Part 7

47. =Reflection of pleura.=--The reflection of the pleura from the wall of the chest on to the diaphragm corresponds with a sloping line drawn from the bottom of the sternum over the cartilages of the ribs down to the lower border of the last rib.

Since the pleura lines the inside of the last rib, a musket ball or other foreign body, loose in the pleural sac, and rolling on the diaphragm, might fall to the lowest part of the sac, which would be between the eleventh and twelfth ribs. The ball might be extracted here. The chest might also be tapped here, but not with a trochar, since a trochar would penetrate both layers of pleura, and go through the diaphragm into the abdomen.

The operation should be done cautiously, by an incision beginning about two inches from the spine, on the outer border of the ‘erector spinæ,’ on a level between the spines of the eleventh and twelfth dorsal vertebræ. The intercostal artery will not be injured if the opening be made below the middle of the space, which is very wide.

THE BACK.

48. =Median furrow.=--In a muscular man, a furrow, caused by the prominence of the erector spinæ on each side, runs down the middle of the back. The lower end of the furrow corresponds with the interval between the spine of the last lumbar and that of the first sacral vertebra.

49. =Spines of vertebræ.=--A little friction with the fingers down the backbone will cause the spines of the vertebræ to be tipped with red, so that they can be easily counted, and any deviation from the straight line detected. Still it is worth remembering that the spine of the third dorsal is on a level with the commencement of the spine of the scapula--that the spine of the seventh dorsal is on a level with the inferior angle of the scapula--that the spine of the last dorsal is on a level with the head of the last rib.

=Division of the trachea.=--The division of the trachea is opposite the spine of the third, in some cases the fourth, dorsal vertebra. In front this division is on the level of the junction of the first with the second bone of the sternum.

The root of the spine of the scapula is marked by a slight dimple in the skin. This is on a level with the third intercostal space. A stethoscope placed on the inner side of this dimple would cover the bronchus, more especially the right, since it is nearer to the chest wall.

Make a man lean forwards, with his arms folded across the chest; this will make prominent the spines of the vertebræ. The lower border of the trapezius will guide you to the spine of the twelfth dorsal vertebra.

50. The place where the kidney is most accessible to pressure is below the last rib, on the outer edge of the erector spinæ.

51. The highest part of the ilium is about the level of the fourth lumbar spine. The best incision for opening the descending colon is in a slightly sloping line beginning at the outer edge of the erector spinæ, midway between the crest of the ilium and the last rib, and continued across the flank for three inches or more, according to the amount of subcutaneous fat.

52. In the pit of the neck we can feel the trapezius and the ligamentum nuchæ. By pressing deeply we detect the forked and prominent spine of the second cervical vertebra.

53. The spines of the third, fourth, and fifth cervical vertebræ recede from the surface to permit free extension of the neck, and cannot often be felt. But the spines of the sixth and seventh (v. prominens) stand out well.

54. Notice that most of the spines of the dorsal vertebræ, owing to their obliquity, do not tally with the heads of their corresponding ribs. Thus, the spine of the second dorsal corresponds with the head of the third rib; the spine of the third dorsal with the head of the fourth rib, and so on till we come to the eleventh and twelfth dorsal vertebræ, which do tally with their corresponding ribs. All this, however, is best seen in the skeleton.

55. The spines of the vertebræ may be useful as landmarks indicative of the levels of important organs. I have therefore arranged them in a tabular form, thus:--

TABULAR PLAN OF PARTS OPPOSITE THE SPINES OF THE VERTEBRÆ.

{ 5th. Cricoid cartilage. Œsophagus begins. CERVICAL. { 7th. Apex of lung: higher in the female than in the { male. (30)

{ 1st. { 2nd. { 3rd. Aorta reaches spine. Apex of lower lobe of lung. { Angle of bifurcation of trachea. (49) { 4th. Aortic arch ends. Upper level of heart. { 5th. { 6th. DORSAL. { 7th. { 8th. Lower level of heart. Central tendon of diaphragm. { 9th. Œsophagus and vena cava through diaphragm. Upper edge of spleen. { 10th. Lower edge of lung. Liver comes to surface posteriorly. Cardiac orifice of stomach. { 11th. Lower border of spleen. Renal capsule. { 12th. Lowest part of pleura. Aorta through diaphragm. Pylorus.

{ 1st. Renal arteries. Pelvis of kidney. (83) { 2nd. Termination of spinal cord. Pancreas. Duodenum just below. Receptaculum chyli. LUMBAR. { 3rd. Umbilicus. Lower border of kidney. { 4th. Division of aorta. (65) Highest part of ilium. { 5th.

56. =Origins of the spinal nerves.=--It is useful to know opposite what vertebræ the spinal nerves in the different regions arise from the spinal cord. They arise as follows:--

The origins of the eight cervical nerves correspond to the interval between the occiput and the sixth cervical spine.

The origins of the first six dorsal nerves correspond to the interval between the sixth cervical and the fourth dorsal spines.

The origins of the six lower dorsal nerves correspond to the interval between the fourth and the eleventh dorsal spines.

The origins of the five lumbar nerves correspond to the interval between the eleventh and twelfth dorsal spines.

The origins of the five sacral nerves correspond to the spines of the last dorsal and the first lumbar vertebræ.

57. =Movements of the spine.=--The movements of which the spine is capable are threefold: 1. Flexion and extension; 2. Lateral inclination; 3. Torsion. Flexion and extension are freest between the third and the sixth cervical vertebræ, between the eleventh dorsal and the second lumbar, and between the last lumbar and the sacrum. This is well marked in severe cases of opisthotonos, where the body is supported on the back of the head and heels.

Still better may it be observed when a mountebank bends backwards, and touches the ground with his head.

The lateral movement is freest in the neck and the loins.