352 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL, 1 37 



4-7 (Weber, 1928, followed by Hasken, 1939, and others, especially 

 workers in Germany) ; tergal depressor of trochanter (Maki, 1938, 

 followed by Niiesch, 1953 ; Smart, 1957, 1958; and others) ; 4th dor- 

 soventral muscle or trochanter muscle (Ritter, 1911) ; depressor of 

 trochanter muscle (Bonhag, 1949) ; "long extenseur . . . insere au 

 trochanter" (Kunckel d'Herculais, 1875-1881) ; tergal-trochantinal 

 muscle (Kelsey, 1957). 



Maki's (1938) term is the most convenient. Below, the muscle 

 will be referred to by the abbreviation TDT muscle. It is not present 

 in the musculature of Anisopus described earlier in the present paper. 

 In Diptera, when present, the TDT muscle is quite distinctive. It 

 originates on the scutum of the mesothorax and inserts on the mesial 

 depressor apodeme of the trochanter of the mesothoracic leg proximal 

 to the axis of the coxotrochanteral articulation. Contraction results 

 in a depression or straightening out of the femur which, if not fused 

 to the trochanter, is attached thereto by a very limited articulation. 



The TDT muscle is present in insects possessing a less specialized 

 thorax than the Diptera, and it does seem, in fact, that such a muscle 

 is to be regarded as one of the fundamental muscles of the winged 

 thoracic segment if not of the hexapod limbed thoracic segment re- 

 gardless of its condition as to wings; Maki (1938) found a TDT 

 muscle present in all the thoracic segments of Lepisma. 



The condition in the cockroach {Periplaneta americana) has been 

 described by Carbonell (1947), and Snodgrass (1952) has concurred 

 with Carbonell's description. According to Carbonell the following 

 muscles act as depressors of the trochanter in the segments of the 

 pterothorax : 



A. Inserting on the mesial tendon of the trochanter : 



1. Tergal fascicle (135a) ; origin on tergum. 



2. Sternal fascicle (i3Sb) ; origin on sternal apophysis. 



3. Basalar fascicle (135c) ; origin on basalar sclerite. 



4. Coxal fascicle (i35d) ; origin on mesial coxal wall. 



5. Coxal fascicle (i35e) ; origin on anterior coxal rim. 



B. Inserting otherwise on the trochanter: 



1. Posterior coxal depressor (136); origin on posterior rim of coxa; 



inserts on independent apodeme posterior to mesial tendon. 



2. Anterior coxal depressor (137) ; origin on mesial part of coxa; in- 



serts on independent apodeme anterior to mesial tendon. 



(The numbers in parentheses are those used in Carbonell's paper.) 



In the mesothorax of the locust or grasshopper (Albrecht, 1953 ; 

 Snodgrass, 1935, etc.) conditions resemble those found in the cock- 

 roach except that there are two muscles with origins on the scutum 



