( 9 1 5 
"vided With a Valve, which was difpofed in fuch a 
manner, as to let out what was contain’d in the Veflel, 
but to fuffer nothing to go in. In all my Obfcrva- 
tions upon the furface of the Bones, I never, but this 
one time, difcover’d fo many of thefe Veflels in fo fmall 
a compals. 
As for that Matter, which ifTues out from the Bone, 
and is carried into the Periofieum y I have difcover’d 
the fource of it to be the fpongy or cellularSubftance 
on the infide of the Bone, which is the repofitory for 
the Marrow. 
This fpongy Subftance confifls of long Particles 
clofely united and link’d together, which Particles are 
compos’d of an infinite number of fmall Veflels, Come 
running lengthwife, and others taking their courfe to- 
wards the Tides of the bony Particles. 
Thefe bony Particles, notwithflanding their great 
number of Apertures, are yet exceeding hard, and lie 
fome of them parallel, aud others perpendicular to the 
length of the Bone, 
Thole Particles, that lie perpendicular to the length 
of the Bone, have Veflels proceeding from their ends; 
and from their Tides, where they do not lie dole toge*; 
ther, proceed other Veflels, that compofe the Ccrtex y 
or fuperficial part of the Bone. And thofe bony 
Particles that lie parallel to the length of the Bone, 
fend out Veflels from their Tides, that iflue out thro’ 
the Tide of the Bone: It is impoffible for tho r e, who 
have not feen this with their own Eyes, to conceive 
the prodigious number of fmall Veflels, of which the 
cortical part of the Bone confifls ; which in fome places 
lies no thicker upon the fpongy part of the Bone, than 
a thick Hair of a Man’s Head, tho’ in other places it 
has three or four times that thicknefs. 
To 
