EXTERNAL ANATOMY OF INSECTS. 667 



c. Femur or Humerus a . The femur or thigh is the 

 third, and usually the largest and most conspicuous joint 

 of the leg. In the hypothesis before alluded to b it is 

 considered as the analogue of the tibia of vertebrate 

 animals. With regard to the articulation of this part 

 with the trochanter, it has been sufficiently explained 

 under that head, and that with the tibia I shall treat of 

 when I come to that joint. As to the size of the thighs, 

 and their relative proportions to each other and to the 

 remaining joints of the leg, the most general law is, that 

 the anterior pair shall be the shortest and smallest, and 

 the posterior the longest and largest. With respect to the 

 remaining articulations, most commonly the thigh is longer 

 and larger than the tibia, and the tibia than the tarsus. 

 But there are numerous exceptions to both these rules. 

 With respect to the jirst, we may begin by observing that 

 the increase of the magnitude of the thigh, from the an- 

 terior to the posterior pair, is usually gradual : but in 

 many jumping insects, and likewise many that do not 

 jump, the posterior pair are suddenly and dispropor- 

 tionally thicker than the rest c . Again, in many insects 

 the anterior pair are the longest and thickest, as in Ma- 

 cropus longimanus, Bibio, Nabis, &c: in others, the in- 

 termediate exceed the rest in magnitude, as in Onitis 

 Aygulus, cupreus ; Sicusjlavipes, &c. ; in many Lamelli- 

 corns all the thighs are incrassated and nearly equal in 

 size : but in some, as Ryssonotus nebulosus M c L. d , the 

 intermediate pair are rather smaller than the rest. With 

 respect to the second, rule — in some, as in the male of 

 Hdacropus longimanus, the anterior tibia, though more 



e Plate XIV. XV. XXVII. r" . b See above, p. 591, 662. 



'• Vol. II. p. 314—. !i Linn. Trans, xii. t. xxi./. 12. 



