MUSCLES OF EYEBALL. 65 
runs downwards and slightly backwards to be 
inserted into the outer surface of the mandible, 
just in front of the joint. 
To see the insertions of these last three muscles the mouth should 
be opened widely. 
3. Muscles of the eyeball. 
Remove the temporal and pterygoid muscles carefully, dissecting 
them away from their origins, and then turning the muscles down 
and cutting them short close to their wsertions. Remove also the 
lower jaw: pin the frog out on its back and dissect away carefully 
the mucous membrane of the roof of the mouth : note 
i. The levator bulbi: a thin sheet of muscle lying 
* between the mucous membrane and the eye. Its 
fibres arise from the side of the skull, run out- 
wards underneath the eye and are inserted into 
the upper jaw. The muscle by its contraction 
serves to lift up the eyeball and so make it more 
prominent. Some of its fibres are inserted into 
the lower eyelid which they serve to depress, 
acting as a depressor palpebre inferioris. 
Remove the levator bulbi and clean the remaining muscles, 
dissecting them partly from the dorsal and partly from the 
ventral surface. 
a. The recti muscles: a group of four small muscles which 
arise close together from the inner and posterior angle 
of the orbit close to the optic foramen, and run 
forwards and outwards, diverging from one another, to 
be inserted into the bulb of the eye. 
i. The rectus superior: inserted into the dorsal sur- 
face of the eyeball: seen best from above. 
ii. The rectus externus: the most posterior of the 
four: inserted into the posterior surface of the 
eyeball: seen best from the side or from below. 
iii. The rectus internus: the longest of the four: runs 
forward between the skull wall and the eyeball, 
and is inserted into the inner or median surface 
of the eyeball: seen best from below. 
L- 
