NO. I INSECT THORAX SNODGRASS 9I 



The musculature of the femoro-tibial joint is variable. In adult 

 insects, except Protura, however, it consists of a levator and a depres- 

 sor of the tibia (fig. 39, S, T), the former often double (fig. 40, S, S). 

 Both muscles are large and arise within the femur, though the depres- 

 sor commonly has an anterior branch arising on the ventral wall of 

 the trochanter (fig. 39, Tr). The fibers are usually inserted on 

 apodemes springing from the dorsal and ventral lips of the tibial 

 base, or arising from the membrane of the knee joint, the base o^ 

 the depressor apodeme often forming a large chitinous plate in the 

 ventral membrane of the joint. In the Protura, according to Prell 

 (1912), there are no levator muscles in the telopodite beyond the 

 trochantero-femoral joint, though Berlese describes a levator (ab- 

 ductor) of the tibia and of the tarsus. The depressor of the tibia in 

 the Protura (fig. 41 A, T) consists of several branches arising in the 

 femur and in the trochanter. In the leg of a caterpillar the tibia has 

 a levator (fig. 41 B, S) arising in the base of the femur, and a 

 depressor of three large branches (T) , two branches from the femur 

 and one from the trochanter, the group suggesting that of the tibial 

 depressors in Eoscntouion (A, T) . Apparently all insect larvse have 

 both levator and depressor nniscles of the tibia regardless of whether 

 the femoro-tibial articulation is dicondylic or monocondylic. 



The tarsus of typical adult insects is provided with both levator 

 and depressor muscles arising within the tibia (figs. 39. 40, U, V). In 

 the Protura (Prell, 1912) there is no tarsal levator, and the depressor 

 usually arises by several heads in the ti1)ia, femur, and trochanter, the 

 distribution varying according to the species. In Eoscntouion there 

 is but one long depressor of the tarsus with its origin in the trochanter 

 (fig. 41 A, V). In the caterpillar of Estigincne (fig. 41 B) there is no 

 tarsal levator, but a simple depressor (F) arises on the anterior ven- 

 tral wall of the tibia. In all insect larv?e the tibio-tarsal joint is either 

 monocondylic or lacks articular points. In a trichopteran larva, as 

 figured by Borner (1921), the tarsus has only a depressor muscle; 

 but in coleopteran larvae with a tarsus distinct from the tibia, there 

 are both levators and depressors of the tarsus (fig. 43 A, U, [')• I11 

 adult insects the tarsus is freely flexed upward, l)Ut can usually be 

 extended only in line with the axis of the tibia ; in larval insects the 

 tarsus has a greater downward motion. 



The subsegments of the tarsus are never provided with muscles, 

 evidence that the articles are not true segments. Du Porte (1920) 

 has described and figured levator muscles of the tarsal subsegments 

 in Gryllus, but this is certainly an error. Likewise, muscles of the 

 foot, or pretarsus, never have their origin in the tarsus in insects, 



