338 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I37 



If the "external dorsal" of Orthellia did not have its attachment to 

 the scutum demarcated from that of the "internal dorsals" by the 

 transverse suture and the posterior attachment distinguished by being 

 on the postscutellum it could not be distinguished from the "internal 

 dorsals." The transverse suture of the calypterates may not be ho- 

 mologous with that of such Nematocera as possess one (Tipulidae, 

 Trichoceridae, and Tanyderidae) ; the postscutellum is a feature of 

 the calypterates. Thus the dorsal longitudinal muscles of Anisopus 

 cannot be regarded as comprising more than a single series. As noted 

 by Tiegs (1955) these muscles comprise six large "giant" fibers (see 

 elsewhere in this paper). 



Fig. 2. — Anisopus fenestralis Scop., right half of mesothorax at midline to show 

 dorsal longitudinal (indirect flight) muscles. X 42. 



The dorsal longitudinal muscles lie on either side of the midline 

 stretching from the scutum to the mesothoracic postnotal phragma. 

 Their action is described as causing depression of the wings, indirectly. 



2. OBLIQUE DORSAL (INDIRECT FLIGHT) MUSCLE. 



Other names are: Oblique lateral dorsal muscle (Snodgrass), 

 third dorsoventral muscle (Ritter), lateral dorsal muscle (Maki), 

 oblique dorsal muscle (Bonhag), lateral oblique dorsal muscle (Mil- 

 ler in Demerec). 



When a specimen, split down the midline, has the main dorsal 

 longitudinal muscles removed, this oblique dorsal muscle comes into 

 view along with the dorsoventral indirect flight muscles ; it appears 

 to have the same function, acting as an indirect elevator of the wing. 

 It consists of two giant fibers of the same structure as those of the 



