1921] Uichanco — Movement of Tarsi in Apliids 65 



from the ental wall of the first tarsal segment (Plate IV, figures 

 3 and 5. I). This projection is connected at the apex and sides 

 with the articular membrane (Plate IV, figures 3 and 5. J), and 

 will be described presentl3^ The ectal wall of the first tarsal seg- 

 ment is very short, and is broadly and deeply cleft at the proximal 

 margin, forming an outer, round- top, subconical process, which fits 

 rather snugly into a groove at the ectodistal margin of the tibia. 

 This arrangement (Plate IV, figures 3 and i. G) serves as the 

 single hinge on which the tarsus moves, a condition contrasting 

 with that of the adjoining segment, the tibia, since the latter, as 

 pointed out by Woodworth (1908), moves on two hinges, situated 

 on either side at its junction with the femur. At its ento- and 

 lateroproximal sides, the first tarsal segment fits telescopically into 

 the thickly chitinized distal wall of the tibia (Plate IV, figures 3 

 and 5). When the tarsus is extended, the intervening space is widest 

 between the ental walls of the two segments and narrows do\vn ecto- 

 laterally into the hinge. The proximal margin of the .first tarsal seg- 

 ment apparently first snngly into the distal rim of the tibia when the 

 former is flexed outward. The cuticular nienil)rane connecting the 

 proximal margin of the first tarsal segment with the distal margin 

 of the tibia (Plate IV, figures 3 and 5. J) is a continuation of 

 the cuticula of the leg and is very flexible owing to its being only 

 thinly chitinized. It is widest entally and narrows ectolaterally 

 into the hinge, remotely assuming when stretched a semilunar 

 shape. The darker appearance of a small area immediately adjoin- 

 ing the tarsal projection, which has been referred to above, indi- 

 cates a marked reinforcement in this region. 



As has been mentioned in the foregoing paragraphs, a subconical 

 projection at the entoproximal margin of the first tarsal segment 

 serves as the base for the insertion of the extensor tarsi. This 

 muscle, as far as I could make out, both in the fresh preparations 

 and in balsam mounts, has its origin within the ectal wall of the 

 tibia, near the proxinuil end of the latter (Plate IV, figures 1 and 

 2. E). The body of the muscle is at the subdistal portion. This 

 is a short, spindle-shaped mass, which is readily distinguishable 

 through the tibial wall in whole mounts (Plate IV, figure 3. E). 



