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nution of the bulk of the tortoife ; and it is probable 
that when the tortoife endeavoured to fink to the 
bottom, the water fell in the pipe, becaufe the animal 
lcfiened its bulk by the contraction of its mufcles ; and 
that the water rofe by the flackening of the mufcles, 
which, ceafingto comprefs the lungs, permitted it to 
return to its firfi: fize, and rendered the whole body 
of the tortoife lighter. I have, in many kinds of 
fifii, difieCted their fwimming bladders, and found 
that in great and fmall thefe are vetted with a ttrong 
mufcular membrane, which they are capable of 
contracting and dilating at will, whereby they are 
able to comprefs or expand the column of air within 
very confiderably ; this bears fome analogy to the 
detrufor mufcle of the human urinary bladder, in 
contracting itfelf for the expulfion of the urine. 
Tab. X. Fig. i. Reprefents the fituation and 
inclofure of the afpera arteria of the wild fwan, in a 
lateral view. 
2. A view of the fame, with its progrefs within the 
thorax upon the fternum. 
3. The afpera arteria of the Indian cock. 
Tab. XI. Fig. 4. A lateral view of the afpera 
arteria of a crane, as fituated in the cavity formed in 
the fternum. 
5. Shews the fleCtion of the afpera arteria of the 
Numidian crane. 
6. The biffid afpera arteria of the land tortoife. 
Received 
