11 OSTEOLOGY OF THE HORSE. 



from four of the bones of the cranium, and from three of those of 

 the face : viz. the frontal, ethmoid, sphenoid, and temporal 

 bones; the malar, lachrymal, and palate bones. 



Division. — Into sides, angles, base, and apex. 



SIDES. — The superior side or roof of the cavity consists 

 only of t/te frontal arch; which is concave and smooth internally, 

 to make room for the lachrymal gland, and has anterior and pos- 

 terior borders, sharp and slightly curvated. The inferior side 

 or floor of the orbit is formed by the orbital surfaces of the lach- 

 rymal and malar bones, is broader than the roof, though, like it, 

 is deficient as a whole. It comprises the orbital portion of the 

 lachrymal suture: it is terminated, in front, by a smooth, 

 rounded, curvated border ; behind, nearly midway between the 

 base and apex, by a shorter and straight er border. The inter- 

 nal or NASAL SIDE, the broadest and only complete one, is 

 formed principally by the internal orbital process of the frontal 

 bone, into the notch of which is received the os planum : the 

 ethmoid bone further contributes, and also the sphenoid and palate 

 bones, the three constituting that irregular termination of the ca- 

 vity behind which represents the apex. The frontal orbital plate 

 is smooth and slightly concave, and is united below by a conti- 

 nuation of tJie transverse suture with the lachrymal bone. Its 

 border in front, though slightly curvated, is veri/ irregular, 

 having several notches and one or tivo smallforamina in it; it also 

 presents a little tubercle, to which the lachrymal caruncle is 

 attached. The external or zygomatic side is formed 

 principally by the zygomatic process of the malar bone, that of 

 the temporal contributing but little : it is concave and smooth 

 internally, somewhat broader below than upwards ; is intersected 

 obliquely by the zygomatic suture, and has an anterior border, 

 smooth and curvated ; a posterior one, sharp and straight. 



ANGLES. — The supero-internal angles, one before, 

 the other behind, are formed by the beginning of the frontal arch, 

 through which, midway between them, passes the supra-orbital 

 foramen. The infero-internal angle includes the lachrymal fossa. 

 The sijpero-externa l angles, one anterior, the other pos- 

 terior, are intersected by the suture uniting the frontal and zy- 

 gomatic arches. The infero-external angles, particularly the an- 

 terior, are rounded and smooth. 



BASE. — Of the circumferent border, the superior and internal 

 parts, about two-fifths of the entire circle, are formed by the 

 OS frontis ; the inferior and internal parts, about one-fifth, by the. 

 lachrymal bone ; and the remaining two-fifths by the malar and 

 temporal bones, in the proportion of three parts of the former to 

 one of the latter. 



