ANATOMY OF THE HORSE. 
347 
II. — THE ORBITS, 
Two in number, are formed for the lodgement, attachment, 
and protection of the eyes and their appendages. 
Figure. —Symmetrical. The cavity, which is extended hori¬ 
zontally backward and inward, has, viewed in front, a pyramidal 
aspect: the base, represented by the front, has four sides and 
four angles; one only of the sides, however, is sufficient in extent 
to reach the apex, the others being all more or less imperfect. 
A line drawn in the horizontal direction through the axis of this 
figure, inclines more outwards than forwards, more fonvards than 
downwards, intersecting another horizontal line projected directly 
forward at an angle of about 70^, and one extended laterally, di¬ 
rectly outward, (at right angles with the former) at about 20^: 
the inclination downward, however, will in course vary with the 
erect position of the head. 
Structure. —The orbit is composed of unequal portions coming 
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 con¬ 
sists only of the frontal arch; which is concave and smooth inter¬ 
nally, to make room for the lachrymal gland, and has anterior 
and posterior borders, 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 straighter 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 
hones, 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 the transverse suture with the lachrymal bone. Its 
border in front, though slightly curvated, is very irregular, 
having several notches and one or two small foramina 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 tempora contributing but little: it is concave and smooth 
