In the images below, you are looking at the left orbit and the medial side of the orbit is to the left.

Bones frontal zygomatic maxilla lacrimal ethmoid greater & lesser wing of sphenoid palatine

Orbital foramina optic superior orbital fissure inferior orbital fissure posterior ethmoid anterior ethmoid

Structures that pass through the foramina are:

• optic nerve and ophthalmic artery through the optic foramen
• oculomotor, trochlear, V1 and abducens through the superior orbital fissure
• anterior & posterior ethmoid nerves through the anterior & posterior ethmoid foramina
• infraorbital nerve through the inferior orbital fissure

The rest of the orbital cavity is filled with orbital fat, muscles of the eyeball, the eyeball, the lacrimal gland, ophthalmic artery and its branches, and the ophthalmic vein and its tributaries. We will start examining the contents of the orbit from above down.

When the frontal bone is chipped away and the orbit is entered, the first thing you will see is a connective tissue structure enclosing the eyeball and its muscles, vessels and nerves, the periorbita. This is a glistening structure.
After the periorbita is stripped away, you will then encounter a large amount of fat filling the structures in the orbit. Once this fat is cleaned away, you will find the following structures: trochlear nerve (T) frontal nerve (F) supraorbital nerve (SO) supra trochlear nerve (ST) lacrimal nerve (L) lacrimal gland (Lac) levator palpebrae superioris (LPS) After these structures are identified, the levator palpebrae superioris is reflected forward and the next layer of items is revealed.
In this layer, we see three muscles: superior oblique (SO) superior rectus (SR) lateral rectus (LR) and the nasociliary nerve (nc) anterior ethmoid (ae) posterior ethmoid (pe)
Finally, we reach the orbital floor which is made up of the zygomatic and maxillary bones. A sulcus can be seen in the maxillary bone and this holds the infraorbital nerve (ION). The zygomatic bone has a zygomatic foramen which accepts the zygomatic branch of the infraorbital nerve (Z). The infraorbital nerve is a branch of the maxillary division (V2) of the trigeminal nerve. It enters the orbit through the inferior orbital fissure.

Once the structures in the orbit are learned, you should then try to understand how the muscles act on the eye to move it. This knowledge is necessary in clinical situations when you examine the eye during a full physical examination or after head injuries. In order to fully understand the movements of the eyeball you should realize that the eyeball moves around three axes: (1) vertical, (2) horizontal and (3) anteroposterior. Movements around the vertical axis are abduction and adduction, around the horizontal axis, elevation and depression and around the anteroposterior axis, medial and lateral rotation. This last movement usually requires the use of special equipment to see it, so we won't consider it at this time.

In the adjacent figures, we point out the muscles that perform the various movements of the eye (The 3 axes are in black): Elevation is movement of the eye around the horizontal axis so that it is looking upward. This movement is performed by a pair of muscles: superior rectus (SR) inferior oblique (IO) Depression is movement of the eye around the horizontal axis so that it is looking downward. This movement if performed by a pair of muscles: inferior rectus (IR) superior oblique (SO)

adduction is movement of the eye around the vertical axis so that it is looking toward the nose. There is only one muscle that originates this movement. medial rectus (MR) abduction is movement of the eye around the vertical axis so that it is looking laterally. The muscles that perform this action are: lateral rectus (LR) superior oblique (SO) inferior oblique (IO) superior rectus (SR) inferior rectus (IR)

The only artery supplying structures in the orbit is the ophthalmic artery which is a branch of the internal carotid just before that artery enters into the formation of the Circle of Willis. It enters the orbit with the Optic nerve through the optic foramen. It gives rise to the very important branch, the central artery of the retina.