92 



ANATOMY OF THE RABBIT 



Vibrations of the ear drum are transferred to a chain of ossicles 

 in the middle ear (Figs. 47 and 90) the innermost of which fits 

 loosely into an opening in the wall of the bony labyrinth and thus 

 passes on the vibrations as pressure changes to the perilymph, 

 which in turn transmits them to the organ of Corti. 



The Eye 



The eye is the special organ for the reception of stimulation by 

 light and consists of a specialized portion of the brain, the retina, 

 which has grown out on the end of a stalk of nervous tissue to come 

 close to the surface and has been provided with a mechanism for 

 focussing light rays upon it, the whole being enclosed in a support- 

 ing and protective capsule. The capsule is nearly spherical and is 

 composed of exceedingly dense connective tissue which forms an 

 opaque white coat, the sclera, 

 except over the exposed outer 

 surface of the eye. 



On the exposed surface of 

 the eye, the sclera is suddenly 

 replaced by a transparent 

 sheet of modified connective 

 tissue which is fused with a 

 thin outer layer corresponding 

 with the epithelium of the con- 

 j unctiva (the lining layer on the 

 inner surface of the eyelids). 

 This outer layer of the eye is 

 also perfectly transparent and 

 along with the transparent 

 connective tissue constitutes the cornea, a highly refractive curved 

 window. Internally, separated from the cornea by chambers con- 

 taining a fluid, the aqueous humour, is suspended the lens, which 

 is biconvex, somewhat more curved on its inner than on its outer 

 surface, and composed of modified epithelium. This is suspended 

 in a very thin capsule by a ring of fibres, the zonula ciliaris, which 

 fibres are attached at their outer ends to a circular ridge of muscle, 

 the ciliary body. The zonular fibres are under tension when the 

 muscle is at rest, keeping the lens slightly flattened, and when the 



Fig. 48. Diagram of the parts of the eye in 

 vertical section: c.a., anterior chamber; c.c, 

 ciliary body; ch., chorioidea; co., cornea; c.p., 

 posterior chamber; c.r., ciliary portion of the 

 retina; c.v., vitreous body; d.h., Harderian duct; 

 d.l., position of the lacrimal ducts; d.n., nasola- 

 crimal duct; i., iris; 1., lens; n.o., optic nerve; 

 o.r., optic portion of the retina; p.i., lower eye- 

 lid; p.s., upper eyelid; p.t., third eyelid; r.b., 

 retractor oculi; r.i., rectus inferior; r.s., rectus 

 superior; sc, sclera; z., suspensory zonular 

 fibres of the lens. 



