370 ANATOMY IN A NUTSHELL. 



There are seven muscles in the orbital region, viz., (1) Levator palpebrae 

 superioris, (2) Rectus superior, (3) Rectus inferior, (4) Rectus internal, (5) Rec- 

 tus external, (6) Superior oblique, (7) Inferior oblique. All of these are attach- 

 ed to the eye-ball except the Levator palpebrae superioris. The third nerve sup- 

 plies five of these seven muscles, ail except the Superior oblique which is sup- 

 plied by the fourth, and the External rectus which is supplied by the sixth. 

 (Plate CCVI). 



The eye-ball is spheroidal in shape, but consists of the segments of two spheres, 

 a portion of the smaller sphere forming its anterior transparent part, and being 

 set on the front of the posterior segment, which is a part of the larger sphere. 



The eye-ball consists of three coats, sclerotic, choroid, and retina. 



(a) The sclerotic coat is an opaque, white, dense, fibrous, inelastic mem- 

 brane, continuous with the cornea in front, the two forming the external coat 

 of the eye-ball. 



(b) The choroid is a delicate, highly vascular membrane, forming one of 

 the coats or tunics of the eye-ball, lining the sclerotic, and lying between it and 

 the retina, with which it is in contact by its inner surface. 



(c) The retina is the innermost and chiefly nervous coat of the posterior 

 part of eyeball,between the choroid coat and vitreous humor. It may be divided 

 into ten layers. ( Plate ('('). 



The eye-ball has three refracting media, the aqueous humor, the crystalline 

 lens, the vitreous humor. 



(a) The aqueous humor is a limpid, watery fluid which fills the space be- 

 tween the cornea and the crystalline lens of the eye. 



(b) The crystalline humor or lens is a lentiform pellucid body, com- 

 posed of transparent firm substance, inclosed in a membraneous capsule and 

 situated in front of the vitreous humor and behind the iris of the eye. 



(c) The vitreous humor is a pellucid gelatine substance which fills about 

 four-filths of the hall of the eve. behind the crystalline lens. 



LESSON CVI. 



The eye-ball is composed of three investing tunics and three refracting 

 media. From without inward the tunics are (1) fibrous, consisting of (a) scele- 

 ROTIC and (b) cornea; (2) Vascular (tunica vasculosa oculi), consisting of (a) 

 choroid, (b) ciliary body, and (c) iris; (d) Nervous coat or retina consisting 

 of: (Plate (V,. 



1. Membrana limitans interna. 



'_'. Fibrous layer, consisting of nerve-fibres. 



:;. Ganglionic layer, consisting of nerve-cells. 



\. Inner molecular, or granular, layer. 



5. Inner nuclear Layer, 



6. Outer molecular, or granular, layer. 



7. ( )uter nuclear layer. 



8. Membrana limitans externa. 



9. Layer of roils and cones (Jacob's membrane). 



