united to the sternum, through the medium
of cartilages, and are called the _true ribs_. The cartilages of the
next three are united with each other, and are not attached to the
sternum; these are called _false ribs_. The lowest two are called
_floating ribs_, as they are not connected either with the sternum or
the other ribs.

87. The SPINAL COLUMN is composed of twenty-four pieces of bone. Each
piece is called a _vert'e-bra_. On examining one of the bones, we find
seven projections, called _processes_; four of these, that are
employed in binding the bones together, are called _articulating_
processes; two of the remaining are called the _transverse_; and the
other, the _spinous_. The last three give attachment to the muscles of
the back.

88. The large part of the vertebra, called the body, is round and
spongy in its texture, like the extremity of the round bones. The
processes are of a more dense character. The projections are so
arranged that a tube, or canal, is formed immediately behind the
bodies of the vertebrae, in which is placed the _me-dul'la spi-na'lis_,
(spinal cord,) sometimes called the pith of the back-bone.

89. Between these joints, or vertebrae, is a peculiar and highly
elastic substance, which much facilitates the bending movements of the
back. This compressible cushion of cartilage also serves the important
purpose of diffusing and diminishing the shock in walking, running, or
leaping, and tends to protect the delicate texture of the brain.

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86. How are the ribs united to the sternum? 87. Describe the spinal
column. 88. Give the structure of the vertebra. Where is the spinal
cord placed? 89. What is placed between each vertebra? What is its
use?

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90. Another provision for the protection of the brain, which bears
convincing proof of the wisdom and beneficence of the Creator, is the
antero-posterior, or forward and backward curve of the spinal column.
Were it a straight column, standing perpendicularly, the slightest
jar, in walking, would cause it to recoil with a sudden jerk; because,
the weight bearing equally, the spine would neither yield to the one
side nor the other. But, shaped as it is, we find it yielding in the
direction of the curves, and thus the force of the shock is diffused.

[Illustration: Fig. 10. A vertebra of the neck. 1, The body of the
vertebra. 2, The spinal canal. 4, The spinous process, cleft at its
extremit