262 Sir Everard Home on the structure of the 
in this Paper, belong to a series of less complex structures, 
and perhaps, few animals can have a more simple mechanism 
than the leech. 
EXPLANATION OF THE PLATES. 
Plate XI. 
A view of a portion of the lamprey of the natural size, the 
organs of respiration exposed. 
The mouth is laid open, exposing the teeth. 
a. The tongue, on which there are teeth turned on one side. 
b. The cavity of the mouth. 
c. The fauces. 
d. The tube between the bags containing gills. 
e. Its termination in a loose edge at the orifice of the oeso- 
phagus. 
/. A firm cartilage in the centre of the retractor muscles 
of the tongue. 
gg. Two large salivary glands. 
hh. The cavities containing a structure like gills laid open 
through their whole extent. 
it. The external orifices of these cavities. 
kk. The internal orifices. 
//. The cartilages of the thorax. 
m. The cartilaginous pericardium. 
n. The termination of the oesophagus in the stomach. 
