IN THE HUMAN FRAME. 
57 
Had it consisted of three or four bones only, in bending 
the body the spinal marrow must have been bruised at 
every angle. The reader need not be told, that these inter¬ 
vening cartilages are gristles; and he may see them in 
perfection in a loin of veal. Their form also favors the 
same intention. They are thicker before than behind; so 
that, when we stoop forward, the compressible substance of 
the cartilage, yielding in its thicker and anterior part to the 
force which squeezes it, brings the surfaces of the adjoining 
vertebrae nearer to the being parallel with one another than 
they were before, instead of increasing the inclination of 
their planes, which must have occasioned a fissure or open¬ 
ing between them. Thirdly, for the medullary canal giv¬ 
ing out in its course, and in a convenient order, a supply 
of nerves to different parts of the body, notches are made 
in the upper and lower edge of every vertebra, two on 
each edge, equi-distant on each side from the middle line 
of the back. When the vertebras are put together, these 
notches, exactly fitting, form small holes, through which 
the nerves, at each articulation, issue out in pairs, in order 
to send their branches to every part of the body, and with 
an equal bounty to both sides of the body. The fourth 
purpose assigned to the same instrument is the insertion 
of the bases of the muscles, and the support of the ends 
of the ribs; and for this fourth purpose, especially the for 
mer part of it, a figure, specifically suited to the design, 
and unnecessary for the other purposes, is given to the 
constituent bones. Whilst they are plain, and round, and 
smooth, towards the front, where any roughness or projec 
tion might have wounded the adjacent viscera, they run 
out behind, and on each side, into long processes, to which 
processes the muscles necessary to the motions of the trunk 
are fixed; and fixed with such art, that, whilst the verte¬ 
brae supply a basis for the muscles, the muscles help to 
keep these bones in their position, or by their tendons to 
tie them together. 
That most important, however, and general property, viz. 
the strength of the compages, and the security againt lux¬ 
ation, was to be still more specially consulted: for where 
so many joints were concerned, and where, in every one, 
derangement would have been fatal, it became a subject of 
studious precaution. For this purpose, the vertebrae are 
articulated, that is, the moveable joints between them are 
formed by means of those projections of their substance, 
which we have mentioned under the name of processes; 
and these so lock in with, and overwrap one another, as 
