EXTERNAL ANATOMY OF INSECTS. 671 



of the thigh a ; and upon these the tibia turns, with a 

 semirotatory motion up and down as upon a pair of pivots: 

 at the same time the mola or head of the latter joint, 

 which has often a flexure so as to form an elbow with the 

 rest of it, inosculates in the gonytheca, and is also sus- 

 pended by ligament to the orifice through which the 

 muscles, nerves, and bronchia? are transmitted: so that 

 in fact the articulation, strictly speaking, belongs exclu- 

 sively to none of the kinds observable in vertebrate ani- 

 mals, but partakes of several, and may properly be de- 

 nominated amixed articulation, — a term applicable in nu- 

 merous instances also to the other articulations of the legs 

 of insects. In the different Orders some variations in this 

 respect take place, — I will notice some of the most re- 

 markable. In no Coleopterous insects is the structure 

 more distinctly visible than in the larger Lamellicorns. 

 In Copris bucephalus, for instance, if you divide the thigh 

 longitudinally, you will find on each side, at the head, 

 that it is furnished with a nearly hemispherical protube- 

 rance, perforated in the centre for the transmission of 

 muscles, and surrounded externally by a ridge, leaving a 

 semicircular cavity between them b : if you next examine 

 the tibia, after having extracted it, you will find on each 

 side, at the base, a cavity corresponding with the protu- 

 berance of the thigh which it receives, having likewise a 

 central orifice, and surrounded by a semicircular ridge 

 corresponding with the cavity in the thigh in which it 

 acts : below this ridge another cavity, forming a small 

 segment of a circle, receives the ridge of the thigh . You 

 will observe that the ridge of the tibia represents the 



a Plate XXVII. Fig. 15. r'". h Ibid. Fig. 11. r" . 



c Ibid. Fig. 10. f". 



