ORBIT. ( Orbis, any thing round : Fr. bite; Germ. Augenhiihle.)—In the present artil it is intended to describe, first, the bony frani work of the orbit; secondly, the contents* of orbit in the order in which they are exposed I a dissection from the roof to the floor of the cavil and, lastly, to give some account of the actI of the nausdes contained in the orbit and I serted into the upper lid and globe of the eyi The orbits are two in number, situated at anterior and upper part of the face. Tll have the form of quadrangular pyramids, bases of which are directed forwards and o wards, the apices backwards and lima Each orbit-presents for examination four wa four angles, formed by the meeting of the wa a base, and an apex.
The superior wall or roof is concave and rected downwards and slightly forwards. I chiefly formed by the orbital plate of the fr bone; at the posterior part to a slight ex the lesser wing of the sphenoid. It the suture between the orbital plate frontal and the lesser wing of the spheno anteriorly on the outer side the la fossa, which receives a gland Of the same on the inner side a depression for the insertion of a pulley, through which runs 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 chiefly by the orbital plate of the superior maxillary bone, in front of tills 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 rnalar with the sphenoid bone, and the orifices of some small canals 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 lachrymal branch of the ophthalmic, and from the superior maxillary nerve. .
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.
ANoLvs.—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 rum 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 malar with the frontal bone.
The superior and internal angle formed by the meeting of the superior and internal walls presents 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 and posterior internal orbital holes ; the ante rior transmits the nasal branch of the ophthal mic nerve, and the anterior ethmoidal artery ; the posterior gives passage to the posterior iethmoidal artery; in ftont of the last-mentioned !suture is another between the lachrymal and ifrontal bones.
1 The inferior and external angle, formed by , the meeting of the inferior and external walls, presents posteriorly the spheno-maxillary fis . sure, which is bounded externally by the orbital plate of the sphenoid, internally by the orbital Iplates of the superior ma-xillary and palate Pones, and in front usually by the orbital pro 'cess of the rhalar bone, but occasionally by the unction of the orbital plates of the superior axillary and sphenoid bones at this point.