(63 ) 
vi\. Whenfoever the motion of a bone may be made about 
onefixt point, that motion will be Sp^dcal 5 but when 
ihe motion muft be about two Poles , or an Axis^ that is ae« 
ceflaiily on a plain Ciiculer Superficies^or a Conical one. 
Tolliew the ftrengthand Momentum of a Mufclej He 
premifes fome propofitions about the FeSles, which he ap- 
plies to moft of the chief Mufcles of the body. 
He gives us likewife an account of the wonderful ftruc • 
tureofthe EacR-bone, to the r^r^&^^j* of which he attri- 
butes a greater force than to all the Mufcles that contrad 
it, as is evident from this propolitionj That If a Porter 
carry on his back a weight of 120 pounds, the power Na- 
ture exercifes by the C^r^&^^j- of th^ Fertebroe , and the 
MufcuJi extenfores of the back, is equal to the force of 
2 5585 pound; that ofthe Mufcles alone he computes to 
be 6404. pound^and obferves that the Retenrion of a joint 
ftretched out.is not f ram the Tonical a£lion of Antagonift 
Mufcles. 
Hence he goes on to deliver the various poftures of an 
Animaly which he does by affigning bis Center of Gra- 
vity in all his poffible pofitions. As in a Man ftretched 
out at length, the Center is between the Nates and Puhu. 
That a man cannot well ftand one one Heel, or the tip of 
a Toe^becaufe in thefe cafes the Line of direBion fails with- 
out his Bajis^ &c. 
That tho Birds have two feet^ yet they neither wdk nor 
ftand the fame way as a Man 5 which depends on the dif- 
ferent ftrudure of their joy nts ForFirfttheydifFer in the 
number ofthe Bones. 2. In the Form.^Jn the diftribution 
and make of their Mufcles . 4. In the Joynts themfelves. 
He demonftrates the manner how a Bird when fleeping 
fits firm ona twig, tho the Mufcles are then unaftive; 
namely by a ftrong conftridion of its Claws, and confe- 
queatly a firm comprehenfion of that Twig, neceffarily 
and Mechanically reful ting from the gravity of the Bird^ 
and the fliortnefs ofthe Tendons ot thofe Mufcles that 
contrad theGlaws. 
Thai 
