NO. 2 HONEY BEE^ SNODGRASS 75 



The femoro-tibial joint differs but little in the three legs of the 

 bee. Its mechanism is well exemplified in the middle leg, which, seen 

 from below (fig. 22 J), shows the two articular points (;', k) of the 

 joint and the deep membranous ventral emargination of the wall of 

 the femur. The articulations consist of two strong basal lobes of the 

 tibia (L), which fit against corresponding processes concealed within 

 the end of the femur (K, /, k). The conjunctival membrane below 

 the joint (H, J) contains a small, partly invaginated gennilcxor plate 

 (gf), to the apex of which is attached the tendon of the broad, pin- 

 nate flexor muscle of the tibia (p/) lying ventrally in the femur. 

 The fibers of the extensor muscle arise along the dorsal wall of the 

 femur (H, go), and are inserted on an axial tendon attached to the 

 recurved dorsal head of the tibia (H, L). In the hind leg the joint 

 structures are essentially the same as in the middle leg, though some- 

 what different in shape (fig. 24 G), and the tibial muscles are larger 

 (H, 112, its). 



The femur of each leg contains in addition to the tibial muscles a 

 branch of the flexor muscle of the pretarsal claws (fig. 24 H, ii/a), 

 which is inserted on the end of a long tendon {iiyAp) extending 

 through the tiliia and tarsus. Finally, there is to be found in each 

 femur a slender, tendinous thread (o) attached on the head of the 

 tibia just anterior to the extensor tendon (fig. 22 L), which extends 

 proximally in the femur, and probably belongs to a chordotonal organ 

 such as occurs in the femur of various other insects. 



The tibio-farsol joint. — The joint between the tibia and the tarsus 

 in each leg of the bee is quite different from that between any of 

 the other leg segments ; it is monocondylic, and the tarsus is movable 

 on the tibia by three muscles. The single point of articulation is 

 median and dorsal, but is concealed within the distal end of the tibia ; 

 two of the muscles are inserted respectively anterior and posterior to 

 the articulation, the third muscle is ventral. 



The essential features of the tibio-tarsal joint are the same in all 

 three legs, but structural details and the mechanism are somewhat 

 different in the hind legs. In the first and the second leg the proximal 

 end of the long basitarsus presents dorsally three knobs (fig. 22 E). 

 The middle knob (n) is the articular condyle; it is received on the 

 concave surface of a large, hook-shaped articular process (m) that 

 descends from the dorsal wall inside the end of the tibia (I, m). The 

 lateral knobs give attachment to the anterior and posterior tibial 

 muscles (E, pi", pj), which arise on the corresponding walls of the 

 tibia. In the fore leg and the middle leg the attachments of these 

 muscles on the tibia are so nearly on a level with the articular condyle 



