THE EYE. 183 



do not make any impression upon the eyes of man, and their eyes 

 are constructed accordingly. How extremely curious, for example, 

 are the 4,000 facets in the eyes of the common House-fly, 

 each one of which is a lens capable of forming a perfect image ; 

 and how strange to find that these are not sufficient, for there are 

 three ocelli in addition, each a single eye, and diff'erently placed in 

 the head ! And all of these are provided with those rods and 

 cones which are also found in our own eyes, and which seem to 

 render the optic nerve sensitive to rays of various vibrations. 

 How vast a field of enquiry and investigation still remains almost 

 unsearched, almost unknown, in the eyes of man, and of other 

 creatures ! 



If this paper will be in any degree an incentive to further 

 search, it will not have been written in vain. The space at our 

 disposal is too limited to go into the physiology of the eye at any 

 considerable length ; but such may form the subject of some 

 future paper. 



Owen's Comparative Anatomy, Riche's Physiology, and Gray's 

 Anatomy have been principally consulted in writing the above 

 paper. 



EXPLANATION OF PLATES XXXV. AND XXXVI. 



Fig. L — The Lachrymal Apparatus : — 



a, Lachrymal glands. b, Ducts, c, Puncta Laclirymata, 

 cl, Caruncula Lachrymalis. e, Canaliculi. /, Lachrymal sac. 

 g, Nasal Duct, h, Plica semilunaris. 

 The upper and lower eyelids are also shown. 



,, 2.— Muscles of the Eye :— 



ft, Levator palpedrse, upper. h, Superior oblique, c, 

 Superior Rectus. d, Pulley. e. Internal Rectus. /, 

 External Rectus, g, Inferior Rectus, h, Tarsal cartilage. 

 i, Upper Head of internal recti, k, Lower Head. /, Lesser 

 wing of Sphenoid, m. , Sclerotic. 



,, 3.— Vertical Section of Eyeball: — 



a, Sclerotic. h, Choroid, c. Retina, d, Hyaloid Mem 

 brane. e, Optic Nerve, f, Cornea, g, Anterior Chamber 

 of Iris. h, Posterior Chamber of same, i, Lens in its 

 Capsule. k, Ciliary processes. I, Cavity occupied by 

 vitreous humour, m. Tendon of Rectus, n, Ciliary Muscle 

 and Ligament. 0, Circular Sinus, p, Canal of Petit. 



,, 4. — Vertical Section of Cornea of Rabbit, hardened in chromic 

 acid : — a. Anterior layer of pavement of epithelium. b, 



