a he thorax, or chest, is composed of bones and cartilages. It is designed not only to protect the heart and lungs, which it contains, but also to allow the whole mass to be turned and twisted with the different movements of the body. This cage is formed, at the back, by the spinal column, on the sides by the ribs, and in front by the breastbone. It protects the heart and lungs as a baseball mask protects the face; its structure is yielding and elastic, so that it may serve as a bellows. The ribs are not complete circles, nor do they parallel each other; they incline downward from the spine and bend at an angle at
The pelvis is the mechanical axis of the body. It is the fulcrum for trunk and legs, and is large in proportion. Its mass inclines a little forward and as compared with the trunk above is somewhat square. The ridge at the sides is called the iliac crest and this is the fulcrum for the lateral muscles; it flares out widely for this purpose, rather more widely in front than behind.
the sides, to take a forward thrust toward the breastbone. The breastbone is called the sternum.
If each rib were rigid and circular, the chest would be immovable and no chest expansion could take place. According to Keill, the breastbone, with an easy inspiration, is thrust out one-tenth of an inch, allowing forty-two cubic inches of air to enter the lungs; and this may be increased, with effort, to seventy or even one hundred cubic inches.
1 he masses of the torso are the chest, the abdomen or pelvis, and between them the epigastrium; the first two comparatively stable, the middle one quite movable.
A straight line marking the collar bones defines the top of the first mass; and paralleling it, a line through the base of the breast muscles and pit of the epigastrium forms its base.
Below this arch is the abdomen, the most movable part of the mobile portion. It is bounded below by a line passing approximately through the anterior points of the iliac crests. Its profile shows the lines of the cone of the thorax diverging downward, the lines of the wedge of the chest and shoulders converging downward, and the buttressing of the lateral muscles.
In the bending or turning of the body the central line of this portion bends always to the convex side, always paralleled by the borders of the rectus muscle.
By this movement the straight wedge of the front is broken. It becomes not a bent wedge, but two wedges; one the upper half of the original wedge, prolonged but not completed downward; the other the lower half, prolonged upward to meet the one above.
More unchanging than either of the above is the mass of the abdomen. The central groove is here shallow and may lose itself below. The long wedge ends in the symphysis pubis.
From the front, the masses of the trunk may be divided into three distinct planes.
The first may be outlined by drawing lines from the inner third of each collar bone to the base of the breast muscles (the point where they take an upward direction to their insertion on the upper arm) and then joining them with a base line across the sixth ribs.
The second is the epigastrium which forms the upper part of the abdominal region. For our purpose, it is a flattened plane bordering the breast muscles above and the stomach below.
The third plane is more rounded and is bounded at the sides by the lower ribs and pelvic bones. It is placed in the lower cavity of the trunk —the abdomen.
MUSCLES OF THE TORSO
1 Pectoralis: pertaining to the breast
2 The serrati: the deep muscles of the spine
3 Muscles that pull the arm down; pectoralis; latissimus dorsi
4 Abductors: draw the thigh toward the medium line
5 Tendons that pass through a loop or slit: omo-hyoid; digastric
6 Pulley: knee-cap, tendon and ligament
7 Rectus, upright: abdominis and femoris
8 Rhomboideus: rhomb-shaped, not right-angled; from the shoulder blade to the spine
9 Deltoid: delta-shaped, triangular, equilateral of the shoulder
10 Trapezius: table-shaped
11 Oblique, slanting
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