68 ON THE ANATOMY OF THE FLY. 



process is directed forwards, as is represented in the plate, but it is capable 

 of revolving like a hinge, so that when the wing is open this process is 

 directed outwards. 



Beneath the last is an irregular-shaped piece of chitine, completing the 

 outer circle of the wing joint, and uniting with the anterior superior angle 

 of the posterior lateral plate of the meso-thorax. This latter bears a pro- 

 tuberance (Plate V., fig. 12 a), filled internally with muscle, which I shall 

 call the ampulla. 



The ampulla hangs over the anterior portion of the wing joint. Its 

 posterior edge bears an irregular ring of chitine beneath the integument* 

 which supports three very remarkable processes ; the centre of this ring is 

 occupied by a loose puckered membrane. 



The most important of these processes is shaped like an inverted molar- 

 tooth (Plate V., figs. 12 & 14) ; it supports the wing pivot in its cavity^ 

 and is probably the joint upon which the wing swings, when rapidly 

 vibrating. It is excessively hard and semi-transparent, like the wing pivot, 

 I shall call it the wing-s ocket. 



In front of the wing-socket is a flattened rod, broadest at its free ex- 

 tremity, and slightly curved (Plate V. figs. 12 & 13). Its free extremity 

 is covered with a soft elastic substance, which easily separates from the 

 rod itself, which is as hard as the wing-socket. Its free extremity fits a 

 small cavity in the anterior part of the base of the tooth beneath the sub- 

 costal nervure, or wing-pivot. Its function may be to keep the wing back 

 whilst vibrating, or even to stop its vibrations, a view indicated by its 

 eoft elastic extremity. The third and last process appears to be rudimen- 

 tary, it consists of a single hardened tooth directed backwards ; I think 

 it may support the wing-pivot in some positions, but have not been able 

 to make out its use. 



The muscles attached to these parts are very numerous, and are most of 

 them furnished with fine tendons ; each muscle consists of a few fibres. They 

 arise from the several internal processes already indicated, but at present the 

 exact origin and insertion of each has not been made out. Shortly, it may 

 be said that every separate piece is furnished with at least two muscles* 

 an extensor and flexor, or an elevator and depressor as the case may be. 



The legs consist of several tubular articulations, the names 

 of which have already been given,* but the three pairs differ 

 somewhat, especially as to the coxas. 



* Page 19. 



