y. 5, The transverse process. 7, The inferior articulating
process. 8, The superior articulating process.]

[Illustration: Fig. 11. 1, The cartilaginous substance that connects the
bodies of the vertebrae. 2, The body of the vertebra. 3, The spinous
process. 4, 4, The transverse processes. 5, 5, The articulating
processes. 6, 6, A portion of the bony bridge that assists in forming the
spinal canal, (7.)]

_Observation._ A good idea of the structure of the vertebrae may be
obtained by examining the spinal column of a domestic animal, as the
dog, cat, or pig.

91. The PELVIS is composed of four bones; the two _in-nom-i-na'ta_,
(nameless bones,) the _sa'crum_, and the _coc'cyx_.

92. The INNOMINATUM, in the child, consists of three pieces. These,
in the adult, become united, and constitute but one bone. In the sides
of these bones is a deep socket, or depression, like a cup, called the
_ac-e-tab'u-lum_, in which the round head of the thigh-bone is
placed.

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90. What is said of the curves of the spinal column? What is
represented by fig. 10? By fig. 11? How can the structure of the
vertebrae be seen? 91. Of how many bones is the pelvis composed? 92.
What is said of the innominatum in the child?

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93. The SACRUM, so called because the ancients offered it in
sacrifices, is a wedge-shaped bone, that is placed between the
innominata, and to which it is bound by ligaments. Upon its upper
surface it connects with the lower vertebra. At its inferior, or lower
angle, it is united to the coccyx. It is concave upon its anterior,
and convex upon its posterior surface.

[Illustration: Fig. 12. 1, 1, The innominata, (nameless bones.) 2, The
sacrum. 3, The coccyx. 4, 4, The acetabulum. a, a, The pubic portion of
the innominata. d, The arch of the pubes; e, The junction of the sacrum
and lower lumbar vertebra.]

94. The COCCYX, in infants, consists of several pieces, which, in
youth, become united and form one bone. This is the terminal extremity
of the spinal column.

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In the adult? Describe the acetabulum. 93. Describe the sacrum.
Explain fig. 12. 94. Describe the coccyx.

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CHAPTER V.

ANATOMY OF THE BONES, CONTINUED

95. The bones of the upper and lower limbs are enlarged at each
extremity, and have projections, or processes. To these, the tendons
of muscles and ligaments are attached, which connect