 



Ihe caudal margin forms a free edge which ^ai opening of 



bounds the choanos ; it passes laterally into the posterior palatine 



canal. 



perpendicular portion. 



The ventral surface (Fig. 41, 8) looks into the mouth. 

 Near the middle of its craniolateral margin are two or more 

 small foramina (Fig. 41, q] which form the cranial temination 

 of the posterior palatine canal. The dorsal surface is smooth 

 and looks into the nasal cavity. 



