46 OSTEOLOGY OF THE HORSE. 



as well as most direct one: it extends along the inferior wall, from 

 the anterior to the posterior opening of the nose. 



The septum nasi is the partition separating one fossa from 

 the other. It is formed, posteriorly, by the ethmoidal plate ; in- 

 feriorly and posteriorly, by the vomer ; superiorly and anteriorly, 

 (and principally) by a broad perpendicular plate of cartilage. 



The openings of the nose are, — The anteinor, divided 

 by the nasal peak and septum nasi into two, and formed by the 

 superior borders of the anterior maxillary bones : the posterior, di- 

 vided after the same manner by the vomer and septum, and formed 

 by the nasal surfaces and crescentic borders of the palate bones. 



THE SINUSES OF THE HEAD communicate with, and 

 may be said to constitute part of, the nasal cavities. They are 

 the frontal, nasal, maxillary, sphenoidal, ethmoidal, and palatine. 



The frontal sinuses, formed within the frontal bones, are 

 situated so that a straight line extended between the supero- 

 internal angles of the orbits passes opposite to about the angular 

 or deepest parts of their cavities. The sinus (on either side) has 

 a triangular figure. The superior side or roof is flat, and (barring 

 the septa) even upon its surface ; whereas the posterior side 

 is irregular, being convex inwardly, where it is formed by the 

 cranial septum ; concave outwardly, where it is opposed to 

 the part composing the temporal fossa. The inferior side slants 

 from behind forwards, and from below upwards, is irregular 

 on its surface, and open or deficient outwardly, where the 

 cavity communicates with the maxillary sinus. Of the angles, one 

 is directed upwards; another downwards, terminating in the nasal 

 sinus, with which it is conjoined, the two forming one continuous 

 cavity ; the third points backwards, and is directly opposite to 

 the imaginary transverse line above alluded to. The cavity 

 is traversed and divided into several unequal open compartments 

 and recesses by septa ; the principal of which is one extended be- 

 tween the superior and inferior sides : it is partitioned from the 

 opposite sinus by the nasal spine. The sinus is but small in the 

 young compared to its proportionate dimensions in the adult sub- 

 ject : it continues to increase afterwards with age, and ultimately 

 extends throughout the whole of the frontal bone. 



The nasal sinuses, formed by the nasal bones above and 

 the superior turbinated bones behind, are nothing more than the 

 culs-de-sacs or blind terminations of the frontal sinuses. 



The maxillary sinuses, the largest of these cavities, arc 

 spacious but very irregularly formed. They are situated below 

 and in front of the frontal. Of this sinus, on either side, the 

 posterior and external walls are formed by the malar and lach- 



