OSTEOLOGY OF THE HORSE. 45 



THE APEX or back of the orbit, formed by the ctlimoid, 

 sphenoid, and palate bones, is pierced by five foramina: the two 

 round are tlie internal orbital and optic, which are ranged in a row 

 with two oval and larger in size, t/ie supero-posterior and infero- 

 posterior orbital ; the one behind is t/ie spinal foramen. 



III. CAVITIES OF THE NOSE, 



Comprehending the nasal fossse or chambers, and the sinuses. 

 These cavities occupy about two-thirds of the internal space of 

 the superior maxilla, the remaining third belonging to the cranium ; 

 from which they are partitioned by the cranial septum of the 

 frontal bone, in union with the cribriform plates and crest of the 

 ethmoid. 



THE NASAL FOSS^ may be said to include about two- 

 thirds of the entire space devoted to the olfactory cavities. They 

 constitute the interior of the proboscis; have four boundary walls, 

 one above, one below, and two laterally ; are separated from each 

 other by a septum ; but are open both before and behind. 



The SUPERIOR wall presents an irregular concave formed by 

 the internal surfaces of the nasal bones, the cells and grooves of 

 the ethmoid, and small portions of the nasal surfaces of the palate 

 bones. 



The INFERIOR WALL is horizontal; it extends forwards be- 

 yond the superior, but is considerably overreached by that wall 

 posteriorly : it is formed by the palatine portions 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 wALLor side presents an irregular concavity, 

 and is formed by the anterior and superior maxillary and the palate 

 bones. To it are attached the superior and inferior turbinated 

 bones, by which the fossa is divided into three separate passages 

 or meatus. T/ie 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, following superiorly the declination of the wall. The mid- 

 dle meatus, included between the turbinated bones, leads superi- 

 orly into the ethmoidal grooves and cells, and into the sinuses of 

 the head, and ends below beneath the termination of the superior. 

 This passage, like the former one, is narrow ; but its greatest 

 diameter is, obliquely, in the perpendicular direction ; whereas 

 the other measures most from side to side. It receives the aper- 

 tures of the ductus ad nasum, maxillary sinus, ethmoidal grooves, 

 and turbinated cells. The inferior meatus is the most capacious 



