Retractor bulbi muscle (Rbm)
The retractor bulbi muscle is a sheet-like muscle composed of parallel fibers that run ventrally to the ventralis rectus muscle. It originates from fleshy, narrow fibers of the parabasisphenoid bone, spreading out to form a broad aponeurosis that inserts on the scleral cartilage. The origin site of the retractor bulbi muscle is ventral to the optic nerve and anterior to the origin site of the bursalis muscle. Its insertion site is ventral to the insertion site of the ventralis rectus muscle on the scleral cartilage\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.