EXTERNAL ANATOMY OF INSECTS. 671 
segment of a circle. In these also the protuberance of 
the thigh is more minute, and its ridge is received by a 
cavity of the ¢zbza nearly semicircular ; in Geotrupes the 
articulation is not very different, though on a reduced 
scale; in Cordylia Palmarum the lateral condyles of the 
tibie are flatter and broader”; and the articulation not 
being quite so complex, this joint is kept steady by an 
intermediate process observable in the gonytheca®. From 
the above description it appears that the dislocation of the 
tibia is effectually prevented in the Lamellicorns by the 
protuberance and ridge of the thigh working in their cor- 
responding cavities, while the condyle of that part turns 
with a rotatory motion in the cavity of the thigh. In the 
Orthoptera Order the tzbia is suspended by a ligament, 
in the gonytheca the lateral condyles, which are very 
prominent, working in a sinus of that part*. The sub- 
sequent Orders exhibit no very striking variations from 
these types of articulation, I shall therefore not detain 
you longer upon this head. 
With regard to the proportions and magnitude of the 
joint we are considering,—the most general law is, that 
the anterior pair should be shorter and more slender 
than the intermediate ; and the intermediate than the pos- 
terior; and that all the ¢zbz@ should be shorter and more 
slender than the thighs, and longer and thicker than the 
tarst. Various exceptions, however, to this rule in all 
these cases might be produced ; but I shall only observe 
® Pirate XXVII. Fic. 8. Thigh. a. Protuberance.b. Semicircular 
cavity. c. Ridge. Fic. 9. Tibia. a. Central cavity. b. Ridge. c. Exte- 
rior cavity. b Tbid. Fie. 6. a. © Tbid. Fie. 7. a. 
4 Tbid. Fic. 15. Thigh of Locusta, a. Sinus in which the condyle 
of the tibia works. Fic. 16. tibia of Do. aa. Lateral condyles. b. In- 
termediate one. 
