346 LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



incision through the skin above the eye and deflect the skin downward toward the 

 eye on which you are working, stretching the skin away from the head.- On 

 the skin of the inner surface of the upper eyelid note a thin sheet of muscle fibers, 

 proceeding in a somewhat circular direction. This is orbicularis oculi, a part of 

 the platysma, and has the function of closing the eyelids. 



Rabbit: Stretch the upper eyelid away from the head and clean away the 

 connective tissue between it and the eyeball. A thin sheet of muscle will be 

 found extending from beneath the supraorbital arch to the upper eyelid. This 

 is the levator palpebrae superioris, which raises the eyelid. Repeat the foregoing 

 directions on the lower eyelid, stretching the skin away from the eyeball. On 

 the inner surface of the lower eyelid note the rest of the orbicularis oculi. The 

 depressor palpebrae inferioris may be noted extending from the zygomatic arch 

 to the lower eyelid; it lowers the eyelid. Remove the surrounding skin and 

 eyelids, cutting them away from the eyeball. With the bone clippers cut away 

 the supraorbital arch and clean away tissue between the dorsal surface of the 

 eyeball and the orbit. A slender but strong muscle will now be seen extending 

 from about the middle of the wall of the orbit to the dorsal surface of the eye- 

 ball; this is the superior oblique muscle. It separates the thin sheet of the 

 levator palpebrae superioris into two parts which pass on either side of it. Trace 

 the superior oblique to the wall of the orbit. Here there will be found a tendi- 

 nous cord, the trochlea, over which the muscle passes. Next, remove the levator 

 palpebrae superioris and find underneath its posterior portion the thin flat 

 superior rectus muscle. The insertion of the superior oblique on the eyeball is 

 concealed under the margin of the superior rectus. 



Remove the half of the mandible and the zygomatic arch on the side on 

 which you are working. This fully exposes the ventral side of the eyeball. 

 Along the ventral surface of the outer part of the eyeball extends the yellowish 

 infraorbital salivary gland. Medial to this extending beneath the eyeball is the 

 larger Harderian gland, which pours its secretion onto the nictitating membrane. 

 Remove these glands ; note the white part of the Harderian gland extending far 

 medially. The inferior oblique muscle is now seen extending to the eyeball 

 from the anteroventral region of the orbit. Posterior to it is the inferior rectus 

 muscle originating from the posteroventral region of the orbit. Note the branch 

 of the oculomotor nerve running along the anterior border of the inferior rectus 

 and supplying^both muscles. The nerve which runs along the posterior border 

 of the inferior rectus, innervating the lower eyelid, is the zygomatic branch of 

 the maxillary nerve. Immediately behind the inferior rectus is the external or 

 lateral rectus. The nerve passing along the posterior margin of the external 

 rectus is the lacrimal branch of the maxillary. It passes to the lacrimal gland 

 and to the skin between the eye and base of the pinna. The lacrimal gland is 

 a small reddish body which will be found by pressing the eyeball forward and 

 searching against the posterodorsal wall of the orbit. Two nerves pass the point 



