The Muscular Arteries arise at the upper surface of the optic nerve; they are usually two in number: the inferior is a large and constant branch: after its origin it passes forwards between the optic nerve and the inferior rectus muscle: its branches are distributed to this muscle, to the inferior oblique and external rectus muscles, and to the lachrymal sac. The superior muscular artery is smaller and less constant: its branches are principally distributed to the levator palpebral, and to the superior and internal recti muscles; also to the superior oblique muscle, to the globe of the eye and the periosteum of the orbit. As we have already mentioned, the muscular arteries give off the anterior ciliary arteries.