146 OSTEOLOGY. 
optic foramen and forms the upper border of the sphenoidal fissure. Externally 
this surface is separated from the outer wall by the sphenoidal fissure posteriorly, 
anteriorly by an irregular suture between the orbital part of the frontal and 
the upper margin of the orbital surface of the great wing of the sphenoid, ex- 
ternal to which the external angular process of the frontal articulates with the 
malar. Internally the roof is marked off from the inner wall by a suture, more 
or less horizontal in direction, between the orbital plate of the frontal and the 
following bones in order from before backwards, viz. the frontal process of the 
superior maxilla, the lachrymal bone, and the os planum of ethmoid. In the 
suture between the last-mentioned bone and the frontal there are two foramina, 
the anterior and posterior internal orbital or ethmoidal canals (foramen ethmoidale 
anterius et posterius); both transmit ethmoidal vessels—the anterior affording 
passage to the nasal nerve as well. The roof is concave from side to side, and 
to some extent also from before backwards. About midway between the 
fronto-maxillary suture and the supraorbital notch or foramen, but within 
the margin of the orbit, there is a small depression, occasionally replaced by a 
spine (fovea vel. spina trochlearis), for the attachment of the cartilaginous pulley 
of the superior oblique muscle of the eyeball. Under cover of the external 
angular process the roof is more deeply excavated, forming a shallow fossa for the 
lodgement of the lachrymal gland (fossa glandule lachrymalis). In front, the roof 
separates the orbit from the frontal sinus, and along its inner border it is in relation 
with the ethmoidal air-cells. The relation to these air spaces is variable, depending 
on the development and size of the sinuses. The rest of the roof, which is very thin, 
forms by its upper surface the floor of the anterior cranial fossa,in which are lodged 
the frontal lobes of the cerebrum. 
The floor of the orbit is formed by the orbital plate of the superior maxilla, 
together with part of the orbital surface of the malar bone, and a small triangular 
piece of bone, the orbital process of the palate, which is wedged in posteriorly. 
Externally, for three- quarters of its length posteriorly, it 1s separated from the outer 
wall, which is here formed by the ereat wing of the sphenoid, by a cleft called the 
spheno-maxillary fissure (fissura orbitalis inferior), Through this there pass the 
superior maxillary division of the fifth nerve on its way to the infraorbital canal, the 
orbital or temporo-malar branch of the same nerve, the infraorbital vessels, and some 
twigs from Meckel’s (spheno-palatine) ganglion. By means of this fissure the orbit 
communicates with the spheno-maxillary fossa behind and the zygomatic fossa to 
the outer side. Internally the floor is limited from behind forwards by the suture 
between the following bones, viz. the orbital process of the palate below with the 
body of the sphenoid above and behind, and the os planum of the ethmoid above and 
in front—anterior to which the orbital plate of the superior maxilla below articulates 
with the os planum of the ethmoid and the lachrymal above and in front. At the 
anterior extremity of this line of sutures the inner edge of the orbital plate of the 
superior maxilla is notched and free between the point where it articulates with the 
lachrymal posteriorly and the part from which its frontal process rises. Here it 
forms the outer edge of a canal, down which the membranous nasal duct passes to 
the nose. The floor of the orbit is thin behind and at the sides, but thicker in 
front where it blends with the orbital margin. Passing in a sagittal direction 
through its substance is the infraorbital canal, the roof of which is usually deficient 
behind, where it becomes continuous with a broad, shallow groove, which leads 
forwards from the anterior margin of the spheno- maxillary fissure. This canal 
(canalis infraorbitalis) opens on the facial surface of the superior maxillary imme- 
diately below the orbital margin (foramen infraorbitale) and transmits the superior 
maxillary division of the fifth nerve, together with the infraorbital vessels. The 
floor forms a thin partition which separates the orbit from the antrum or sinus of 
the superior maxilla, which lies below. Internally it completes the lower ethmoidal 
air-cells, and separates the orbit from the middle meatus of the nasal fossz. 
The outer wall of the orbit, which is the strongest, is formed by the orbital 
surface of the great wing of the sphenoid and the upper part of the orbital surface 
of the malar bone. Above it, behind, is the sphenoidal fissure, whilst below, 
and extending much farther forward, is the spheno-maxillary fissure. The anterior 
