286 



Description of the Eye of the Cuttle Fish, 



the opening, the skin is reflected like the conjunctiva in man ; 

 but does not so suddenly pass upon the eyeball, which is conse- 

 quently covered by it to a greater extent. It is very thin at its 

 reflection on the eyeball, but afterwards becomes somewhat 

 stronger, and again thin at the margin of the aperture, where 

 the cornea is wanting. Here it joins a membrane, which may 

 be called the iris, as its relations are exactly the same as those 

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The sclerotic is divided posteriorly into two layers, a a,* (io?^ 

 the annexed figure,) between which the ganglion-like optic nerve 

 6, and a peculiar white lobulated body, c, are contained. It is 

 here perforated by a great number of holes, for the passage of 

 the filaments of the optic nerve, which, at their origin, cross 

 each other. Anteriorly, the sclerotic is open, so as to make it- 

 appear that the cornea is wanting; but this, I am inclined Iq. 

 suppose, is not exactly the case, and would rather say, that the 

 cornea is present, but perforated in the middle ; all that part of 

 the sclerotic between dd, which I consider as the ciliary ligament, 

 and the opening through which the crystalline lens projects, 

 appearing to be analogous to the circumference of the cornea. 



A choroid is altogether wanting, unless a delicate membrane, 

 ee, which arises from the inside of the most projecting part of 

 the sclerotic, may be considered to be a rudiment of this coat. 

 It proceeds forwards as far as d, the ciliary ligament, after 

 having joined the fibrous, or outer layer of the retina. When 

 the sclerotic is removed, we see what has been termed the 

 nervous part of the retina, but this, I think, should not be 

 called any part of the retina, being only the filaments of the optioju 

 nerve, before their extremities have passed through ff, th^v, 

 fibrous layer of the retina, to terminate in the nervous part^ii 

 which is distinguished by the short lines. The nervous part of 

 the retina, the inner surface of which is covered by a dark 

 purple pigment, proceeds forwards as far as the great circum- 

 ference of the eyeball, ^, where it and the pigment terminate. 

 At this point, the hyaloid membrane, h, which differs from that 

 of the higher animals, in not entirely surrounding the vitreous 



* Cuvicr considers the outer' layer as a peculiar membrane.' -*"'-'--^- 



