592 CEPHALOPODA. 



consequence freely admitted the preserving liquid into the interior of 

 the globe. 



(1586.) However much is still left to be ascertained by future ob- 

 servations, we learn from the above able exposition of the appearances 

 detected on examining the solitary example of a visual organ of this 

 description hitherto met with, that the eye of the Nautilus exhibits 

 every indication of inferiority of construction when compared with that 

 of the Dibranchiate tribes. Encased in no orbital cavity, and conse- 

 quently unprovided with any other muscular apparatus than the fleshy 

 pedicle whereby it is connected with the head unprotected by eyelids 

 and devoid of lacrymal appendages without either transparent cornea, 

 aqueous humour, iris, or crystalline lens and, moreover, coated inter- 

 nally with a dark pigment, apparently situated in front of the nervous 

 expansion which represents the retina, instead of behind it in the usual 

 position of the choroid tunic all these are facts calculated to arrest 

 the attention of the physiologist, and excite the surprise of every ob- 

 server who studies on a large scale this part of the animal economy. 



(1587.) The eyes of the Dibranchiate Cephalopoda are not less re- 

 markable in their construction than those of the Nautilus, and from 

 their greater complexity will require a more elaborate description. In 

 order to simplify the details connected with this portion of our subject 

 as much as possible, we shall describe separately, as forming distinct 

 parts of the ocular apparatus met with in the common Cuttle-fish (Sepia 

 officinalis), first, the orbit ; secondly, the globe of the eye ; thirdly, the 

 chamber of the optic ganglion ; and fourthly, the muscles of the visual 

 organ. 



(1588.) The orbit differs from that of all other classes of animals, 

 inasmuch as it is a cavity circumscribed on all sides and covering even 

 the front of the eye*. The bottom of the orbital cavity is cartilaginous, 

 being partially formed by a process derived from the cranial cartilage ; 

 but elsewhere it is made up of the common fleshy integument of the 

 body (fig. 292, d d, e): becoming gradually attenuated, the skin (b) 

 passes over the anterior portion of the eye, where, being transparent (/), 

 it represents the cornea, although it has no connexion with the eye-ball 

 itself. Beneath the cornea the integument again becomes opake, and 

 forms a thickened fold (a), which might be considered as the rudiment 

 of an under eyelid. The orbit therefore forms a complete capsule, en- 

 closing the whole of the apparatus of vision. 



(1589.) The globe of the eye fills up the anterior part of the orbital 

 chamber, and is remarkable from having no cornea properly so called ; 

 so that, on raising the transparent skin (/) which forms the exterior 

 wall of the orbit and supplies the place of the cornea, the prominent 



* Descriptive and Illustrated Catalogue of the Physiological Series of Compara- 

 tive Anatomy contained in the Museum of the Koyal College of Surgeons of England, 

 vol. iii. part 1. pi. 52. 



