THE HEAD. 



from side to side and almost smooth. The 

 posterior, internal, or nasal face exhibits a ver- 

 tical crest passing along the external border 

 of the bone, which gives attachment to the 

 nated portion of the ethmoid; at its supe- 

 rior extremity this crest bifurcates, and between 

 its two branches shows a concave surface which 

 forms part of the frontal sinus. For the 

 remainder of its extent the internal face is 

 smooth, and covered by the mucous membrane 

 of the nasal fossa ; it is also excavated into a 

 channel to form the superior meatus of this 

 cavity. 



Borders. The external border is very thin 

 in its upper two-thirds, and articulates with 

 the lachrymal bone, the anterior border of 

 the supermaxillary, and the upper extremity 

 of the premaxillary bones. In its lower third 

 it becomes isolated from the latter bone, in 

 forming with the anterior border of its large 

 process a very acute re-entering angle whose 

 opening looks downwards. The internal border 

 is denticulated to correspond with the opposite 

 bone. 



Base and Summit. The base occupies the 

 superior extremity of the bone; it describes 

 a curved line with the convexity above, and in 

 uniting on the median line with that of the 

 opposite bone, forms a notch similar to that 

 of the heart figured on playing cards; it is 

 bevelled at the expense of the internal plate to 

 articulate with the frontal bone. The summit 

 of the two nasal bones, which is pointed, 

 constitutes the nasal prolongation: the name 

 given to a single triangular process which 

 comprises all that portion of the nasal bones 

 separated from the premaxillaries by the re- 

 entering angle before mentioned. 



Structure and development. Almost entirely 

 compact in structure, it is developed from a 

 single centre. 



8. Turbinated Bones. 



The turbinated bones, two on each side, 

 represent two irregular bony columns, wider 

 above than below, compressed laterally, hol- 

 lowed internally, and lying vertically side by 

 side on the external wall of the nasal fossa, 

 which they divide into three meatuses or pas- 

 sages. 



They are distinguished into anterior and 

 posterior turbinated bones. 



The anterior or superior, also named the 



Fig. 22. 



ANTERO-POSTERIOR AND VERTICAL 

 SECTION OF THE HORSE'S HEAD. 



1, Condyloid foramen ; 2, Parietal 

 protuberance ; 3, Internal audi-- 

 tory hiatus ; 4, Cerebral cavity ; 

 5, Cerebellar cavity ; 6, Supe- 

 rior border of the perpendicular 

 plate of the ethmoid bone (crista- 

 galli process) ; 7, Ethmoidal 

 volutes nasal face ; 8, Vestiges 

 of the right frontal sinus -, 9, 

 Ditto of the sphenoidal sinus ; 

 10, Pterygoid process; 11, Eth- 

 moidal turbinated bone; 12, 

 Maxillary turbinated bone; 13, 

 Crest of the supermaxillary 

 bone to which the latter is fixed ; 

 14, Vomer. A, Orifice of com- 

 munication between the nasal 

 cavity and the sinus. 



