194 THE INTEGUMENTAL SKELETON OF THE IMAGO. 



femur (g). The flexor muscle is inserted into the syndes- 

 mosis {^fi) between the femur and tibia on the ventral surface of 

 the limb, and the extensor {ex) into the femur dorsally to the 

 articular apodemes. The movements of the femoro-tibial 

 articulation are strictly limited to flexion and extension. 



The Tarsus, or foot, consists of five joints, each contracted' at 

 its proximal extremity, and exhibiting a capitellum, or head, 

 which articulates with a concave socket on the dorsal distal 

 margin of the joint above it. The tarsal articulations are true 

 ball-and-socket joints, which permit of considerable lateral 

 movement, as well as of flexion, extension, and limited rotation. 

 The ventral margins of both the proximal and distal extremities 

 of these joints are united with the adjacent joints by loose 

 syndesmoses. (Fig. 20, o, is a diagrammatic representation of 

 this form of joint.) 



The plantar surfaces of the tarsal joints support combs of 

 stiff bristles, which are used in cleaning the surface of the 

 integument and the setas with which it is covered. The comb 

 is most conspicuous on the anterior tarsi, and is rudimentary 

 or absent on those of the intermediate legs. 



The terminal tarsal joint supports the pads, pulvilli {p), and 

 the claws, ungues {u), as well as a plate — the planta or empo- 

 dium — at its distal extremity. 



The Claws, or Ungues, are strong, curved, hollow sclerites. 

 Each has a sub-hemispherical head, which articulates with a 

 notch in a thick cordiform swelling on the under surface of the 

 dorsal aspect of the distal margin of the last tarsal joint. The 

 claws of the posterior tarsi are more slender and less curved 

 than those of the four anterior feet. 



The upper edges of the claws are united by syndesmosis 

 with the distal extremity of the last tarsal joint. 



Some writers regard the plantae, claws, and pulvilli as a 

 sixth tarsal joint ; the rudimentary tarsus of the nymph, how- 

 ever, has only five joints (Fig. 34), so that the claws and 

 pulvilli must be regarded as paired appendages of the last 

 joint. The planta is a sclerite in the extremity of the limb, 

 and not a distinct limb segment. 



