254 
ANATOMY OF REGIONS. 
limit of the anterior and lateral faces of the head, on the line with 
' the separation of the cranium and the face, completed behind 
by a fibrous apparatus called the ocular sheath ; this last, which 
separates the ocular apparatus from the temporal fossa, belongs, 
also to the orbital cavity. 
The anterior opening of the orbits is turned outwards and 
slightly forward; its form is that of a circle, somewhat depressed 
sideways, and also a little from above below. Thus it resembles 
a rectangle, whose sides have been united by wide curves instead 
of sharp angles. The greatest dimension of the orbital opening 
extends from the orbital apophysis of the frontal to the zygoma¬ 
tic; it is consequently perpendicular to the palpebral fissure and 
about one-sixth longer than the transversal diameter The bones 
which form it are the larymal for the inferior anterior angle, 
the frontal for the internal and superior side, the zygomatic for 
the inferior and external. The extremity of the zygomatic pro¬ 
cess of the temporal, in reaching between the orbital portions of 
the frontal and the ascending process of the zygomatic, co-oper¬ 
ates to the formation of the external sides. 
The bony wall of the orbital cavity is complete only on the inter¬ 
nal side; outside its form is that of a wide ring,measuring between 
two and two and a half centimeters. It presents, at the supra- 
internal angle, the supraciliary foramen, which gives passage to 
an arteriol and to a division of the ophthalmic branch of Willis ; 
inside and above, a depression lodging the curve formed by the 
great oblique muscle, when reflecting itself upon the fibrous band 
which is attached on the border of that depression ; at last, in 
the infero-internal angle, a deep fossa ending by a canal, hollowed 
through the larymal bone and receiving the larymal sac, and 
the canal rising from it. 
The bony w r all of the superior face and the external side, is ex¬ 
tended posteriorly by the ocular sheath. 
This is a fibrous membrane, horn shaped, whose summit is at¬ 
tached to the edges of the orbital hyatus ; it is fixed forward up¬ 
on the bones already named, mingling with their periosteum. It 
is strong and thick in all the external part which has no bony 
base to rest on; on the internal side it is thinner and lays against 
