THE INTRODUCTION 
additional bones; (Tab. i. xxxi. xxxii. xxxiii.) which in Tome meafure de¬ 
termine their growth and figure; lor if they had nothing to give bounds 
to them? they would flioot out like the callus from the broken ends of a 
bone that is ill let? (Tab. 1. li.) and grow as ragged as the edges of bones 
which are joined by futures; and fometimcs epiphyfes are made ufe of to 
faifeprocefles upon bones for the infertionsof mufcles? as the trochanters 
of the thigh bones? (Tab i. xxxi. xxxii. xxxiii.) where it would weaken 
the bones too much to have procclfes raifed out of their fubflance. 
The fibres of bones? for ought that we candifcovcr from experiments 
or microfcopical obfervations? appear to be connected to each other by 
the lame means that the parts of a fibre are conne&ed? that is? by the 
flrong attraction which belongs to particles of matter in contact: but 
this cohelion of fibre to fibre is not equal to that in the parts of a fibre, 
though very nearly. Indeed? if it was? a bone would not be a ItruCture of 
fibres? but one uniform mats? like that of any pure metal? the cohefion of 
the parts of which are every way alike. Nor are the parts of bones dilpo- 
fed into vifible lamella:? ftratum fuper flratum? as many have painted; for 
though young bones may in fome places be fplit into lamella:? yet they 
not only appear one folid uniform malsto the naked eye? but even with 
a microfcopc? till we come to their inner fpongy texture? which alfo ap¬ 
pears uniform. Their texture when firft formed? is every where loole and 
fpongy, but as they increafe? they become in many places very compact 
and denfie, which refults in great meafure from the prefibre of the bellies 
of the mufcles, and other incumbent parts; as appears from the impref- 
lions they make on the furfaces of the bones? and the rough /pines that 
rife on the bones in the interlticcs of the mufcles? which are very remark¬ 
able in men who have been bred up in hard labour. In thofe parts of the 
flat bones that receive but little preflure, the outer laminx only become 
compaCf and denfe, and the middle part remains fpongy; but where the 
preflure is greateft? as on the fcapula (Tab. xxii.) and the middle of the 
ilium? (Tab. xviii.) they become in an adult? one denfe body or table, and 
are ufually thinner in thofe places than in a child before it is born. The 
cylindrical or round bones being prefled molt in their middles? become 
there very hard and ftrong? while their extremities remain fpongy? and 
dilate into large heads, which make ftronger joints? and give more room 
for the origins and infertions of the mufcles; and increafe the power 
of the mufcles, by removing their axis farther from the center of mo¬ 
tion of any joint they move. 
All the bones? except fo much of the teeth as are out of the lockets. 
