• ANATOMY OF THE HORSE. 
147 
the frontal arch and articulating with the temporal bone: un¬ 
derneath, the arch is excavated for the reception of the lachry¬ 
mal gland ; and through its inward end is a hole, (in some rare 
instances, two,) the supra-orbital foramen, for the transmission 
of a small artery and nerve of the same name to the forehead ; 
below the foramen, internally, is a small depression, marking the 
place of attachment of the cartilaginous pulley belonging to the 
superior oblique muscle of the eye. From below and behind 
the arch proceeds downwards and backwards the inte'rnal orbi¬ 
tal process or plate, divided into two by a notch into which pro¬ 
jects the wing of the ethmoid bone, whose extremity is inclosed 
in a mortise formed in the base of this plate; this part also 
articulates, within the orbit, inferiorly, with the sphenoid, pos¬ 
teriorly with the temporal, and anteriorly with the lachrymal 
and superior maxillary bones. The anterior portion of this pro¬ 
cess, behind, where it joins the sphenoid, is pierced by the in¬ 
ternal orbital foramen, which gives passage to the lateral nasal 
nerve ; the surface behind the posterior portion is smooth and 
depressed, making by union with it part of the temporal fossa. 
The Internal Surface is divided by a vaulted cranial septum 
into two unequal concavities : the posterior forms a cap for the 
anterior lobe of the cerebrum, which rests upon the septum, the 
indentations upon the surface answering to the cerebral emi¬ 
nences ; the anterior concavity forms the frontal sinus, whose 
interior is much enlarged by the slant taken by the septum, and 
the cavity continues to extend with age until it occupies the en¬ 
tire front of the bone. One frontal sinus is separated from the 
other by the nasal spine, composed of a lamina from each 
bone; there are also several imperfect septa traversing the inte¬ 
rior of each sinus, partially dividing it into so many different 
chambers. 
Borders, Denticulated and squamous. The posterior or pa¬ 
rietal is arched, describing segments of two distinct circles, one 
running from within outwards, the other from above downwards, 
and these are overlaid by the parietal and temporal bones. The 
anterior or nasal border is waving, inclines backwards as well 
as outwards, is terminated internally by the nasal process, and 
is overlapped by the nasal and lachrymal bones. The frontal 
border is straight; broad and triangular anteriorly, where it 
forms the septum between the sinuses : it unites with its fellow; 
and has at the place of junction, internally, a slightly elevated 
longitudinal crest or spine, which with the opposite one forms a 
groove for the reception of the longitudinal process of the dura 
mater. The ethmoidal or outer border is irregular, forming a 
