PHYLLIVOKA. 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- Fig.n. 

 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 Mouth mass of Helix. 

 true tongue.* 



" It is enclosed in the muscular head of the animal, 

 and is connected with the oesophagus, f. 17. b, 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. 



