AND HABITS OF MARINE TESTACEOUS MOLLUSCA. 
509 
instrument to be conveniently received within a membranous sheath. Into 
this sheath the muscles are inserted ; and the tongue, issuing from its opening, 
is expanded and stretched over two cartilaginous points. A pair of small mus- 
cles inserted into the extremity of the tongue maintain it firmly in its position. 
The tongue, with its apparatus of muscles, is contained within a strong 
membranous tube, which, at its posterior extremity, is doubled back upon 
itself ; thus presenting a containing and a contained portion, so disposed, that 
in projecting the trunk, the contained portion is elongated at the expense of 
the other. The trunk is projected by a series of annular muscles, closely set 
along the whole of the containing tube ; and it is retracted by a multitude of 
longitudinal ones, which, arising from either side of the cavity of the body, are 
inserted along this tube over their antagonists. The active extremity of the 
tongue is embraced and projected by a funnel-shaped muscle, arising from 
around the aperture of the tube, and which, at its upper part, is blended with 
the pharynx. The oesophagus rests upon the muscles of the tongue, and 
issuing from the extremity of the trunk, is doubled, and runs forward as far 
as the origin, or attachment of the containing tube ; then, forming a second 
double, it passes back to the stomach. Such a mechanism was necessary, to 
allow the oesophagus to be projected with the trunk. 
The muscular apparatus of the tongue is supported by a part which I shall 
call “ the base.” It presents the section of a cylinder, secured by two mus- 
cular crura. Its structure is chiefly membranous, with transverse muscular 
fibres, and with a double muscular column on either side. The inner columns 
are united at about a line from the point of the base, and their margins are 
free along their whole length ; but the outer columns extend to the extremity 
of the base, and being tipped with cartilage, form the support over which the 
tongue is stretched. The opposite margins of the base itself are connected 
with transverse muscular bands, beneath which they give origin to five pairs 
of oblique muscles, which are inserted into the sheath of the tongue. A mass 
of longitudinal muscles pass between the crura of the base to be inserted into 
the back and sides of the sheath. 
After this general description, the mechanism of the trunk will be suffi- 
ciently understood by a reference to the figures which illustrate the succes- 
sive stages of a dissection. In fig. 14. we have the Buccinum cleared from tne 
3 u 
MDCCCXXXII. 
