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CHAPTER III. 
OF THE BONES OF THE TRUNK. 
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HE bones of the trunk are thofe which compofe the 
lpine or chain of bones from the head down to the 
rump, the ribs and fternum, to which may juftly be 
added the ofla innominata. 
The fpine, is compofed of twenty four vertebra, 
(each of which in a young child is three bones) befides 
thofe of the os facrum and coccygis; feven belong to the neck, the firft of 
which is called atlas, becaufe it immediately fupports the head; its upper 
fide has two cavities, into which the apophyfes of the os occipitisare re¬ 
ceived, but thefe two cavities together, unlike all other joints, are lateral- 
ly portions of concentric circles, by which means they are but as one 
joint, and fo fuffer the head to move eafily fide-ways, which otherwife 
it could no more do than the knee, which alfo has two heads and two 
cavities. The under fide of this bone has a very flat articulation with the 
next, which fits it for a rotatory motion. The fecond vertebra is called 
dcntata, or axis, from a procefs which paffes through the former bone, 
and is the axis upon which it turns; nevertheless all the vertebra of the 
neck contribute fomething to the rotatory motion of the head. The pro- 
ceflus dentatus is ftrongly tied to the os occipitis, and to the atlas by li- 
