22 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 56 



6. The Muscles of Flight 



The best way to study the muscles of flight is to make a median 

 section of the thorax to work down laterally from this, and to observe 

 with a binocular mJcroscope. The illustrations to this paper relate 

 throughout to preparations made and examined in this way. They 

 show the successive muscular layers thus rendered visible. 



Two kinds of muscles of flight are to be distinguished: indirect 

 and direct. The former act indirectly upon the wings by compressing 



m m 



d V II 



Fig. 4. Diagrammatic view of the median indirect muscles, 

 of the thorax.) 



(Median section 



ap, Mesapophysis. 



dvl, Musculus dorso-ventralis primus. 



dvll, Musculus dorso-ventralis secundus. 



lu, Air-sac. 



m, Musculus latus. 



mm, Musculus dorsalis. 



the breast longitudinally and vertically; the latter are attached to 

 the roots of the wings and move them directly. The number of 

 direct muscles is larger than is generally supposed ; in Calliphora 

 vomitoria there are no less than ten pairs. In the Libellulidse, where 

 only direct muscles of flight occur (von Lendenfeld, 1881, p. 344) » 

 these muscles are correspondingly strong. In the Diptera, where 

 the chief work of flight is performed by the indirect muscles, these 



