Bursalis muscle (Bm)
fibers, appearing as a derivative of the retractor bulbi muscle. It originates from fleshy, narrow fibers of the parabasisphenoid bone, spreading out to form an aponeurosis that inserts into the scleral cartilage. The origin site of the bursalis muscle is ventral to the optic nerve and posterior to the origin site of the retractor bulbi muscle. Its insertion site is ventral to the insertion site of the lateralis rectus muscle. The tendon of the bursalis muscle runs anterodorsally toward the upper eyelid and anteroventrally toward the lower eyelid\RL.
Origin: Fleshly, from the parabasisphenoid bone\RL.
Insertion: Aponeurotic, on the scleral cartilage\RL.
Function: Pulls the eyeball inward and outward within the socket.