AND HABITS OF MARINE TESTACEOUS MOELUSCA. 
501 
the dissection is to avoid entangling* the point of the knife in the spiral of the 
tongue. 
Having carefully removed the salivary gland, we expose a very considerable 
nervous system. A plexus, attached on either side at the base of the tentaculse, 
passes around the back of the fleshy mass, as if to secure it, being involved in 
such a quantity of a dark-coloured substance as to appear almost like a muscle. 
Two others, in which the nervous filaments are rather more distinct, are 
attached to the projecting ears of the oesophagus, and pass to the floor of the 
cavity. The whole is to be cleared away, and the parts will then appear as 
represented in fig. 5. 
In this figure, the dark fleshy mass is seen in its natural position upon the 
muscle of the spire. The tongue, marked e, passes from under it, and runs 
back to its termination in the spiral f. The oesophagus, distinguished by its 
prominence and colour, is traced from the mouth, and one of its ears is seen 
at i. Under the fleshy mass are three muscles : a small one, c, arising from 
the tongue, and inserted into the middle of the floor of the cavity ; another, d , 
arising by a double origin from either side of the insertion of the preceding, 
and running forward to blend with the sphincter of the mouth ; and a pair of 
considerable ones, which cover the base of the fleshy mass, arising from its 
posterior part on either side, and terminating by a broad insertion immediately 
below the sphincter. The last, whose situation is indicated at b, are evidently 
the muscles upon which the act of feeding depends. 
The stomach is now to be turned forward ; and with very little assistance 
from the knife, the oesophagus will be separated from its loose attachments, 
exposing the internal parts, as in fig. 6. In the centre appears a considerable 
prominence, broad and flattened behind, and narrow on its crest and in front ; 
along which the active portion of the tongue is stretched, and over which the 
lingual membrane is expanded. The back part is divided down the centre by 
a deep vertical groove, in which the continuation of the tongue is buried. 
The pharynx is furnished with a pair of strong longitudinal muscles, (h,) which 
arise from the upper part of the mouth ; and the stomach when laid open, 
presents a series of transverse prominent ridges, which cover every part, ex- 
cept a deep channel extended from the oesophagus to the intestine. 
The dissection will be completed by turning back the lingual membrane, 
3 T 
MDCCCXXXII. 
