(2.46)

The seven muscles in the orbit that these nerves supply are the four rectus muscles, the two oblique muscles, and the levator of the upper lid. The oculomotor nerve supplies five muscles, the trochlear and abducent nerves supply just one muscle each.

To follow these nerves we'll move forward to the orbit again. We'll divide and displace the two muscles in the roof of the orbit. These are the levator of the upper eyelid, levator palpebrae superioris, and beneath it, the superior rectus muscle.

Here's the optic nerve, as we've seen already. Here's the superior oblique muscle, going round its pulley or trochlea. Here are the medial rectus, and lateral rectus muscles.

We'll go round to a front view to see the nerves better. The oculomotor nerve divides into an upper and lower branch.

Here's the upper branch, supplying the levator palpebrae superioris and superior rectus muscles. To see the lower branch we'll remove the optic nerve. Here again are the medial and lateral rectus muscles, down here is the inferior rectus.

The only muscle not on view here is the inferior oblique, which is beneath the eyeball here. Here's the lower branch of the oculomotor nerve. It supplies the medial rectus and inferior rectus, and the inferior oblique muscles.

In addition, through these short ciliary nerves, the oculomotor nerve contributes to the autonomic supply to the intra-ocular muscles, that control the size of the pupil, and the shape of the lens.

Here's the trochlear nerve, the fourth cranial nerve. It supplies just the superior oblique muscle. Here's the abducent nerve, the sixth, supplying its one muscle, the lateral rectus, which abducts the eye.

We'll be returning to the orbit once again in just a minute, to look at branches of the fifth nerve, the trigeminal. For now we'll replace the contents of the orbit, including this nerve, the frontal nerve, which is part of what we'll come to next.