448 CEPHALOPODA. 



fibres : its surface is divided into several lobes (/, g, A), partially 

 invested with a delicate and papillose membrane ; but a large 

 portion of tlie organ is covered with sharp recurved horny hook- 

 lets, so disposed that, with their assistance, the morsels of food 

 taken int# the mouth are seized and dragged backwards by a kind 

 of peristaltic motion to the commencement of the ffisophagus (z). 

 The necessity of the provision thus made for enabling the Cepha- 

 lopods to swallow the substances upon which they feed, must be at 

 once apparent ; for, seeing that the walls of the mouth are formed 

 entirely by the hard and inflexible horny beak, it is difficult to 

 conceive how deglutition could have been accomplished by any 

 other contrivance. 



(489.) Four salivary glands pour a copious supply of saliva into 

 the oral chamber : of these, two, situated on the sides of the root of 

 the tongue, give off distinct ducts, which terminate near the com- 

 mencement of the O3sophagus ; while the other pair, generally 

 larger than the superior, is lodged in the visceral sac on each side 

 of the upper part of the crop. The inferior salivary glands each 

 furnish an excretory canal ; but their two ducts soon unite into a 

 single tube (wi), which, with the oesophagus, passes through the 

 ring formed by the cranial cartilage, and, piercing the fleshy mass 

 of the mouth, opens in the neighbourhood of the spiny portion of 

 the tongue, so that the secretion furnished at this point serves to 

 moisten the aliment as it is taken up by the lingual hooks to be 

 swallowed. In Onychoteuthis two salivary glands (fig* 09, &) 

 are situated at the root of the tongue, and their ducts are pointed 

 out in the drawing by pins introduced into their orifices. 



(490.) The alimentary canal presents the same general struc- 

 ture in all the Cephalopod families. The oesophagus (fig. 208, 

 A, d',jig. 10, s), derived from the posterior part of the fleshy 

 mass of the mouth, passes through a ring formed in the cranial 

 cartilage ; or else, as in Nautiluses partially embraced by processes 

 derived therefrom. It soon dilates into a capacious crop (fig- 

 210, ), the walls of which are glandular; and, being lined with a 

 mucous membrane that is gathered into longitudinal plicae, this 

 organ readily admits of considerable dilatation. 



From the crop, a short passage (u) leads into a strong muscular 

 gizzard (v) resembling that of a granivorous bird, and lined in the 

 same manner by a thick coriaceous cuticular layer : in this gizzard, 

 therefore, the food is gradually bruised and reduced to a pultaceous 

 magma. 



