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sound on percussion, whilst, by the ear or stethoscope applied to a
corresponding part of the thoracic walls, we discover the absence of the
respiratory murmur.

The transverse diameter of the thoracic cavity varies at different
levels from above downwards. The diameter which the two first ribs, B
B*, measure, is the least. That which is measured by the two eighth
ribs, I I*, is the greatest. The perpendicular depth of the thorax,
measured anteriorly, ranges from A, the top of the sternum, to F, the
xyphoid cartilage. Posteriorly, the perpendicular range of the thoracic
cavity measures from the spinous process of the seventh cervical
vertebra above, to the last dorsal spinous process below. In full,
deep-drawn inspiration in the healthy adult, the ear applied to the
thoracic walls discovers the respiratory murmur over all the space
included within the above mentioned bounds. After extreme expiration, if
the thoracic walls be percussed, this capacity will be found much
diminished; and the extreme limits of the thoracic space, which during
full inspiration yielded a clear sound, indicative of the presence of
the lung, will now, on percussion, manifest a dull sound, in consequence
of the absence of the lung, which has receded from the place previously
occupied.

Owing to the conical form of the thoracic space, the apex of which is
measured by the first ribs, B B*, and the basis by I I*, it will be seen
that if percussion be made directly from before, backwards, over the
pectoral masses, R R*, the pulmonic resonance will not be elicited. When
we raise the arms from the side and percuss the thorax between the folds
of the axillae, where the serratus magnus muscle alone intervenes
between the ribs and the skin, the pulmonic sound will answer clearly.

At the hypochondriac angles formed between the points F, L, N, on either
side the lungs are absent both in inspiration and expiration.
Percussion, when made over the surface of the angle of the right side,
discovers the presence of the liver, G G*. When made over the median
line, and on either side of it above the umbilicus, N, we ascertain the
presence of the stomach, M M*. In the left hypochondriac angle, the
stomach may also be found to occupy this place wholly.

Beneath the umbilicus, N, and on either side of it as far outwards as
the lower asternal ribs, K L, thus ranging the abdominal parietes
transversely, percussion discovers the transverse colon, O, P, O*. The
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