thyrohyoid ligaments, and the lower, which are shorter
and thicker, present internally a facet for articulation
with the cricoid cartilage.
Sagittal section of larynx, right half.
The cricoid cartilage resembles a signet ring, is
narrow in front, and gives attachment to the crico-
thyroid muscle, and behind it to some of the fibers
of the inferior constrictor. It is broad behind, with
a vertical ridge for the attachment of the longitudinal
fibers of the esophagus, and presents at about
the middle of the lateral surface a prominence on
each side which articulates with the corresponding
236 THE RESPIRATORY APPARATUS
inferior cornua of the thyroid cartilage. The lower
border is joined to the upper ring of the trachea; the
upper border gives attachment in front and laterally
to the cricothyroid membrane and the lateral crico-
arytenoideus muscle. Behind, at each end of its upper
border, is an oval surface for the corresponding ary-
tenoid cartilage, with a notch between. The inner
surface is smooth and lined with mucous membrane.
The arytenoid cartilages are pyramidal in form,
presenting three surfaces, an apex, and base, and
rest by their bases on the highest part of the upper
border of the cricoid cartilage behind, their curved
The cornicula laryngis (cartilages of Santorini) are two
small, cervical nodules of yellow elastic tissue, which
articulate with the summits of the arytenoid cartilages
and serve to prolong them backward and inward.
The- cuneiform cartilages (Wrisberg's) are two small,
yellow bodies of elastic cartilage, which stretch between
the arytenoid cartilage and the epiglottis.
The epiglottis is a fibrocartilaginous lamella, shaped
like a leaf, lying behind the tongue and in front of
the upper orifice of the larynx. Above it is broad,
below narrow and prolonged to the notch above the
pomum Adami by the thyro-epiglottic ligament, or
rather, to the angular interval just below the notch,
and is attached to the upper border of the body of the
hyoid bone by the hyo-epiglottic ligament. It falls
downward over the opening of the larynx during the
swallowing of food to prevent the same from entering
The ligaments of the larynx are extrinsic and intrinsic.
The former connect it to the hyoid bone; the latter
connect its parts together.
The extrinsic ligaments, meaning those coming
from without or on the outside of the larynx, are the
middle thyrohyoid ligament, the two lateral thyro-
hyoid ligaments, and the hyo-epiglottic ligament.
THE ORGANS OF RESPIRATION 237
The intrinsic ligaments, meaning those within or
on the inside of the larynx, connecting the thyroid
and cricoid cartilages, are the cricothyroid membrane,
two capsular ligaments.
The cricoid and arytenoid cartilages are connected
by loose capsular ligaments lined by synovial mem-
branes, and by a posterior cricoarytenoid ligament
running from the cricoid to the inner and back part
of the base of the arytenoid.
The Interior of the Larynx (Cavum Laryngis). This
is divided into an upper and a lower part by the rima
glottidis. The upper opens into the pharynx by the
upper aperture of the larynx, between which and the
rima glottidis are the ventricles and their saccules, and
the false vocal cords. The lower aperture is continuous
with the trachea.
The rima glottidis is the space between the true
vocal cords and the bases of the arytenoid cartilages.
It is somewhat less than 1 inch long, and according to
its degree of dilatation, from f to J inch wide. In
easy respiration its form is triangular with the base
posterior, and when fully dilated it is lozenge-shaped.
The superior or false vocal cords are two mucous
folds, each enclosing the corresponding superior
thyro-arytenoid ligament. This latter is a thin band
running between the angle of the thyroid and the
antero-external surface of the arytenoid cartilage.
The inferior or true vocal cords are two strong bands,
the inferior thyro-arytenoid ligaments, covered by
mucous membrane and attached to the depression
between the alse of the thyroid cartilage in front and
the anterior angle of the base (vocal process) of the
arytenoid cartilages behind.
The ventricles of the larynx lie one on each side,
between the upper and lower vocal cords, bounded
externally by the thyro-arytenoidei.
The saccule of the larynx is a space on each side,
between the false vocal cord and the inner surface
238 THE RESPIRATORY APPARATUS
of the thyroid cartilage, reaching upward as high as
the upper border of that cartilage, and its mucous
membrane presents the orifices of sixty or seventy
glands. This space has a fibrous capsule.
The muscles of the larynx are divided into extrinsic
and intrinsic the former will be found under the
muscle system. The latter are:
Crico thyroid. Posterior crico-arytenoid.
Thyro-arytenoid. Lateral crico-arytenoid.
Thyro-epiglotticus. Arytenoid (single).
Actions of the intrinsic muscles: (1) Those which
open and close the glottis. (2) Those which regulate
the degree of tension of the vocal cords.
1. The two posterior crico-arytenoids open the
glottis; and the arytenoid and the two lateral crico-
arytenoids close it.
2. The two cricothyroids regulate the tension of
the vocal cords, and elongate them by the same action;
the two thyro-arytenoids relax and shorten them.
Phonation, Articulate Speech. Phonation is the
phenomenon whereby the animal and human being
are enabled to utter vocal sounds, due to the vibration
of two elastic membranes, the vocal cords, which
cross the opening of the larynx from before backward,
and which are thrown into vibration by the air forced
from the lungs.
Articulate speech is a modification of the vocal
sounds or the voice produced by the teeth and the
muscles of the lips and tongue, and is employed for
the expression of ideas (Brubaker).
The Trachea. The trachea is a membranocar-
tilaginous tube, flattened behind, continuous above
with the larynx, and below dividing into the two
The trachea consists of sixteen to twenty incomplete
cartilaginous rings connected by a fibrous membrane.
THE ORGANS OF RESPIRATION
Their free ends, which are directed posteriorly, are
united similarly and by plain muscular tissue. Its
upper limit is at the sixth cervical, its lower, opposite
the body or upper border of the fifth thoracic vertebra,
Trachea and bronchi, front view. (Testut.)
and it measures about 4J inches in length; transversely,
f to 1 inch. Its inner surface is lined by a mucous
membrane which belongs to the stratified, ciliated
variety of tissues, and this cilia possesses a per-
petual movement, carrying the particles of dust, etc.,
240 THE RESPIRATORY APPARATUS
entangled in the mucus toward the entrance of the
respiratory tract, where it is expectorated. The
submucosa contains numbers of mucous glands.
The Bronchi. The bronchi enter the hilum of the
corresponding lung. The right is the shorter, wider,
and more horizontal, and enters the lung opposite the
fifth thoracic vertebra, the larger azygos vein arching
over it from behind, the right pulmonary artery below
and then in front of it. The left bronchus is about
2 inches long, and enters the lung opposite the sixth
dorsal vertebra. It passes under the arch of the aorta
and crosses in front of the esophagus, thoracic duct,
and descending aorta. The left pulmonary artery
lies at first above, then in front of it.
Their structure resembles the trachea, only that
the cartilaginous rings become thinner and are replaced
by an increase in the muscular coat, as they approach
the terminal bronchioles. The alveoli, the termination
of the bronchioles, rest on a basement membrane of
elastic tissue, surrounded by a capillary plexus formed
by the pulmonary arteries and veins.
The Pleurae. The pleurae are two separate serous
sacs which invest each lung to its root and are reflected
on to the thoracic walls and pericardium. That portion
of the serous membrane investing the surface of the
lung and extending into the fissures between the
lobes is called the visceral layer of the pleura (pleura
pulmonalis), while the portion lining the inner surface
of the thorax is called the parietal layer of the pleura
(pleura parietalis). The latter is subdivided into the
cervical, the costal, the diaphragmatic, and the
mediastinal portions. The space between the visceral
and parietal layers is the pleural cavity (cavum pleurae),
and contains a small amount of clear fluid. There is
no cavity when the pleura? are in a healthy condition,
the two layers being in contact.
The two pleurse are distinct from each other, and
do not meet in the median line except behind the
THE ORGANS OF RESPIRATION
second piece of the sternum. At the root of the lung
the visceral and parietal layer of the same side are
continuous, and at the lower part of the root a fold,
the ligamentum latum pulmonis, runs down to the
Left Phrenic Nerve
Sympathetic JVi . .
Vena Azygos Majc
A transverse section of the thorax, showing the relative positions of the
viscera and the reflections of the pleurae. (Gray.)
The Lungs (Pulmones). The lungs are the essential
organs of respiration; they are situated in the right
and left sides of the thorax, covered by the visceral
portion of the pleura; filling the cavity, with the
exception of the intervening mediastinum. The
latter is a space within the thorax situated between
the right and left lobes of the lungs; it contains the
heart covered by the pericardium, the great vessels
of the heart, the esophagus, trachea, bronchi, thymus
gland, thoracic ducts, nerves to the heart, lungs, and
other organs. It is divided into superior, anterior,
THE RESPIRATORY APPARATUS
middle, and posterior portions, bounded above by the
root of the neck, below by the diaphragm. Each
lung presents for examination an apex, a base, dia-
phragmatic, costal, mediastinal surfaces, and anterior,
posterior, and inferior borders. It is suspended within
the cavity by the root and the ligamentum pulmonale.
Front view of the heart and lungs. (Gray.)
During respiration the lung, covered by the visceral
pleura, is pressed against the walls of the thorax,
interlined by the parietal pleura, and friction is pre-
vented by a small amount of fluid, within the pleural
cavity, which continually bathes the approximating
THE ORGANS OF RESPIRATION 243
The apex (apex pulmonis) is rounded, and extends
about 1 inch to 2 inches above the anterior end of
the first rib. It is grooved by the subclavian artery
on the left side, but on the right side the impression of
the innominate vein is the most prominent groove seen.
Fissures and Lobes. The left lung is divided into
two lobes, an upper and a lower, by an oblique fissure,
which extends from the outer to the inner surface of
the lung both above and below the hilum. The right
lung is divided into three lobes, an upper, middle,
and lower, by an oblique fissure, separating the lower
and middle lobes, a horizontal fissure separating the
upper and middle lobes.
The Root of the Lung (Radix Pulmonis). This lies
a little above the centre of the mediastinal surface,
and approaches nearer to the posterior than to the
anterior border. It transmits the bronchus, the
pulmonary artery, the two pulmonary veins, usually
the bronchial arteries and veins the former supply
the bronchi and lungs with blood the pulmonary
plexus of .nerves, lymphatics, the bronchial lymph
nodes, and areolar tissue, surrounded by a reflection
of the pleura which fuses with the pericardium at
Structure of the Lungs. The color of the lungs at
birth is a pinkish white; in adult life, a dark slate
color, mottled in patches; and as age advances this
assumes a black color.
The lungs are composed of an external serous coat,
subserous areolar tissue, and parenchyma, consisting
of numbers of lobules (f to 1-i- inches in size). The
structures enclosed within the lungs consist of bronchi,
their subdivisions which end in the air cells, blood-
vessels, lymphatics and nerves, all embedded in a sup-
porting net-work of fibrous and elastic tissue. These
structures can only be seen under the microscope.
The bronchi, on passing to the periphery of the
lung, become smaller and smaller as they divide and
244 THE RESPIRATORY APPARATUS
subdivide. The walls become thinner and the car-
tilaginous rings disappear. The smallest bronchial
tubes contain muscle tissue in their walls. These
latter fibers, when stimulated by nerves from the
vagus, cause a narrowing of the caliber of the bronchial
tubes. When the bronchial tubes are so reduced
as to measure about 1 millimeter, they are termed
bronchioles. From the latter are given off small
branches which soon expand to form numbers of
lobules or alveoli. The central space of the alveoli is
called the infundibulum, and from the inner surface
of the alveolus, project small partitions which include
the air sacs or cells between them. The walls of the
alveolus are very thin and composed of fibro-elastic
tissue. The bronchi and bronchioles are lined with
ciliated epithelium and the alveoli and air cells by
flat epithelial cells, called respiratory epithelium.
The bronchi and their subdivisions are accompanied
by branches of the pulmonary artery, and pulmonary
and bronchial veins. The pulmonary arteries upon
reaching the alveoli of the lungs form a capillary net-
work which is in intimate relation with the respiratory
epithelium of the air sacs, only the thin wall of the
capillary intervening. This permits of the ready inter-
change of the carbon dioxide through the wall of the
capillary and respiratory epithelium with the intrapul-
monary air, and the oxygen from the latter is absorbed
in the same way by the red cells of the blood in the pul-
monary capillaries, and returned to the left side of the
heart. The bronchial arteries supply the walls of the
larger bronchial tubes and tissue of the lungs anasto-
mosing with the capillaries of the bronchial and pulmo-
nary veins. The bronchial veins pass back to empty
into the azygos system on the right side and on the
left they drain into the superior intercostal vein. The
pulmonary veins are supposed to contain some venous
blood derived from the bronchial venous capillaries,
besides their arterial blood.
Respiration is a process whereby the lungs receive
the oxygen from the air we breathe; it is carried to
the tissues by the hemoglobin of the red cells, where it
is given off to the tissues; carbon dioxide is taken up
by the hemoglobin from the tissues and carried by the
red cells to the lungs, where it is given off in the expired
air. Respiration, therefore, is a function indispensable
to life and plays a most important part in the main-
tenance of body metabolism, by supplying oxygen to
the tissues, and removing carbon dioxide from the
tissues in the cheinic interchange taking place between
the air, the blood, and the tissues during the act of
respiration, and circulation of the blood.
Rate of Respiration. The normal rate of respira-
ation varies at different ages as follows: At birth and
during the first year, 44 per minute; five years, 26 per
minute; fifteen to twenty years, 20 per minute; twenty
to twenty-five years, 18.7 per minute; thirty to fifty
years, 18 per minute.
Respiration is divided into: inspiration, an active
process due to muscular activity, when air enters the
lungs, due to atmospheric pressure being greater
than the contained intrapulmonary; expiration, a quiet
or passive process, due to the recoil of the elastic
tissue of the lungs, the abdominal and thoracic walls;
when the intrathoracic pressure becomes greater than
the atmospheric air pressure it allows the contained
air to escape until the intrapulmonary pressure equals
the atmospheric air pressure, then inspiration occurs
again, and the respiratory cycle is repeated.
The Volumes of Air Breathed. This is determined
by an apparatus known as Hutchinson's spirometer.
With this apparatus four volumes of air are deter-
mined. (1) The tidal volume or the amount of air
which flows into and ou^ of the lungs during an ordinary
246 THE RESPIRATORY APPARATUS
inspiration and expiration varies from 20 to 30 cubic
inches. (2) The complemental volume or the amount
of air taken into the lungs, in addition to the tidal
volume, resulting from a forcible inspiration, which
amounts to 110 cubic inches. (3) The reserve volume
or the amount of air which flows out of the lungs, in
addition to the tidal volume resulting from a forcible
expiration, which amounts to 100 cubic inches. (4)
The residual volume or amount of air remaining in the
lungs, as a permanent volume, after the most forcible
The vital capacity is the amount of air which can
be expelled from the lungs after they are filled by the
most forcible inspiration. This amounts to 230 cubic
inches (3593 c.c.). *
Changes in the Composition of Inspired and Expired
Air as a Result of Respiration.
INSPIRED AIR, 100 VOLUMES
Carbon dioxide traces
Watery vapor variable
EXPIRED AIR, 100 VOLUMES
Carbon dioxide 4.38
Water vapor saturated
Organic matter (Brubaker)
The above analyses show that the air under ordinary
conditions loses oxygen to the extent of 4.37 per cent.,
and gains in carbon dioxide to the extent of 4.38 per
cent.; it gains in nitrogen to the extent of 0.4 per cent.,
and watery vapor to the point of saturation, also
From experiments with the spirometric apparatus,
and the taking of the percentage loss of oxygen and
gain in carbon dioxide shown by the analysis of the
respired air, it is possible to figure approximately
the total amount of oxygen absorbed and carbon
dioxide given off during respiration. The minimum
daily volume of air breathed is assumed to be 10,800
liters and the maximum daily volume 12,240 liters.
Thus the minimum daily yolume of oxygen absorbed
is 510 liters, maximum 585 liters. Carbon dioxide
is exhaled amounting to 473 liters, the minimum
daily volume; 520 liters, the maximum daily volume.
Thus one can readily understand how essential it
is for human beings to obtain a fresh supply of air
to breathe in order to maintain life and carry on its
various activities. Since during every breath the
external air loses oxygen and gains carbon dioxide,
besides other waste products, the air in dwellings,
offices, etc., should be frequently renewed in order
to maintain a condition of health. If we take in at
each inspiration 30 cubic feet of air, and breathe at
the rate of 18 respirations a minute, then in twenty-
four hours 450 cubic feet (12.8 cm.) will pass in and
out of the lungs. Thus it is easy to understand how
a person laboring, or sleeping, etc., in an unventilated
room w r ould readily succumb, theoretically, by rebreath-
ing the poisoned air from his own lungs.
The Changes in the Blood during Respiration.
The blood as it is forced from the right ventricle of
the heart through the pulmonary artery to the lungs,
is dark bluish red in color. On reaching the air cells
of the lungs the blood becomes bright red in color and
is carried through the pulmonary veins to the left
auricle, then into the left ventricle of the heart, when
it passes out through the large artery (aorta) to supply
the body tissues.
The blood is changed while flowing through the
capillaries from <he venous to the arterial state. When
the dark bluish-red blood in the pulmonary arteries
reaches the capillaries of the pulmonary system where
they surround the air cells, and the thin membrane
248 THE RESPIRATORY APPARATUS
separating the capillaries from the intrapulmonary
air, the carbon dioxide is given off and the oxygen is
taken up and combines chemically with the hemo-
globin contained in the red cells, forming oxyhemo-
globin, the blood in the arterial capillaries of the
pulmonary veins immediately turns bright red as a
result of the interchange. This bright red or arterial
blood is carried to the tissues by the arteries and
CAP.LLARY BLOOD VESSEL (j)0Q(o) Q QQ><3) 000 <S0
Diagram of the essentials of a respiratory apparatus. (F. H. G.)
This power possessed by the blood of absorbing
and giving up oxygen and carbon dioxide through the
capillary walls from and to the air and tissues respec-
tively is based on the well-known fact that liquids
will absorb or dissolve at any constant pressure
unequal volumes of different gases in accordance with
their solubilities, and with variations in temperature
The Relation of the Nerve System to Respiration.
The rhythmic movements of respiration are controlled
by nerve impulses which arise in groups of nerve cells
in the central nerve system, and are transmitted to
the inspiratory and expiratory centres in the medulla
oblongata, which are stimulated into activity.
The inspiratory and expiratory centres are included
under the term respiratory centre.
The vagus nerve is the important nerve which
transmits nerve impulses from the inspiratory centre
in the medulla to the lungs. It contains excitor and
inhibitor fibers; the former, when stimulated, increase
the rate of inspiration and the latter decrease it.
Respiration is believed to be due to a stimulus
resulting from the alternate distention and collapse
of the walls " of the pulmonary alveoli a mechanic
The inspiratory centre can be influenced directly
by nerve impulses being transmitted from the brain
in response to voluntary acts, or emotional states,
sighing, etc., also indirectly by nerve impulses reflected
to the centre from the surfaces of the skin and mucous
membranes through afferent nerves; as cold applied
to the skin, irritating gases to the nasal and bronchial
mucous membranes, and collapse or distention of the
1. Name the organs of respiration.
2. What effect has the nasal mucous membranes upon the air
3. What is dyspnea?
4. What is the organ of the voice?
5. Give the relations of the larynx.
6. How many cartilages form the larynx? Name them.
7. Which cartilage forms the Adam's apple?
8. What is the rima glottidis?
9. Describe the true and false vocal cords.
10. Which muscles open the glottis? Close it?
11. Which muscles regulate the tension of the vocal cords? Relax
12. What do you understand by the term phonation?
13. How is articulate speech produced?
14. Name the number of rings in the trachea.
15. What variety of epithelium lines the trachea and what is its
16. Are there glands in the trachea, and to what variety do they
17. Where do the bronchi enter the lungs?
18. Are the pleurae closed sacs?
19. What do you understand by the terms visceral and parietal
20. Where is the pleural cavity located? Does it contain fluid?
21. What membranes cover the lung?
22. Name the parts of each lung.
23. What structures form the root of the lung?*
24. How many lobes has the right lung? The left?
25. Give the microscopic structure of the lung.
250 THE RESPIRATORY APPARATUS
26. What is a bronchiole? Lobule?
27. Where is the infundibulum in the lobules of the lungs? The
28. Name the variety of epithelium lining the bronchi, bronchioles,
alveoli, and air sacs.
29. What relation do the capillaries of the pulmonary artery and
vein bear to the air sacs of the lobules?
30. What relation do the respiratory epithelium and capillaries
bear to respiration?
31 Describe respiration.
32. Give the normal rate of respiration per minute at birth. Five
years. Fifteen to twenty years. Twenty to twenty-five years.
Thirty to fifty years.
33. Name the divisions of respiration.
34. What do you understand by the terms tidal volume? comple-
mental volume? reserve volume? residual volume? in relation to
35. What is the average vital capacity of the lungs? What is
meant by it?
36. Give the minimum and maximum daily volume of air breathed .
37. What gaseous interchange takes place during each respiration