ORBIT. 
on the inner side a depression for the insertion 
of a pulley, through which rans the tendon of 
the superior oblique muscle. 
The inferior wall or floor is less extensive 
than the roof, and is directed upwards, out- 
wards, and forwards. It is formed chietly by 
the orbital plate of the superior maxillary bone, 
in front of this by the orbital process of the 
malar, and at the posterior part to a slight ex- 
tent by the orbital process of the palate bone. 
It presents a suture marking the union of the 
malar with the maxillary, and of the maxillary 
with the palate bone; about the middle of the 
floor is the infra-orbital groove, which passes 
forwards and becomes the infra-orbital canal. 
The external wall is directed inwards, for- 
wards, and slightly upwards; it is formed in 
_ front by the orbital process of the malar, and 
_ posteriorly by the orbital surface of the greater 
_ wing of the sphenoid. It presents a vertical 
_ suture at the junction of the malar with the 
sphenoid bone, and the orifices of some small 
eanals which open externally in the temporal 
fossa, and on the facial surface of the malar 
bone; some of these canals transmit filaments 
_of nerves from the lachryma!l branch of the 
ophthalmic, and from the superior maxillary 
herve. ' 
The internal wall is directed outwards, and 
‘slightly forwards and upwards: it is formed 
chiefly by the os planum of the ethmoid, in 
front of this by the lachrymal, and behind by 
‘the side of the body of the sphenoid. It pre- 
sents a vertical suture between the lachrymal 
‘bone and the ethmoid, and another between the 
latter bone and the sphenoid ; and anteriorly a 
vertical groove which lodges the lachrymal sac. 
_ Anetrs.—The superior and external angle 
formed by the junction of the superior with 
the external wall presents posteriorly the sphe- 
noidal fissure, sometimes called foramen lace- 
Tum anterius; in front of this a horizontal 
suture at the junction of the orbital plate of 
| the sphenoid with the orbital plate of the frontal 
| bone, and anterior to this the junction of the 
The superior and internal angle formed by 
e meeting of the superior and internal walls 
ents a suture between the os planum of 
the ethmoid and the orbital plate of the frontal ; 
in this suture are two small holes, the anterior 
i and posterior internal orbital holes ; the ante- 
b ior transmits the nasal branch of the ophthal- 
mic nerve, and the anterior ethmoidal artery ; 
the posterior gives passage to the posterior 
hmoidal artery; in front of the last-mentioned 
Suture is another between the lachrymal and 
frontal bones. 
The inferior and external angle, formed by 
the meeting of the inferior and external walls, 
esents posteriorly the spheno-maxillary fis- 
Sure, which is bounded externally by the orbital 
late of the sphenoid, internally by the orbital 
plates of the superior maxillary and palate 
bones, and in front usually by the orbital pro- 
cess of the malar bone, but occasionally by the 
Junction of the orbital plates of the superior 
maxillary and sphenoid bones at this point. 
The inferior and internal angle formed by 
4 
783 
the meeting of the inferior and internal walls 
presents a continuous horizontal suture, which 
in front connects the maxillary bone with the 
lachrymal, behind this the maxillary with the 
ethmoid, and still more posteriorly the palate 
bone with the ethmoid. 
The base or circumference is of an irregular 
quadrilateral form with curved sides and 
rounded angles; it inclines obliquely from 
within outwards. It is formed above by the 
supra-orbital arch of the frontal bone, on the 
outer side by the external angular process of 
the frontal and by part of the orbital border of 
the malar; below by the continuation of the 
orbital border of the malar, and by the corres- 
ponding orbital border of the superior maxillary 
bone; on the inner side it is completed by the 
nasal process of the superior maxillary, and the 
internal angular process of the frontal bone. At 
the junction of the middle with the inner third 
of the supra-orbital arch is the supra-orbital 
notch or foramen, which transmits the frontal 
nerve and vessels. There are three sutures in 
the margin of the orbit, one between the fron- 
tal and malar, a second between the frontal 
and superior maxillary, and a third between 
the malar and superior maxillary bones. At 
the junction of the lower with the inner border 
of the orbit is a small tubercle, the lachrymal 
tubercle, which is sometimes pointed out as a 
guide in the operation for fistula lachrymalis, 
but it is seldom very prominent even in the 
bare bone, and it could scarcely be detected 
through the tumefaction consequent on ob- 
struction of the lachrymal duct. The lachry- 
mal groove is immediately behind the internal 
margin of the orbit. 
In the apex of the orbit is the optic foramen 
situated between the two roots of the lesser 
wing of the sphenoid bone; the direction of 
the optic hole is backwards and inwards to- 
wards the centre of the sella Turcica. The in- 
ferior root of the lesser wing of the sphenoid, 
which separates the optic hole from the sphe- 
_noidal fissure, presents anteriorly a small tuber- 
cle which gives origin to the common tendon 
of the inteynal, external, and inferior recti 
muscles. 4 : 
Dissection of the orbit—Having removed 
the skull-cap and brain, the roof of the orbit 
may be taken away by two vertical cuts with 
a saw, the inner cut extending from a point 
just external to the internal angular process, 
backwards along the roof to the optic foramen, 
the outer cut extending from a point just in- 
ternal to the external angular process, also back- 
wards to the optic foramen. In making these 
cuts care must be taken to avoid injuring in 
front on the inner side the pulley and tendon 
of the superior oblique muscle, on the outer 
side the lachrymal gland with its vessels and 
nerves, and posteriorly the optic nerve and 
ophthalmic artery passing through the optic 
hole. Having removed the bony part of the 
roof the periosteum is exposed, and must be 
examined before proceeding farther. 
The periosteum of the orbit appears to be a 
continuation of the dura mater; it passes in 
through the optic hole, and through the sphe- 
