east-bone, in a child is composed of six pieces, in
the adult of three, which in old age are consolidated into one bone. The
_Ribs_ are thin, curved bones, being convex externally. There are twelve
on each side, and all are attached to the spinal column. The seven upper
ribs, which are united in front of the sternum, are termed _true_ ribs;
the next three, which are not attached to the sternum, but to one
another are called _false_ ribs; and the last two, which are joined only
to the vertebrae, are designated as _floating_ ribs. The first rib is the
shortest, and they increase in length as far as the eighth, after which
this order is reversed.

[Illustration: Fig. 13.
_1_. The cartilaginous substance
which connects the bodies of
the vertebrae. _2_. The body of the
vertebra. _3_. The spinous process.
_4,4_. The transverse processes.
_5,5_. The articular processes.
_6,6_. A portion of the bony bridge
which assists in forming the spinal
canal (7).]

[Illustration: Fig. 14.
Backbone, spinal
column, or vertebral
column. All
animals possessing
such a row of bones
are called _vertebrates_.
Above _b_ are
the cervical (neck)
vertebrae; _b_ to _c_,
dorsal (back) or
chest vertebrae; _c_
to _d_, lumbar (loins)
vertebrae; _d_ to _e_, sacrum;
_e_ to _f_, coccyx.]

The _Spinal Column_ or backbone, when viewed from the front presents a
perpendicular appearance, but a side view shows four distinct curves.
The bones composing it are called _vertebrae_. The body part of a
vertebra is light and spongy in texture, having seven projections called
_processes_, four of which are the _articular_ processes, which furnish
surfaces to join the different vertebrae of the spinal column. Two are
called _transverse_, and the remaining one is termed the _spinous_. The
transverse and spinous processes serve for the attachment of the muscles
belonging to the back. All these processes are more compact than the
body of the vertebra, and, when naturally connected, are so arranged as
to form a tube which contains the _medulla spinalis_, or spinal cord.
Between the vertebrae is a highly-elastic, cartilaginous and cushion-like
substance, which freely admits of motion, and allows the spine to bend
as occasion requires. The natural curvatures of the spinal column
diminish the shock produced by falling, running or leaping, which would
otherwise be more directly transmitted to the brain. The ribs at the
sides, the sternum in front, and the twelve