g. To
produce these effects they all act together. Their violent and
continued action sometimes produces hernia, and, when spasmodic, may
occasion ruptures of the different organs.

2d. The contraction and relaxation of the abdominal muscles and
diaphragm stimulate the stomach, liver, and intestines to a healthy
action, and are subservient to the digestive powers. If the
contractility of their muscular fibres is destroyed or impaired, the
tone of the digestive apparatus will be diminished, as in indigestion
and costiveness. This is frequently attended by a displacement of
those organs, as they generally gravitate towards the lower portion of
the abdominal cavity, when the sustaining muscles lose their tone and
become relaxed.

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What causes the hollow eye and sunken cheek after a severe sickness?
158. How many muscles in the human system? Into how many layers are
they arranged? What is a voluntary muscle? Give examples. What is an
involuntary muscle? Mention examples. Give observation 1st, respecting
the use of the abdominal muscles? Observation 2d.

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[Illustration: Fig. 39. A front view of the muscles of the trunk. On the
left side the superficial layer is seen; on the right, the deep layer. 1,
The pectoralis major muscle. 2, The deltoid muscle. 6, The pectoralis
minor muscle. 9, The coracoid process of the scapula. 11, The external
intercostal muscle. 12, The external oblique muscle 13, Its aponeurosis.
16, The rectus muscle of the right side. 18, The internal oblique muscle.

_Practical Explanation._ The muscle 1 draws the arm by the side, and
across the chest, and likewise draws the scapula forward. The muscle 2
elevates the arm. The muscle 6 elevates the ribs when the scapula is
fixed, or draws the scapula forward and downward when the ribs are fixed.
The muscles 12, 16, 18, bend the body forward or elevate the hips when
the muscles of both sides act. They likewise depress the rib in
expiration. When the muscles on only one side act, the body is twisted to
the same side.]

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Explain fig. 39. Give the function of some of the most prominent
muscles, from this figure.

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[Illustration: Fig. 40. A lateral view of the muscles of the trunk. 3,
The upper part of the external oblique muscle. 4, Two of the external
intercostal muscles. 5, Two of the internal intercostals. 6, The
transversalis muscle. 7, Its