Part 10 (1/2)

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.]

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

[Ill.u.s.tration: 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 posterior aponeurosis. 8, Its anterior aponeurosis. 11, The right rectus muscle. 13, The crest of the ilium, or haunch-bone.

_Practical Explanation._ The rectus muscle, 11, bends the thorax upon the abdomen when the lower extremity of the muscle is the fixed point; but when the upper extremity is the fixed point, the effect is to bring forward and raise the pelvis and lower extremities. They likewise depress the ribs in respiration. The transverse muscle, 6, 7, 8, lessens the cavity of the abdomen, and presses the intestines; stomach, and liver upward, against the diaphragm, in expiration.]

3d. The region of the back, in consequence of its extent, is common to the neck, the upper extremities, and the abdomen. The muscles of which it is composed are numerous, and are arranged in six layers.

What is represented by fig. 40? Give the function of some of the muscles represented by this figure.

[Ill.u.s.tration: Fig. 41 The first, second, and part of the third layer of muscles of the back. The first layer is shown on the right, and the second on the left side. 1, The trapezius muscle. 2, The spinous processes of the vertebr. 3, The acromion process and spine of the scapula. 4, The latissimus dorsi muscle. 5, The deltoid muscle. 7, The external oblique muscle. 8, The gluteus medius muscle. 9, The gluteus maximus muscle, 11, 12, The rhomboideus major and minor muscles. 15, The vertebral aponeurosis. 16, The serratus posticus inferior muscle. 22, The serratus magnus muscle. 23, The internal oblique muscle.

_Practical Explanation._ The muscles 1, 11, 12, draw the scapula back toward the spine. The muscles 11, 12, draw the scapula upward toward the head, and slightly backward. The muscle 4 draws the arm by the side, and backward, The muscle 5 elevates the arm. The muscles 8, 9, extend the thigh on the body. The muscle 1 draws the head back and elevates the chin. The muscle 16 depresses the ribs in expiration. The muscle 22 elevates the ribs in inspiration.]

159. The diaphragm, or midriff, is the muscular division between the thorax and the abdomen. It is penetrated by the oesophagus on its way to the stomach, by the aorta conveying blood toward the lower extremity, and by the ascending vena cava, or vein, on its way to the heart.

[Ill.u.s.tration: Fig. 42. A representation of the under, or abdominal side of the diaphragm. 1, 2, 3, 4, The portion which is attached to the margin of the ribs. 8, 10, The two fleshy pillars of the diaphragm, which are attached to the third and fourth lumbar vertebr. 9, The spinal column.

11, The opening for the pa.s.sage of the aorta. 12, The opening for the oesophagus. 13, The opening for the ascending vena cava, or vein.]

_Observation._ The diaphragm may be compared to an inverted basin, its bottom being turned upward into the thorax, while its edge corresponds with the outline of the edges of the lower ribs and sternum. Its concavity is directed toward the abdomen, and thus, this cavity is very much enlarged at the expense of that of the chest, which is diminished to an equal extent.

159. Describe the diaphragm. What vessels penetrate this muscular septum?

160. ”The motions of the fingers do not merely result from the action of the large muscles which lie on the fore-arm, these being concerned more especially in the stronger actions of the hands. The finer and more delicate movements of the fingers are performed by small muscles situated in the palm and between the bones of the hand, and by which the fingers are expanded and moved in all directions with wonderful rapidity.”

[Ill.u.s.tration: Fig. 43. A front view of the superficial layer of muscles of the fore-arm. 5, The flexor carpi radialis muscle. 6, The palmaris longus muscle. 7, One of the fasciculi of the flexor sublimis digitorum muscle, (the rest of the muscle is seen beneath the tendons of the pintails longus.) 8, The flexor carpi ulnaris muscle. 9, The palmar fascia. 11, The abductor pollicis muscle. 12, One portion of the flexor orevis pollicis muscle. 13, The supinator longus muscle. 14, The extensor ossis metacarpi, and extensor primi internodii pollicis muscles, curving around the lower border of the fore-arm. 15, The anterior portion of the annular ligament, which binds the tendons in their places.

_Practical Explanation._ The muscles 5, 6, 8, bend the wrist on the bones of the fore-arm. The muscle 7 bends the second range of finger-bones on the first. The muscle 11 draws the thumb from the fingers. The muscle 12 flexes the thumb. The muscle 13 turns the palm of the hand upward. The muscles 8, 13, 14, move the hand laterally.]

[Ill.u.s.tration: Fig. 44. A back view of the superficial layer of muscles of the fore-arm. 5, The extensor carpi radialis longior muscle. 6, The extensor carpi radialis brevior muscle. 7, The tendons of insertion of these two muscles. 8, The extensor communis digitorum muscle. 9, The extensor minimi dlgiti muscle. 10, The extensor carpi ulnaris muscle. 13, The extensor ossis metacarpi and extensor primi internodii muscles, lying together. 14, The extensor secundi internodii muscle; its tendon is seen crossing the two tendons of the extensor carpi radialis longior and brevior muscles. 15, The posterior annular ligament. The tendons of the common extensor muscle of the fingers are seen on the back of the hand, and their mode of distribution on the back of the fingers.

_Practical Explanation._ The muscles 5, 6, 10, extend the wrist on the fore-arm. The muscle 8 extends the fingers. The muscle 9 extends the little finger. The muscles 13 extend the metacarpal bone of the thumb, and its first phalanx. The muscle 14 extends the last bone of the thumb.

The muscles 10, 13, 14, move the hand laterally.]

160. Where are the muscles situated that effect the larger movements of the hand? That perform the delicate movements of the fingers? Give the use of some of the muscles represented by fig. 43. Those represented by fig. 44.

CHAPTER IX.