THE INTRODUCTION 
birds, the bones of their wings, and for the fame reafon their quills have 
very large cavities. But the bones in the legs of all animals arc more folid, 
being formed to fupport weight; and mens bodies being fupported by 
two limbs, the bones of thofe limbs are therefore made more folid than 
thofe of quadrupeds. Infects and molt of the finalleft animals, have {hells 
inftcad of bones like loblters, which ferve them alfo for defence ; and the 
mufcles being inferted into the {hells at a greater difiance from the center 
of motion of each joint than in animals that have bones, their motions are 
necellarily flower and ftronger as well as more Ample; therefore in this 
fort of animals, quickneis of motion, where it is wanted, is procur’d by a 
number of joints, as may befeen ; n the legs of a flea; and variety of mo¬ 
tions by joints with different directions, as may be obferv’d in a lobfier. 
In a fraCturcd bone, in which the fame kind of matter that ollified the 
bones at flrfl is thrown out from the broken ends of a bone, there is form¬ 
ed a mafs of callous matter, of equal folidity with any part of the bone, 
and of equal or greater diameter, which will make the ftrength of the 
bone in that place greater than it was before; which is very convenient, 
for bones when broke, are leldom or never fet in fo good a direction as 
that in which they were firfl formed, and therefore they would be more 
liable to be broke in the lame place again, and would be reunited with 
greater difficulty, and lometimes not at all, becaule the callus being lels 
vafcular than a bone, it does not fo ealily admit the oflifle matter to flow 
through it to form a new callus. 
Bones that are without motion, as thofe ot the fcull, the ofla innomi- 
nata, 8cc. alio bones with their epiphyfes, when they meet, prefs into 
each other, and form futures, which foon difappear in thofe that join, 
while their oflifle matter is foft; but thofe that grow harder before they 
meet, prefs more rudely into each other, and make more uneven futures, ' 
fome of which in the fcull endure to the greatefi age : (Tab. iii. iv. v. vi.) 
And lometimes while a bone is oflifying from its center, a diflant part be¬ 
gins a newoflification and forms a difiinCt bone, which may happen to be 
of any figure. Thefe bones are ofteneft found in the lambdoidal future, 
and are called ofla triquetra. (Tab. vi.) But the ends or Aides of bones that 
are intended for motion, are hindered from uniting, by the cartilages 
which cover them; for when thefe cartilages are eroded the bones very 
readily unite. (Tab. xliii. xliv. xlvii li. liv.) This diilemper is called an- 
chylofis. * 
The ends of all the bones that are articulated for very manifeft motions, 
or that are not placed againit other bones, are tipped with epiphyfes, or 
