surface. It aids materially in
the circulation of the fluids, in opposition to the laws of gravity.
In the palm of the hand and sole of the foot, it is a powerful
protection to the structures that enter into the formation of these
parts. In all parts of the system, the separate muscles are not only
invested by fascia, but they are arranged in layers, one over
another. The sheath of each muscle is loosely connected with another,
by the cellular membrane.

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153. What is meant by the origin of a muscle? The insertion? The
swell? What is the color of muscles? With what is each muscular fibre
supplied? 154. What is said of fascia? What is its appearance when
freshly exposed? 155. What effect has it on the muscles? Give other
uses of the fascia.

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156. The interstices between the different muscles are filled with
adipose matter, or fat. This is sometimes called the packing of the
system. To the presence of this tissue, youth are indebted for the
roundness and beauty of their limbs.

[Illustration: Fig. 37. A transverse section of the neck. The separate
muscles, as they are arranged in layers, with their investing fasciae, are
beautifully represented. As the system is symmetrical, figures are placed
only on one side. In the trunk the muscles are arranged in layers,
surrounded by fasciae, as in the neck. The same is true of the muscles of
the upper and lower limbs.

12, The trachea, (windpipe.) 13, The oesophagus, (gullet.) 14, The
carotid artery and jugular vein. 28, One of the bones of the spinal
column. The figures that are placed in the white spaces represent some of
the fasciae; the other figures indicate muscles.]

157. The muscles may be arranged, in conformity with the general
division of the body, into four parts: 1st. Those of the _Head_
and _Neck_. 2d. Those of the _Trunk_. 3d. Those of the _Upper
Extremities_. 4th. Those of the _Lower Extremities_.

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156. Give a reason why the limbs of youth are rounder than those of
the aged. Describe fig. 37.

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[Illustration: Fig. 38. The superficial layer of muscles on the face and
neck. 1, 1, The occipito-frontalis muscle. 2, The orbicularis
palpebrarum. 6, The levator labii superioris 7, The levator anguli oris.
8, The zygomaticus minor. 9, The zygomaticus major 10, The masseter. 11,
The depressor labii superioris. 13, The orbicularis oris. 15, The
depress