NO. 2 THORACIC MECHANISM OF A GRASSHOPPER SNODGRASS 83 



femur arising in the trochanter are small or absent. In Dissosteira 

 a posterior, or reductor, muscle only is present in the trochanter of 

 the first leg (fig. 36 A, 72) and in that of the second leg. In the hind 

 leg there is no movement at the trochantero-femoral joint and femoral 

 muscles are lacking. The usual flexion between the trochanter and 

 the femur of insects is anterior and posterior (production and re- 

 duction), and generally only a reductor muscle is present, called the 

 "rotator" of the femur by some writers (Morison, 1927; Weber, 

 1929). 



The femur is occupied mostly by the tibial muscles (fig. 44, S, T), 

 but it contains also the most proximal branch of the flexor of the 

 claws (X). The tibial musculature comprises levator muscles (S) 

 and depressor muscles (T). In Dissosteira there are two levator 

 muscles in each leg, a larger posterior one (fig. 36 E, 106, F, 135), 

 and a very small anterior one (E. lOj, F, 134) . In the fore and middle 

 legs the depressor of the tibia (fig. 36 B, C, loy) is larger than the 

 levator, and it has a basal branch arising in the trochanter (B). In 

 the hind leg the relative proportions of the two muscles are reversed, 

 the posterior levator, or extensor, of the tibia consisting of the great 

 masses of fibers arising on the ridged anterior and posterior walls of 

 the femur (fig. 39, 133a, 133b), and including smaller branches 

 {133c) arising on the dorsal wall in the distal part of the femur. The 

 anterior levator of the tibia in each leg consists of a very slender 

 bundle of fibers arising anteriorly in the base of the femur (fig. 36 A, 

 75) and inserted by a long, thread-like apodeme on the head of the 

 tibia (E, 103AP, F, 134AP). 



The tibiae contain the levator and depressor muscles of the tarsus, 

 and the tibial branches of the flexor of the claws. The tarsal muscles 

 are relatively largest in the fore and middle legs of Dissosteira; in the 

 hind leg they occupy only the distal part of the tibia (fig. 39, 13/, 138). 



The tarsus contains no muscles, the tarsal segments, as before 

 noted, being flexible upon one another but not independently movable. 

 This condition pertains to all insects. The tarsus is traversed by the 

 " tendon," or thread-like apodeme, of the flexor of the claws (figs. 

 39, 139AP, 44, x) . 



The claws of insects are provided with only a flexor, or rectractor, 

 muscle, which is the depressor of the pretarsus (fig. 44 X), or the 

 homologue of the depressor of the dactylopodite in arthropods gen- 

 erally. The fibers of the claw muscle arise in several groups in the 

 tibia and femur, and are inserted on a long tendon-like apodeme that 

 arises from the base of the unguitractor plate (fig. 42 C, Utr) and 



