SAA EXTERNAL ANATOMY OF INSECTS. 
part is a long piece between the arms, shaped like the 
human thighbone or ¢zbia, being more slender in the 
middle and widest at the ends, and which is of a much 
harder substance than the rest of the antepectus, and 
forms the lower termination of a singular machine which 
will before long be noticed. In many bugs (Geocorise,) 
instead of being elevated, the three portions of the ster- 
num are hollowed out into a longitudinal groove, in 
which the promuscis when unemployed reposes. 
The most conspicuous and remarkable appendages of 
the manitrunk, are the brachia or arms. I shall not, 
however, enter into the full consideration of these, as they 
consist numerically of the same parts, till I treat of the 
legs in general. Here it will only be necessary to assign 
my reasons for calling them by a distinct denomination. 
In this I think I am authorized, not only by the example 
of Linné, who occasionally found it necessary to do this 2, 
and more particularly by the ancient notion that this 
pair of organs in insects were not to be reckoned as legs®, 
but likewise from their different position and functions. 
They are so inserted in the antepectus as to point towards 
the head, whereas the other two pair point to the anus. 
With regard to their functions, besides being ambula- 
tory, and supporting the manitrunk in walking, they are 
applied to many other purposes independent of that of- 
fice,—thus they are eminently the scansory or climbing 
legs in almost all insects; in most Euwtrechina, by means 
of the notch and calcar‘, they are prehensory legs; in 
* Syst. Nat. i. Cancer. Scorpio. 
> Moses, when he describes insects as going upon four legs, evi- 
dently considers the anterior pair as arms ; Bochart does the same. 
Levit. xi. 20—. Mierozoic. 1. 497, 
© PratE XXVII. Fic. 31. 
