76 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 82 



The trochanters. — The trochanteral segments of the prothoracic and 

 mesothoracic legs have the usual form of the trochanter in insects, each 

 being a short segment articulating as just noted with the coxa, and 

 united distally with the femur. The trochantero-femoral union has an 

 obliquely vertical hinge line and is perhaps slightly movable, since a 

 femoral reductor muscle is present in each of the first and second legs 

 (fig. 36 A, 7^). The trochanter of the hind leg is a short ring-like 

 segment (fig. 36 D, Tr) expanded on the posterior (mesal) surface, 

 but so narrow externally as to be scarcely perceptible here (fig. 39, 

 Tr) between the coxa and the base of the femur. It is immovably con- 

 nected with the femur but not fused with it, and there is no trochantero- 

 femoral muscle in the hind leg (fig. 39 A). The apodeines of the leva- 

 tor and depressor muscles of the trochanter arise from small sclerites 

 at the base of the trochanter in the dorsal and ventral articular mem- 

 branes (fig. 36 D). 



The femora. — In the first and the middle leg the femur is a simple 

 elongate segment (fig. 40, Fin) somewhat flattened in its antero- 

 posterior diameter (fig. 36 C). At the distal end of the femur the 

 anterior wall is expanded into a broad lobe that conceals the anterior 

 femoro-tibial articulation (fig. 36 E, /) ; the ventral wall is deeply 

 emarginate and occupied by an ample articular membrane (fig. 36 B) 

 which allows a free flexion of the tibia beneath the femur. 



The femur of the hind leg (fig. 39, Fm) contains the principal leap- 

 ing muscles, which are the extensors of the tibiae {135) ; the hind 

 femur is consequently greatly enlarged and is provided with special 

 structural features. Its length is more than twice that of the middle 

 femur, and its greatest vertical diameter is equal to the length of the 

 prothoracic femur. The flat anterior and posterior surfaces (fig. 39 B) 

 are ridged longitudinally above and below, and the space between is 

 marked by the " fish-bone " pattern of a double series of oblique 

 ridges. The latter separate the lines of attachment of the fiber bundles 

 of the extensor muscles of the tibia on the inner walls of the femur 

 (%■ 39» ^35^)- The distal end of the hind femur (fig. 36 F) 

 is structurally similar to that of the first and second femora (E), 

 but its anterior and posterior walls are strengthened by strongly 

 sclerotized plates. 



The tibiae. — The tibiae are of similar form and structure in all the 

 legs, each being a slender shaft used as a lever rather than as a con- 

 tainer for muscles, and so constnicted that it can be folded beneath the 

 femur. The femoro-tibial articulation is a strong dicondylic hinge 

 (fig. 36 E, F, /, in), and the dorsal lip of the tibial base projects well 

 within the end of the femur to give an efficient leverage to the extensor 



