3.96 GASTEROPODA. 



contrivance. Attached to the upper part of the muscular cavity 

 that contains the oral apparatus, there is a broad horny plate, the 

 lower edge of which is free, very sharp, and slightly curved, form- 

 ing in fact a knife (Jig. 195, y), admirably adapted to divide the 

 leaves and soft parts of vegetables when they are pressed by the 

 action of the lips against its cutting edge. 



The floor of the mouth is provided with a small cartilaginous 

 tongue, covered with delicate transverse striae, and so disposed 

 that by its movements it is well calculated to assist in propelling 

 the food into the cesophagus. In many species of Gasteropoda 

 the tongue is indeed even still more efficient as an agent in deglu- 

 tition, being studded all over with minute and recurved hooks, evi- 

 dently intended to take a firmer hold of the substances swallowed. 



(431.) The cesophagus (jig* 183, e) is continued from the 

 muscular cavity (c') that encloses the dental plate, and soon dilates 

 into a wide stomachal receptacle, v 9 r, the posterior portion of which 

 is when in situ imbedded among the viscera contained in the 

 shell ; but in the figure all these parts are unfolded and separated 

 from each other. At the termination of the stomach, biliary 

 vessels (c) are inserted, and the intestine commences ; the latter 

 being a simple tube (a, e) intervolved among the masses of the 

 liver, nearly of equal diameter throughout, and presenting inter- 

 nally neither valves nor any other remarkable appearance. Ex- 

 ternally the intestine is intimately connected with the lobes of the 

 liver among which it lies imbedded, by means of a delicate cellu- 

 losity and vascular twigs passing from one to the other. The anal 

 aperture (o), when undisturbed by dissection, is placed upon the 

 right side of the neck, in the immediate vicinity of the orifice 

 (fig. 195, e ) that leads into the respiratory cavity. 



(432.) Two sets of auxiliary glands are subservient to diges- 

 tion, the salivary and the hepatic, both of which are of consider- 

 able size. 



The salivary glands are semi-transparent and of a whitish colour ; 

 they form two irregular broad ribands, which extend along the 

 sides of the stomach (v), spreading out so as to embrace a con- 

 siderable portion of its extent, and they are occasionally joined 

 together by intercommunicating processes. Two ducts, one de- 

 rived from each gland, run along the sides of the cesophagus, and 

 open into that canal close to the mouth. 



The liver is of large proportionate dimensions, and is made up 

 of four lobes (b, d) of a dark brown colour, and composed of an 



