PHYLLIVORA. 
57 
fourths of which is rolled into a tube, fig. 17. c; the 
posterior end of this tube is closed, its anterior ex- 
tremity expanded into a flat- 
tened or spoon-shaped form, 
which plays against the edge of 
the horny upper jaw, fig. 17. 
thus acting more in the capa- 
city of an under jaw than a 
true tongue.* 
It is enclosed in the muscular head of the animal, 
and is connected with the oesophagus, f. 17. 5, at the 
anterior end of the tube, the extended upper portion 
of the oesophagus forming the roof of the mouth, 
while the expanded surface of the tongue covers the 
lower part of the mouth. The head is usually globu- 
lar or nearly so, sometimes slightly attenuated back- 
wards. From the junction of the tube of the oeso- 
phagus and tongue, the former passes backwards 
through the head, and leaves it at its upper part 
behind (sometimes coming out almost at the top of 
the head), while the tongue takes at once a downward 
and backward direction, and protrudes its closed end 
distinctly at the lower part of the head. 
If the tubular part of the tongue be laid open 
and expanded (when it always proves of the same 
width as the naturally expanded portion), it will be 
found to be covered on its upper surface with a 
vast number of plates, each carrying one or more 
tubercles which do not stand perpendicularly to the 
* Lister and Adanson regarded the hard lingual membrane 
of Limax and Helix as a second or lower jaw. Adanson men- 
tions the teeth, and compared the “jaw ” to an etrille, Swam- 
merdam called the tongue a cartilage. 
Fig, 17. 
