THE HORSE. 



97 



riorly : it is formed by the palatine por- 

 tions of the anterior and superior maxillary, 

 and by the palate bones. The surface is 

 transversely concave, and presents a slight 

 eminence a little behind its middle. 



Each lateral wall or side presents an 

 irregular concavity, and is formed by the 

 anterior and superior maxillary and the 

 palate bones. To it are attached the supe- 

 rior and inferior turbinated bones, by which 

 the fossa is divided into three separate pas- 

 sages or meatus. The superior meatus, 

 comprised between the' nasal and superior 

 turbinated bones, extends from the angle of 

 the lateral nasal opening, passing over the 

 ethmoidal cells, to the cribriform plate, fol- 

 lowing superiorly the declination of the 

 wall. The middle meatus, included between 

 the turbinated bones, leads superiorly into 

 the ethmoidal grooves and cells, and into 

 the sinuses of the head, and ends below, be- 

 neath the termination of the superior. This 

 passage, lUce the former one, is narrow ; but 

 its greatest diameter is, obUquely, in the 

 perpendicular direction ; whereas the other 

 measures most from side to side. It re- 

 ceives the apertures of the ductus ad 

 nasum, maxillary sinus, ethmoidal grooves, 

 and turbinated cells. The inferior meatus 

 is the most capacious as well as the 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 separat- 

 ing one fossa from the other. It is formed, 

 posteriorly, by the ethmoidal plate; infe- 

 riorly and posteriorly, by the vomer ; supe- 

 riorly and anteriorly, (and principally) by a 

 broad perpendicular plate of cartilage. 



The openings of the nose are : the ante- 

 rior, divided by the nasal peak and septum 

 nasi into two, and formed by the superior 

 borders of the anterior maxillary bones : 

 the posterior, divided 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, 



IS 



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 infe- 

 rior side slants from behind forward, and 

 from below upward, is irregular on its sur- 

 face, and open or deficient outwardly, 

 where the cavity communicates with the 

 maxillary sinus. Of the angles, one is 

 directed upward; another downward, ter- 

 minating in the nasal sinus, with which it 

 is conjoined, the two forming one continu- 

 ous cavity ; the thu-d points backward, and 

 is directly opposite to the imaginary trans- 

 verse 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 dimen- 

 sions in the adult subject: 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, are spacious but very irregu- 

 larly 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 lachrymal 

 bones, whose orbital processes constitute a 

 thin partition between it and the orbit ; the 



