30 



DIGESTIVE SYSTEM. 



The following is the lies! method of dissecting 1 out the 

 alimentary canal : 



1. Remove the funnel from the ventral surface of 

 the head. 



2. Cut down the web between the two ventral arms, 

 beginning anteriorly, and continue the cut down along 

 the ventral surface of the head, thus exposing the Buccal 

 bulb and the cartilage surrounding the brain. 



•'!. Loosen the intestine from the liver, dissecting 

 out the ink sac from its place on the latter, so as to 

 enable the intestine to be tinned back. 



4. Loosen the liver at the sides, where it is connected 

 to the cephalopeda] muscles, by cutting through the 

 visceral envelope, and then turn the liver forwards 

 (PI. V, fig. 38a). The organs enclosed in the visceral sac 

 are now exposed. PL IV, fig. 17, represents the alimentary 

 canal, entirely dissected away from the surrounding 

 tissues, to give a clear representation of the relations of 

 the various parts. The alimentary canal is essentially a 

 U-shaped tube, the ventral limb of the U being the 

 shorter, and the anus being approximated to the mouth. 



The Mouth is situated in the centre of the oral and 

 anterior surface of the arms (PL II, fig. 5). It is 

 circular, about 12 mm. to 22 mm. in diameter in large 

 specimens, and is surrounded by a circular lip the edge 

 of which is furnished with short finger-like papillae 

 (PI. IV, tig. IT, ///.; PI. II, tig. li, /.). The external 

 surface of the lip is continuous with that of the web, and 

 only marked off from it by a deep groove (tig. (i, </r x ). 

 This edge of the web forms a kind of contractile outer lip. 

 The mouth leads into a cavity with very thick and 

 muscular walls. This is the Pharynx and the oval 



