-20 TOPOGRAPHICAL ANATOMY OF THE 



head, the retractors or depressors of the prosternum, the 

 muscles between the furca of the meso- and metasternum, and 

 the inferior recti of the abdomen, but that the form and size of 

 these is greatly modified, especially in the thorax. In like 

 manner, he adds, the dorsal recti are replaced by the elevators of 

 the head, elevators of the prothorax and scutellum, and the 

 dorsal abdominal muscles. 



3. The Muscles of the Wings. Straus Durckheim regards these 

 as part of the inter-segmental system. They are a set of lateral 

 cutaneous muscles, and it is possible they represent the lateral 

 and dorsal inter-segmental muscles of the larva. They are, 

 however, so complex that I have some hesitation in including 

 them in that class, more especially as they are inserted 

 directly into the wing-sclerites. They may be termed elevators, 

 depressors, rotators, and flexors of the anterior and posterior 

 wing-roots. As I have not been able to establish their indi- 

 vidual actions, I shall content myself with a short description 

 of the origin and insertion of the principal muscles which 

 act on the wing-roots, merely observing that numerous small 

 fasciculi of muscle fibres are found uniting the various wing- 

 sclerites with each other and with the thoracic wall. 



The largest wing-muscle, musculus lateralis, is rhomboid in 

 form. It arises from the lateral plate, and is inserted into the 

 long process of the parapteron. 



The musculus accessorius arises from the dorso-pleural ridge, 

 and is inserted into the parapteron. Both muscles draw the 

 long process of the parapteron forwards and flex the wing 

 in flight (see mechanism of flight, p. 204). 



The muscles which arise from the long process of the parap- 

 teron appear as a continuation of the lateralis and accessorius ; 

 they are inserted into the sub-epaulet and remigium. A muscle 

 arises from the great ampulla, which is inserted into the dens. 

 This is inserted into a cupule in Volucella, and produces 

 rotation of the wing plane according to Kiinckel d'Herculais 

 [25]. I am unable to adduce any evidence in favour of this 

 view, and am rather inclined to regard it as the elevator of 

 the wing. 



