356 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 1 37 



the TDT muscle came beneath the axis of the coxal-trochanter articu- 

 lation a very strong pull indeed could be exerted by the TDT muscle. 

 The initiation of the return of the trochanter to a position in which 

 the TDT muscle could act as a depressor could be easily initiated by 

 the smaller but doubtless quite efifective coxal depressors of the 

 trochanter. 



In myogenesis the TDT muscle's origin is associated with the ven- 

 tral or leg imaginal bud (Zalokar, 1947; Shatoury, 1956). Shatoury 

 has ascribed a very important myogenetic controlling role to the 

 TDT muscle in the development of the indirect flight muscles in 

 Drosophila. 



The TDT muscle dififers in shape in different Diptera. In Sciara 

 (pi. I, fig. h) it is long, thin, and nearly columnar. In Tahanus it is 

 a well-developed muscle with the origin considerably larger in area 

 than in average cross section and it tapers down continuously to the 

 insertion on the tendon of the trochanter. In Calliphora (pi. i, fig. e) 

 the muscle is naturally broader at the base than at its insertion on the 

 tendon of the trochanter, but the diameter is about the same through- 

 out its length. Musca (pi. i, fig. d) has a very well developed TDT 

 muscle to which the term fan-shaped can almost be applied. 



7. THE COXOSUBALAR MUSCLE IN DIPTERA 



A muscle running from the meron of the coxa to the subalar sclerite 

 of the same segment of the pterothorax is generally regarded as one 

 of the basic muscles of the winged segment. In Diptera, Maki (1938) 

 noted the presence of such a muscle in the mesothorax of a tipulid 

 (see pi. I, fig. c) and its absence in the mesothoraces of a stratiomyiid, 

 a syrphid, a micropezid (=:calobatid), and a muscid. Tiegs (1955) 

 extended the list, noting its presence in the mesothorax of a tipulid, 

 a culicid, and a chironomid, and its absence in a tabanid, a neme- 

 strinid, a muscid, a syrphid, a bombyliid, a tachinid, a therevid, an 

 asilid, and a drosophilid. Below, it will be referred to by the abbrevia- 

 tion CS muscle. 



Bonhag (1949), noting the absence of this muscle in Tahanus as 

 contrasted with its presence in a tipulid and Mecoptera, stated his 

 belief that it was "part of the primitive ground plan of the meso- 

 thoracic musculature of Diptera." 



Details of the CS muscle in Anisopus have been given elsewhere 

 in this paper. The CS muscle of Nematocera varies greatly in size. 

 Ptychoptera has a very large muscle, and this is associated with an 

 oblique-dorsal muscle that is very much smaller than usual when 



