408 Harris Ha^vtho^ne Wilder 



Certain peculiarities of the nerves demand attention. The two 

 Motores oculi, coming from the two brains, become continuous with one 

 another and form a common trunk stretched transversely across the 

 middle line back of the eyeball. From this small twigs arise and supply 

 the muscles, and a similar one, lateral to the others, forms a communicat- 

 ing branch with the Abducens of each side. The two ophthalmic 

 branches of the Fifth nerve, having no chance to reach the exterior, 

 ramify the inner surface of the frontal bone ; but a small median nerve, 

 the connection of which I was unable to find (Fig. 25 b), passes between 

 the two vestigial tarsal cartilages and is probably distributed to the pro- 

 boscis, and possibly also to the infolded skin lining the palpebral canal 

 next to be described. This branch is probably derived from the ophthal- 

 mic nerve, although this was not proven. 



The eyeball, which was situated far in the interior of the head, was 

 attached to the center of a blind front wall by means of a membraneous 

 stalk that proved upon examination to be hollow and to constitute a part 

 of the wall of a canal that ran forwards in the middle line and came to 

 the exterior immediately beneath the base of the proboscis. The laying 

 open of this canal proved its nature, for its walls contained all of the 

 antorbital structures, even including a small portion of the face. Beyond 

 the membraneous tube, which undoubtedly represents the conjunctiva, 

 lies a pair of carunculse lacrimales, followed by a double ridge composed 

 of Meibomian glands, and just beyond these a well defined row of eye- 

 lash rudiments. This region, still within the canal, is followed by nor- 

 mal integument, furnished with delicate hairs. Outside of this canal, 

 at about the outer limit of the conjunctival membrane and placed dorso- 

 laterally, is a pair of minute nodules of cartilage, each somewhat in the 

 form of a capital D, and into these are inserted the pair of muscles 

 identified above as the levator palpebral; farther down on the sides 

 of the canal is a pair of large glandular masses. These structures are 

 plainly the tarsal cartilages and the lacrimal glands, and from these and 

 the other features we can see that the entire canal is formed by a turning 

 in of the normal external parts accessory to the eyeball. The matter 

 becomes at once clear if one imagines a normal pair of eyeballs first 

 fused into a single symmetrical one and then drawn back into the 

 interior of the head, taking with it the parts that are attached to it. 

 The conjunctiva, turned wrong side out, save the part covering the front 

 of the eyeball itself, would form the innermost part of the canal, then 

 would come the margins of the lids, and lastly the external skin in the 



