CHAPTER III. 
gaments, to prevent its hurting the fpinal marrow. Twelve of which 
belong to the back, five to the loins. The os facrum is fometimes five, 
fometimes fix bones, and the os coccigis four. If this chain had been 
compolcd of fewer bones, they mull have either not been capable of 
bending fo much as they do, or have bent more in each joint, which 
would have prefled the fpinal marrow, the ill confequences of which 
are fufficiently feen in perfons grown crooked, or who have had diftor- 
tions from external accidents. 
The uppermoft vertebra of the neck, being fixed behind the center of 
gravity of the head, the neck is therefore fo far bent forward, as that the 
iaft of thefe vertebra (which has a firm bearing upon thofe of the tho¬ 
rax) may be exactly under the center of gravity. Thofe of the thorax are 
bent backwards, behind the center of motion, to make room for the 
parts contained in the thorax, and that they might not be made too weak 
by this ftructure, they are formed for lefs motion than other vertebra; and 
thofe in particular, who are bent fartheft from the center of gravity have 
the leaft motion. The middle vertebra of the loins, are again bent for¬ 
wards under the center of gravity, or near it; and from thence they go 
backwards to the os facrum, where being fixed to the ofla innominata 
behind the center of gravity, the articulation is therefore firm and with¬ 
out motion, and from thence the ofla innominata are fo formed, as that 
their lockets into which the thigh bones are fixed, where there is a free 
motion, are exa&ly under the center of gravity. In brutes the fpine is 
differently formed, according to the actions for which they are defigned. 
(See chapter x.) 
In all thefe vertebra, except the firfl, is a middle anterior fpongy body, 
by which they are firmly articulated with a very flrong intervening liga¬ 
ment ; and from the middle of the hind part of each, except the firfl. 
Hands a procefs named fpinal is, and from every one a procefs on each fide, 
called tranfverfalis, and two fuperior, and two inferior fhort ones; by 
which the back parts of the vertebra are articulated, named obliqui, fu- 
periores, and inferiores. 
The fore part of the 1even vertebra of the neck, and two upper of the 
back, arc flat forwards, to make room for the afperaarteria and gula: The 
third and fourth of the back acute, to give way to the veflels of the lungs 
and heart, and bent to the right fide for the better fituation of the heart, 
which makes that fide of the breaft more convex than the other, and 
therefore ftrongcr; which feems advantageous to the right arm, its mo¬ 
tions depending upon the fupport it receives from the breaft. 
