CEPHALOPODA. 



353 



tilaginous sclerotic, it forms a ciliary plicated zone, which penetrates 

 the groove of the crystalline lens. 



The inner surface of the retina is covered by a layer of dark 

 pigment, which is penetrated by the papillae of the retina. The 

 vitreous humour has a distinct and strong hyaloid coat. The crys- 

 talline lens is of large size, and consists of two distinct parts ; the 

 anterior or smaller moiety being the segment of a larger sphere, and 

 the posterior that of a smaller sphere : they are separated by delicate 

 transparent membranes continued from the ciliary body. The lens 

 presents the same denticulated fibrous structure arranged in con- 

 centric laminae, as in the higher animals. 



The large optic ganglion is imbedded in a white lobular sub- 

 stance, which defends it from the pressure of the muscles of the eye- 

 ball. These consist of three straight muscles and one oblique, which 

 take their origin from the orbital cartilages, and expand upon the 

 sclerotic tunic of the eyeball. 'J'he cornea of the cuttle-fish is per- 

 forated by a minute hole near the inner or anterior margin. In the 

 Octopus the corresiDonding aperture is somewhat larger, and situate 

 more in the axis of vision. In the Calamaries the corneal aperture 

 is still larger, of a vertically oblong form, and the capsule of the 

 crystalline lens, which projects through the sclerotic aperture, is 

 immediately exposed to the sea water. 



The dibranchiate Cephalopods are, without exception, predatory and 



carnivorous animals. We have seen 

 that they are endowed with for- 

 midable organs for seizing and over- 

 coming the struggles of a living 

 prey, and their strong sharp hooked 

 jaws are well adapted for de- 

 stroying and lacerating them when 

 caught. The jaws {fig. 136. k, I) 

 are sheathed upon a firm fleshy sub- 

 stance, the fibres of which are so 

 attached to the base of the mandibles 

 as to open them ; their closure is 

 effected by fasciculi of muscular 

 fibres which surround them exter« 

 nally. 



The tongue is partially covered 

 with a horny plate beset with re- 

 curved spines, which must assist in 

 the further comminution and deglu- 

 tition of the food. The fauces are also provided with spinigerous folds 



A A 



Octopus. 



