348 
ANATOMY OF THE HORSE. 
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 supero-external 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 foniied 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. 
THE APEX or back of the orbit, formed by the ethmoid, 
sphenoid, and palate bones, is pierced by five foramina; the two 
round are the internal orbital and optic j which are ranged in a row 
with two oval and larger in size, the supero-posterior and infero- 
posterior orbital: the one behind is the 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 NASx4L FOSSriE may be said tto include about two- 
thirds of the entire space devoted to the olfactory cavities. They 
constitute the interior of the proboscis ; have four boundaiy 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 maxillaiy, and by the palate bones. The surface is 
transversely concave, and presents a slight eminence a little behind 
its middle. 
