AND HABITS OF MARINE TESTACEOUS MOLLUSCA. 
499 
of the lingual membrane, may be considered as distinct muscles, and I have 
figured them accordingly (c, fig. 3.), for they are readily distinguished in their 
course, and admit of being displayed separately by dissection. The action of 
the whole mass will project, and expand the jaws, and at the same time raise 
and throw forward the tongue. The jaws are closed by the transverse muscle, 
(i d , fig. 2.) ; and the portion of food they have seized is cut away by a retraction 
of the tongue, effected by a third pair of muscles inserted into its lower part, 
(e, fig. 2 and 3.), and which, arising from the accessory cartilages, pass around 
the jaws, and run forward and upward to their insertion. 
The teeth are rolled in a longitudinal direction, and to such an extent, that 
their inserted as well as their free edges are directed backward. Thus they 
form so many springs, which, yielding at first to the resistance of the food, 
will afterwards, by their elasticity, throw back towards the stomach the por- 
tion they have separated. 
The stomach rests upon the jaws, opening directly over their active portion, 
without the intervention of any oesophagus. A pair of triangular lips project 
from its opening, and dip between the jaws to receive the food. In front of 
these is a double semi-cartilaginous valve, resting upon the fore part of the 
jaw, apparently furnished with some minute muscles, and which appears cal- 
culated, not merely to prevent the escape of any fragments of food, but also to 
bring them within reach of the lips. A pair of prominent parallel ridges are 
continued backward from the lips into the stomach for two thirds of its length, 
which, as they form a complete tube by closing their edges, may be considered 
as an internal oesophagus. I am not aware that a structure corresponding 
generally to this has been previously noticed. 
To display all these parts, the mantle and spire are first to be removed, and 
the integuments of the body divided from the muscle of the spire on either 
side as far as the tentaculae. The extremity of the tongue, which crosses the 
body from right to left, a little behind the jaws, is now to be disengaged. The 
detached integuments, with the viscera adhering to them, are next turned for- 
ward as far as the attachment of the stomach to the jaws ; in doing which we 
divide a small muscle on either side, which secures the stomach. Raising the 
jaws by the extremity of the tongue, and dividing some delicate ligaments 
which connect them with the floor of the cavity, we have brought into view 
