186 
ANATOMY OF THE HORSE. 
maxillary nerve. Immediately over the hiatus is the opening 
of the canal which conducts the pathetic nerve into the orbit : 
it is in part formed by the ethmoid bone. 
The Superior or Cerebral Surface is unevenly concave, being 
impressed by the middle lobes of the cerebrum, which it sup¬ 
ports. It presents three general concavities :—a middle and 
two lateral. In the centre of the middle division is tl^e pitua- 
tury fossa for lodging the gland from which it takes its name ; 
it is bounded on the sides by the optic fossae, which are occu¬ 
pied, inwardly, by the optic nerves, outwardly, by the cavernous 
sinuses. Farther removed outward and forward is the foramen 
lacerum orbitale, and immediately over it the spinal foramen, 
through which passes the pathetic nerve before it enters its 
canal. 
Borders. The Posterior or Occipital consists of an oval solid 
part in the middle, which is united with the basilar process of 
the occipital bone, and, laterally, of two wide irregular notches 
contributing to the formation of the foramina lacera basis cranii. 
—The Anterior or Palatine Border has a similar oval middle, 
joined to the ethmoid bone; and has a connection also with the 
vomer.—Each Lateral Border is distinguishable into two parts : 
—a posterior, which is scaly and denticulated for adaptation to 
the squamous temporal bone; and an anterior or orbital por¬ 
tion, projected forward to unite with the anterior extremity of 
the same bone, and also with the ethmoid, while it forms the 
posteriormost part of the orbit. 
Connection —With the occipital, ethmoid, and squamous tem¬ 
poral bones; also with the palate bones and vomer. 
ETHMOID BONE. (OS ETHMOIDES.) 
Situation, Antero-inferior part of the cranium; immediately 
before the sphenoid bone ; where it constitutes the partition be¬ 
tween the cranial and nasal cavities. 
Form, One portion, the posterior, bears a resemblance to a 
bird with its wings extended, as in the act of flight, having no 
legs, but a long erected neck and a small round head ; the an¬ 
terior part consists of a thin, brittle, porous, spongy structure, 
of considerable volume. 
Division —Into a middle and two lateral parts. 
The Middle Portion is large in bulk, consisting of a body be¬ 
hind, and of two voluminous spheroid spongy masses in front 
parted by a septum. The body is oblong from before back¬ 
wards, concave superiorly, convex inferiorly, and interiorly 
formed into two concavities, the ethmoidal sinuses; these are 
