59. The sliding movement of the scapula on the chest can be properly understood only on the living subject. It can move not only upwards and downwards as in shrugging the shoulders—backwards and forwards as in throwing back the shoulders—but it has a rotatory movement round a movable centre. This rotation is seen while the arm is being raised from the horizontal to the vertical position, and is effected by the co-operation of the trapezius with the serratus magnus. The glenoid cavity is thus made to look upwards, the inferior angle slides forwards, and is well held under the latissimus dorsi.
60. For the medical examination of the back, the patient should sit with the arms hanging between his thighs, to lower the scapulæ as much as possible. In this position the spine of the scapula corresponds (nearly) with the fissure between the upper and lower lobes of the lung; the apex of the lower lobe being about the level of the third rib.
THE ABDOMEN.
The student is assumed to be familiar with the conventional lines dividing the abdomen into regions.
61. Abdominal lines.—The linea alba, or central line of the abdomen, marks the union of the aponeuroses of the abdominal muscles. It runs from the apex of the ensiform cartilage to the symphysis pubis. As this line is the thinnest and least vascular part of the abdominal wall, we make our incision along it in ovariotomy, and in the high operation of lithotomy; in it, we tap the abdomen in ascites, and the distended bladder in retention of urine.
The so-called ‘linea semilunaris,’ at the outer border of the sheath of the rectus, corresponds with a line, drawn slightly curved (with the concavity towards the linea alba), from the lowest part of the seventh rib to the spine of the pubes. This line would be in an adult about three inches from the umbilicus; but in an abdomen distended by dropsy or other cause, the distance is increased in proportion.
It is important to know the position of the ‘lineæ transversæ,’ or tendinous intersections across the rectus abdominis. There are rarely any below the umbilicus, and generally three above it. The first is about the level of the umbilicus. The second is about four inches higher—that is, about the level of the lowest part of the tenth rib. These are the principal lines, and they divide the upper part of each rectus into two nearly quadrilateral portions, an upper and a lower: of these, those on the right side are a trifle larger than on the left. We see these muscular squares pretty plainly in some athletic subjects. Much more frequently we see them, too much exaggerated, on canvas and in marble. Artists are apt to exaggerate them, and make the front of the belly too much like a chess-board. It is lucky for them that all the world do not see with anatomical eyes.
A familiarity with the shape and position of these divisions of the rectus is of importance, lest we should, in ignorance, make a mistake in our diagnosis. A spasmodic contraction of one of these divisions, particularly the upper, or a collection of matter within its sheath, has been frequently mistaken for deep-seated abdominal disease.
In the erect position, the anterior superior spines of the ilia are a little below the level of the promontory of the sacrum. The bifurcation of the aorta is on about the level of the highest part of the crest of the ilium.
62. Umbilicus.—The umbilicus is not midway between the ensiform cartilage and the pubes, but rather nearer to the pubes. In all cases it is situated above the centre of a man’s height. It is a vulgar error to say that when a man lies with legs and arms outstretched, and a circle is drawn round him, the umbilicus lies in the centre of it. This central point is in most persons just above the pubes.