380 SENSITIVE SYSTEM. 



padded with fat. Its union with the transparent part, or cornea, is 

 so neat and perfect that one has been deemed to be a continuation 

 of the other : the sclerotica manifestly differs, however, from the 

 cornea, not only in being opaque, but in its texture and organi- 

 zation, and also in its diseases. Moreover, either maceration or 

 putrefaction disengages one from the other, and then it is demon- 

 strable that the surrounding margin of the elliptical opening of 

 the sclerotica is bevelled off, for the purpose of overlapping and 

 nicely fitting the edge of the cornea, which is also sloped off, but 

 in the contrary direction. The sclerotica is thinner upon its nasnl 

 than its temporal side, though it terminates in front in a thick- 

 ened border all round ; but it is thickest at its posterior part, near 

 the centre of which is a small circular aperture for the admission of 

 the optic nerve: this opening is situated towards the inner and 

 inferior part of the globe, and appears, when examined internally, 

 as a white cribriform spot. The internal concave surface of the 

 sclerotica is in intimate contact with the tunica choroides, from 

 which it commonly receives a dusky stain, the natural effect of 

 transudation after death : these coats are weakly connected to- 

 gether by a very delicate cellular tissue, likewise by bloodvessels 

 and nerves which find their way in great numbers to the choroid 

 coat through pinholes in the sclerotica, most numerous round 

 about the entrance of the optic nerve, and in the vicinity of the 

 corneal border in front. The sclerotica possesses this peculiarity 

 over the other ocular textures — that it retains its figure in the 

 detached state equally the same that it does when distended and 

 connected with other parts, and that it will regain its shape after 

 indentation oi distortion, immediately the pressure (should that 

 have been the cause) is removed ; even small excised portions 

 nianii'est the same retentive properties: so far, however, is this 

 from being the case with the other component parts of the eye- 

 ball, that, we shall find, there is but one of them but what is di- 

 rectly or indirectly dependent upon the sclerotica for the preser- 

 vation of its form, and that one even (the crystalline lens) is 

 unable to recover itself after its shape has once been destroyed. 

 Some anatomistsconsider this tunic to be an expansion — either a 

 laminated or an entire one — of the sheath of the optic nerve : 

 whether one or other or neither be the case, we certainly find 

 their union to be intimate, and continuity of fibre to be the unit- 

 ing medium. The sclerotic fibres, which are dense, firm, and 

 elastic, and remarkable for their whiteness, are of the same nature 

 apparently as those that compose ligaments and tendons. Thay 

 take every variety of direction, and are so strongly interwoven 

 and matted together, that no force the fingers can exert will lace- 

 rate it : indeed, they are found to decussate no generally through- 



