e thorax in relation to that of the abdomen
varies in the individual at different periods of life. At an early age,
the thorax, compared to the abdomen, is less in proportion than it is at
adult age. The digestive organs in early age preponderate considerably
over the respiratory organs; whereas, on the contrary, in the healthy
and well-formed adult, the thoracic cavity and organs of respiration
manifest a greater relative proportion to the ventral cavity and organs.
At the adult age, when sexual peculiarities have become fully marked,
the thoracic organs of the male body predominate over those of the
abdomen, whilst in the female form the ventral organs take precedence as
to development and proportions. This diversity in the relative capacity
of the thorax and abdomen at different stages of development, and also
in persons of different sexes, stamps each individual with
characteristic traits of physical conformation; and it is required that
we should take into our consideration this normal diversity of
character, while conducting our examinations of individuals in reference
to the existence of disease.

The heart varies in some measure, not only as to size and weight, but
also as to position, even in healthy individuals of the same age and
sex. The level at which the heart is in general found to be situated in
the thorax is that represented in PLATE 23, where the apex points to the
sixth intercostal space on the left side above K, while the arch of the
aorta rises to a level with C, the second costal cartilage. In some
instances, the heart may be found to occupy a much lower position in the
thorax than the one above mentioned, or even a much higher level. The
impulse of the right ventricle, F, has been noticed occasionally as
corresponding to a point somewhat above the middle of the sternum and
the intercostal space between the fourth and fifth left costal
cartilages; while in other instances its beating was observable as low
down as an inch or more below the xiphoid cartilage, and these
variations have existed in a state of health.

Percussion over the region of the heart yields a dull flat sound. The
sound is dullest opposite the right ventricle, F; whilst above and to
either side of this point, where the heart is overlapped by the anterior
shelving edges of both lungs, the sound is modified in consequence of
the lung's resonant qualities. The heart-sounds, as heard through the
stethoscope, in valvular disease, will