This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
The orbit is lined with a periosteum, and contains the eyeball, the muscles which move it, the veins, arteries, and nerves which go to it together with some which traverse the orbit to go to the face, and the lachrymal gland. These structures are more or less surrounded with a fascia which is continuous with the periosteum.
Fig. 88. - Sagittal section through the eye and orbit.
The periosteum of the orbit is not tightly attached and in cases of disease can readily be raised from the bone beneath. Anteriorly, it is continuous at the orbital rim with the periosteum of the bones of the face. Posteriorly, it is continuous through the optic foramen and sphenoidal fissure with the dura mater. It sends prolongations inward, covering all the separate structures in the orbit. From the edge of the orbit it stretches over to the tarsal cartilages, forming the superior and inferior orbilotarsal ligaments. These form a barrier (called the sep-. turn orbitale) to the exit of pus from within the orbit, and for that reason it is advised that orbital abscesses should be opened early. The lower portion, as it reaches the lachrymal groove, splits to cover the lachrymal sac. Another extension from above splits to enclose the lachrymal gland, which is seen to lie comparatively loose in the upper outer portion of the orbit, sustained by its suspensory ligament. It then sends thin fibrous layers which cover the muscles, arteries, veins, nerves, fat pellicles, and finally the eyeball posterior to the insertion of the muscles and optic nerve. This last portion, called the capsule of Tenon, begins as far forward as the insertion of the recti muscles on their under (inner) side, passes over the globe posteriorly, over the optic nerve, and blends with the layer covering the deep surface of the muscles. It is joined to the sclerotic coat of the eye and dural sheath of the nerve by a loose net-work of delicate fibrils. This forms practically a space lined with endothelial plates, similar to the subarachnoid space in the brain. The capsule of Tenon is a distinct, well marked membrane, and the eyeball lies loose and revolves freely within it. It is this space into which the strabismus hook is put when it is desired to cut the recti muscles for squint. Fibrous prolongations are also sent to the sides of the orbit from the internal and external recti muscles. They are the check ligaments; and one from the inferior rectus forms the suspensory ligament of the eye.
The orbit is often invaded by tumors, pus, hemorrhages, and air (producing emphysema).
Tumors may either originate in the orbital contents, as sarcomas of the lachrymal gland or eye, or they may come from surrounding regions. It is more rare for them to enter through the natural openings of the orbit than it is for them to push through its thin walls. Coming through natural openings, they may make their entrance: (I) from the brain through the optic foramen or sphenoidal fissure;
(2) from the region of the zygomatic and temporal fossae through the sphenomaxillary fissure; (3) from the nasal cavities (as I have seen), coming up the lachry-monasal canal.
In invading the orbit through its walls they may come: (1) from the nasal cavities and ethmoidal cells, pushing through the thin internal wall; (2) from the frontal sinus, appearing at the upper innerangle;
(3) from the sphenoidal cells at the posterior portion of the inner wall; (4) from the brain cavity above, breaking through the roof; (5) from the maxillary sinus below, pushing through the floor.