ANATOMY AND PHYSIOLOGY. 97 
showing how considerable a portion of its cavity 
they occupied. But we may learn more of their 
form and connections by examining them in the 
recent state. Thus displayed they appear of-a red- 
dish yellow colour, they are freely supplied with 
tracheee, and their fibres have the microscopic cha- 
racters of involuntary muscle. They have no lateral 
attachments, they simply cross the thorax, one end 
being attached to the wall on one side, and the other 
end to the opposite side. These are the muscles of 
flight. No more simple arrangement for driving the 
wings could possibly be conceived, not even in insect 
mechanism. Thus, one pair start from the inside of 
the scutellum of the prothorax, and, descending as 
they pass backwards, are inserted into the scutum of 
the metathorax, whose long cusp seems adapted to 
receive them. By their contraction the first and last 
segments of the thorax are approximated, and the 
intermediate segment, with which they have no con- 
nection, is thrown up in an arch, and the wings are 
simultaneously depressed. The other pair lie outside 
these, and cross their direction. They start from the 
outer end of the scutellum of the meso-thorax, and 
passing downwards and forwards, are attached on 
the firm front edge of the thorax; the scutellum of 
the pro-thorax again furnishing the point of resist- 
ance. The arch of the back, which was raised by 
the action of the other pair, is depressed by these, 
and simultaneously the wings are elevated. From 
their action on the wings, though they are not 
directly connected with them, these two pair of 
muscles take their names, as the elevators and de- 
pressors of the wings respectively. 
H 
