ore they can be adapted to the wants of the body?
By what organs are these changes effected? 464-474. _Give the anatomy
of the respiratory organs._ 464. Name the respiratory organs. What
organs also aid in the respiratory process? 465. Describe the lungs.

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[Illustration: Fig. 89. A back view of the heart and lungs. The posterior
walls of the chest are removed. 1, 2, 3, The upper, middle, and lower
lobes of the right lung. 8, 9, 10, The two lobes of the left lung. 6, 13,
The diaphragm. 7, 7, 14, 14, The pleura that lines the ribs. 4, 11, The
pleura that lines the mediastine. 5, 12, 12, The portion of the pleura
that covers the diaphragm. 15, The trachea, 16, The larynx. 19, 19, The
right and left bronchia. 20, The heart. 29, The lower part of the spinal
column.]

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Explain fig. 89.

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466. Each lung is enclosed, and its structure maintained by a serous
membrane, called the _pleu'ra_, which invests it as far as the root,
and is thence reflected upon the walls of the chest. The lungs,
however, are on the outside of the pleura, in the same way as the head
is on the outside of a cap doubled upon itself. The reflected pleurae
in the middle of the thorax form a partition, which divides the chest
into two cavities. This partition is called the _me-di-as-ti'num_.

[Illustration: Fig. 90. The heart and lungs removed from the chest, and
the lungs freed from all other attachments. 1, The right auricle of the
heart. 2, The superior vena cava. 3, The inferior vena cava. 4, The right
ventricle. 5, The pulmonary artery issuing from it. _a_, _a_, The
pulmonary artery, (right and left,) entering the lungs. _b_, _b_,
Bronchia, or air-tubes, entering the lungs. _v_, _v_, Pulmonary veins,
issuing from the lungs. 6, The left auricle. 7, The left ventricle. 8,
The aorta. 9, The upper lobe of the left lung. 10, Its lower lobe. 11,
The upper lobe of the right lung. 12, The middle lobe. 13, The lower
lobe.]

_Observation._ When this membrane that covers the lungs, and also
lines the chest, is inflamed, the disease is called "pleurisy."

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466. By what are the lungs enclosed? What is the relative position of
the lungs and pleura? What is said of the reflected pleurae? Explain
fig. 90. What part of the lungs is affected in pleurisy?

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467. The lungs are composed of the ramifications of the bronchial
t