"

*

0J"

PRESENTED TO

The UNIVERSITY of MLrailil

EDMONI) J, GOOLD.

G "FG8UTM.Ce.Tt BROACW*Y

WONDERS

OF THE

HUMAN BODY.

PROM THE FRENCH OF

A. LE PILEUR,-

DOCTOR OF MEDICINE.

ILLUSTRATED BY
FORTY-FIVE ENGRAVINGS BY LEVEILLE,

NEW YORK:

CHARLES SCRIBNER AND CO.
187 i.

3 BIOLOGY

V

Illustrated library of Wonders.

PUBLISHED BY

654 BROADWAY, NEW YORK.
Each one volume 12mo, Price per volume, $1.50.

Titles of Books. No. of Illustrations

THUNDER AND LIGHTNING, ....... 39

WONDERS OF OPTICS, . TO

WONDERS OP HEAT, ...... .90

INTELLIGENCE OP ANIMALS, ...

GKEAT HUNTS, . . . .22

EGYPT 3,300 YEARS AGO, ..... 40

WONDERS OP POMPEII, . . .22

THE SUN, BY A. GUILLEMIN, . ... 53

SUBLIME IN NATURE, ..... .50

WONDERS OP GLASS- MAKING, . ... 63

WONDERS OP ITALIAN ART, . » . . . . . .28

WONDERS OP THE HUMAN BODY, . 45

WONDERS OP ARCHITECTURE, . . .50

LIGHTHOUSES AND LIGHTSHIPS, ...... 60

BOTTOM OP THE OCEAN, ...... 6S

WONDERS OP BODILY STRENGTH AND SKILL, . . TO

WONDERFUL BALLOON ASCENTS, ... .30

ACOUSTICS, ......... 114

WONDERS OP THE HEAVENS, ....... 48

THE MOON, BY A. GUILLEMIN. . ... 60

WONDERS OP SCULPTURE . . .... 61

WONDERS OP ENGRAVING, ..... ->'2

WONDERS OP VEGETATION, .... 45

WONDERS OP THE INVISIBLE WORLD, ..... 97

CELEBRATED ESCAPES, ...... 26

WATER. ....... ,77

HYDRAULICS .... ... 40

ELECTRICITY, ....... 71

SUBTERRANEAN WORLD, .... 27

* In Press fur early Publication.

ITie above work* sent to any address, postpaid, upon, receipt of the price by the
publishers.

PUBLISHERS' PREFACE.

THERE is an increasing tendency in the present day to make
common property of special knowledge. Even such infor-
mation as formerly belonged to certain professions alone is,
at least in its rudiments, becoming more generally diffused;
and on the part even of those professions the tendency is
recognized as within reasonable bounds deserving of encour-
agement.

To take "the human body" as an illustration, medical
men find that the useful feature of their art is facilitated by
the dissemination of information regarding its structure and
functions. On the other hand, the public daily see more and
more clearly that " prevention is better than cure," and that
to prevent derangements of the wonderful machine, with the
guidance of which each individual is intrusted, more ac-
quaintance with its mechanism and laws of normal action
is indispensable. Apart from its utility, a knowledge of

\ anatomy and physiology is gradually becoming a necessary

: part of a liberal education.

To meet these requirements the Publishers now present
this translation from the French of a book which, in the
original, has attained to great popularity. While sufficiently

VI PREFACE.

minute in anatomical and physiological details to satisfy
those who desire to go deeper into such studies than
many may deem necessary, this work is nevertheless written
so that it may form part of the domestic library. Mothers
and daughters may read it without being repelled or
shocked; and the young will find their interest sustained
by incidental digressions to more attractive matters. Such
are the pages referring to phrenology and to music, which
accompany the anatomical description of the skull and of
the organs of voice; and the chapter on artistic expression
which closes the book.

Attention may also be directed to the numerous accurate
and also simple engravings, which have been introduced in
the hope of elucidating the verbal descriptions in the text.

CONTENTS.

CHAPTER I.

PAGE

Introduction. — Opinions of the ancients concerning the human
body. — Summary of general anatomy. — Substance of the body or
organized matter. — Anatomical elements. — Nutrition.— Fluids.
— Tissues, I

CHAPTER II.

Form of the body.— Its beauty. — The master-pieces which it has
inspired. — Description of the skin — its functions, 13

CHAPTER III.

Structure of the body. — Bones, cartilages, joints. — Muscles, ten-
dons, aponeuroses, 25

CHAPTER IV.

Spinal column. -^Thorax. — Upper limb; shoulder, arm, fore-arm,
hand. — Lower limb; hip, thigh, leg, foot, 41

CHAPTER V.

Motion. — Effort.— Locomotion; standing, walking, running, jump-
ing, swimming, 57

CHAPTER VI.

The head. — The skull, bones of the skull, sutures, arch of thc
skull, base of the skull. — Measurement of the skull; facial angle,
angle of Daubenton; comparison of the superficies of the skull
and of the face. — System of Gall. — The face, bones of the face,
upper jaw, lower jaw, 67

CHAPTER VII.

Digestion. — Waste of the organism repaired by alimentation. —
Hunger. — Thirst. — Organs of digestion; abdominal cavity, peri-
toneum. — Digestive apparatus. — Mouth, lips, cheeks, teeth,
palate, soft palate, tongue. — Pharynx. — (Esophagus. — Stomach.
— Intestinal canal; small intestine, large intestine, intestinal con-

Vlll CONTENTS.

PAGE

volutions, mesentery, omen turn. — Mucous membrane. — Liver. —
Pancreas. — Spleen. — Kidneys. — Mechanism of digestion. — Di-
gestion of the stomach, gastric juice, peristaltic movement, chyme.
— Intestinal digestion, bile, pancreatic juice, chyle. — Absorption;
endosmosis, exosmosis, functions of the veins and lymphatic
vessels in absorption, rapidity of absorption, 73

CHAPTER VIII.

Respiration. — Thoracic cavity; pleura. — Organs of respiration:
lungs, trachea, bronchia. — Respiration; influence of respiration
on the blood, Lavoisier's theory, theory of catalytic phenomena;
mechanism of respiration, respiratory sounds, frequency of re-
spiration; capacity of the lungs; modification of the air in the
lungs. — Influence of atmospheric pressure. 6n respiration; moun-
tain-sickness, 89

CHAPTER IX.

Circulation. — Organs of the circulation; heart, pericardium; arteries,
capillaries, principal arteries; veins, principal veins; portal sys-
tem; lymphatic vessels and ganglia. — Mechanism of the circula-
tion; discovery of the circulation, action and sounds of the heart,
arterial circulation, pulse, capillary circulation; venous circula-
tion, valves of the veins; discharge of chyle and lymph into the
veins. Sanguification; circulation in the pulmonary artery,
capillaries, and pulmonary veins. — Influences which accelerate or
retard the beating of the heart, IO2

CHAPTER X.

Nervous system. — Cerebro-spinal nervous centre. — Cerebrum. —
Cerebellum. -^-Isthmus of the encephalon. — Medulla oblongata. — -
Spinal cord. — Membranes; dura mater, arachnoid, pia mater. —
Nerves; cranial nerves, spinal nerves, great sympathetic. — Func-
tions of the nervous system; functions of the spinal nerves of
motion and of sensation; function of the cranial nerves; functions
of the spinal marrow. — Functions of the encephalon; medulla
oblongata, pons Varolii, peduncles of the cerebrum and cere-
bellum, corpora quadrigemina, pineal gland, optic thalami,
cerebrum and cerebellum. — Functions of the great sympathetic.
— Reflex power. — Nerve force.— Memory, 119

CHAPTER XI.

Sense of sight. — Organ of vision.— Globe of the eye; sclerotic;
cornea; choroid ; ciliary ring; ciliary body ; ciliary process; iris;

Eupil ; uvea; pigment; retina; vitreous body; hyaloid mem-
rane ; crystalline ; anterior and posterior chambers ; aqueous
humour. — Muscles of the eye. — Conjunctiva. — Eyelids, eyelashes.

CONTENTS. , IX

PAGE

— Lachrymal apparatus. — Vision; functions of the retina, .re-
versed images ; functions of the iris ; optic centre, visual angle,
visual impressions, single or mixed, adaptation of the eye to dis-
tances, myopia, presbyopia ; achromatism ; single and double
vision with two eyes, stereoscope; alternation in the action of
the eyes ; persistence of impressions on the retina ; accidental
images ; irradiation ; accidental aureola ; Daltonism ; apparent
motion of objects! — Optic nerve. — Movements of the eye. — Ex-
tent of vision, 152

CHAPTER XII.

Sense of hearing. — Organ of hearing. — External ear; pavilion of
the ear, auditory canal. — Middle ear; tympanum, drum, or
membrana tympani, fenestra ovalis, fenestra rotunda, Eustachian
tube, the small bones of the ear, muscles and movements of the
small bones. — Internal ear; labyrinth, vestibule, semicircular
canals, cochlea, membranous labyrinth. — Auditory nerve. —
Noises and sounds; duration, pitch, intensity and quality of
sound ; passage of sound through air, water, solid bodies ;
gravity, sharpness of sound. — Mechanism of hearing; functions
of different parts of the ear; movement of sounds in the ear;
propagation of sounds to the auditory apparatus by the vibrations
of the bones of the skull. — Opinions of physiologists on the
functions of different portions of the labyrinth ; theory of Helm-
holtz. — Fineness and delicacy of hearing. — Correctness of the
ear. — Estimation of the intensity, the distance, and the direction
of sounds; ventriloquism. — Duration of auditory impressions. —
Sensations having an internal origin. — Parallel between the eye
and ear, 182

CHAPTER XIII.

Sense of smell. Olfactory organs. — Nose; nasal fossae, turbinated
bones, pituitary membrane. — Olfactory nerve. Odoriferous
principles ; their development, their action on the nervous sys-
tem.— Smell, — its seat ; duration of olfactory impressions. — Uses,
and acuteness of smell, 203

CHAPTER XIV.

Sense of taste. — Organ of taste. — Special nerves of the organ. —
Flavours. — Taste, 210

CHAPTER XV.

Sense of touch. — Difference between touch and feeling. — Tactile
sensibility and general sensibility. — Organ of touch. Sensation
of contact ; difference in the sensibility of different regions of the
body; simple contact, shock, vibration. — Sensation of pressure;

X CONTENTS.

PAGE

relative aptitude of different regions in appreciating it; \ariable
sensation according to the form of the body and the extent of
its surface. — Sensation of temperature, variable according to the
temperature of the skin, the density of bodies, and the surface in
contact ; identical sensation from contact with a body very hot
and very cold ; relative sensibility of different regions to tem-
perature.— The touch; its delicacy. — The touch compared with
the other senses ; illusions of touch ; persistence of tactile impres-
sions, sensations from internal or subjective causes ; causes which
modify feeling, .217

CHAPTER XVI.

Voice and speech. — Organ of voice; larynx, cavity of the larynx,
glottis, vocal cords ; the larynx at different ages and in different
sexes. — Physiology of the larynx ; mechanism of the voice ;
opinions as to the formation of the voice. — Galen, Fabricius
Acquapendente, Dodart, Ferrein, Biot, Miiller, Savart, Masson,
and Longet. — Theories founded on laryngoscopic observations. —
Formation of sounds in whistling. — Voice; speaking voice,
mechanism of articulate sounds, vowels, consonants, timbre of the
vowels; the tongue as an organ of pronunciation. — Singing;
chest voice, falsetto voice, mixed voice ; different theories on the
formation of the falsetto : Miiller, M. Segond, M. Longet, M.
Fournie, M. Bataille, M. Mandl. — Timbres of the voice : high
pitch, grave pitch. — Compass of voices: bass, baritone, tenor,
contralto, mezzo-soprano, soprano. — Ventriloquy, 228

CHAPTER XVII.

Physiognomy ; study of it in works of art. — Movements of expres-
sion, their seat. — Colouring of the skin ; paleness, redness. — Ex-
pression of the muscles; effort, muscles of the face. — Physiognomy
of the senses. — Expression of the eyes, vision, easy or difficult,
blindness. — Expression in the act of hearing, easy or difficult,
hearing of an orator, musical hearing. — Expressions of smell and
taste. — Expressions relating to the touch 247

LIST OF ILLUSTRATIONS.

FIG. rAG3

1. Blood seen under the microscope, 4

2. Bony tissue as seen with the naked eye, 8

3. Osseous and cartilaginous tissues as seen through the micro-

scope, 8

4. Laminated fibres in the first stage of development, .... 9

5. Stripped muscular tissue as seen under the microscope, . . 10

6. Nervous tissue seen under the microscope, 1 1

7. A nerve and its ramifications seen by the naked eye, ... 12

8. Apollo Belvedere, 15

9. The Venus of Milo, 17

10. The Skin, 21

11. Skeleton, 27

12. Elbow-joint, 33

1 3. Biceps muscle of the arm, 35

14. Lower portion of the leg, 37

15. The hand, palmar aspect, 46

1 6. The hand, dorsal aspect, 46

17. Knee-joint, 52

1 8. Skeleton of the foot, 54

19. The foot, 55

20. The leg in standing, 61

21. Section of the trunk and its cavities in the median line, . 74

22. Section in the median line through the inferior portion of the

nasal fossne, the mouth, pharynx, larynx, oesophagus, and

trachea, /6

23.. Transverse section of the thoracic and abdominal cavities, . Si

24. Lungs and heart, 91

Xll LIST OF ILLUSTRATIONS.

FIG. PAGE

25. Section showing the ramifications of the bronchi in the lungs, 93

26. Heart and principal arterial and venous trunks, 103

27. Transverse section of the heart, 105

28. Imaginary diagram of the course of the blood in the circula-

tion, 116

29. Cerebro-spinal nervous centre, 120

30. Nervous system, 121

31. Upper surface of the brain, 123

32. Lower surface of the brain, • . 124

33. Section of the encephalon in the median line, 126

34. Vertical section of the eye on the median line, 153

35. Rods of Jacob under the microscope, 156

36. Diagram illustrating "blind point " in retina, 161

37. Course of the luminous rays in the eye, 162

38. Diagram illustrating the visual angle, 164

39. Accommodation of the eye to different distances, . . . . 167

40. Diagram illustrating single vision with two eyes, . . . . 1 70

41. Irradiation, 176

42. Section showing the different parts of the ear, 183

43. Experiment on the sensations of touch, 226

44. Section of larynx in the median line, 229

45. The glottis and vocal cords, 242

THE

HUMAN BODY.

CHAPTER I.

INTRODUCTION.

Opinions of the ancients concerning the human body. — Summary of general
anatomy. — Substance of the body or organized ?natler. — Anatomical
elements. — Nutrition. — Fluids. — Tissues.

IT has been said with truth, that the human mind, which
can survey the heavens and calculate the motion and density
of the stars, finds itself confounded when, returning from
these distant journeyings, it enters its own proper dwelling-
place. Man's own organization is still among those mysteries
of nature which he is least able to penetrate, in spite of his
incessant efforts to lift the veil which hides it. In all ages
he has sought to know himself; in all times he has studied
the relations between his own existence and that of the
world; and those universal influences which, though evident
to him, are nearly all inexplicable in their action upon living
beings.

Carried by their imagination into this way of comparing
the human body with the rest of creation, Aristotle and some
other philosophers saw in man an epitome of the wonders
of the universe. He was for them the microcosm, the dimi-
nutive and summary of the entire world.

Paracelsus and the astrological doctors developed from
their stand-point the ideas of the Greek philosophers, and
pushed to its extreme limits the doctrine of sidereal influence

2 THE HUMAN BODY.

upon man. According to them, the body had, like the earth,
an axis and two poles ; the head, the seat of the soul, corres-
ponded to the heavens where divinity resided, &c.

Since that time, and especially in our own day, the ima-
gination has given way to a rigorous method of study and
to positive ideas. But whether we venturously follow Aris-
totle and Paracelsus, or whether we prefer the exact results
of science to their poetic theories, we shall always see in
the human body the highest and most perfect creation of
nature among living beings, and we shall admire the efforts
and the discoveries which the study of its organization has
enabled the mind to make from the time of the masters of
antiquity down to our own day.

In the human body, as in animals and in the vegetable
kingdom, the organized matter is composed of what are
termed proximate (or immediate) principles and anatomical
elements. Of these proximate principles some are of mineral
origin, as oxygen, water, the carbonates, the chlorides, the
phosphates, &c. They penetrate the organism, and there
furnish the materials, by the aid of which other principles of
a different order are formed. These last essentially consti-
tute the body, hence the name organic substances is specially
applied to them. There is nothing in the mineral kingdom
analogous to these organic substances, though they borrow
their original elements from it. They are solid or semi-solid
(globuline, musculine), liquid or semi-liquid (fibrine, albu-
men, caseine), colouring or coloured (hematosine, biliver-
dine). They decompose where they are formed, and give
birth to another class of proximate principles. These last
are of very different natures, and possess different attributes;
they are acids, salts, alkaloids, fatty bodies; they are urea,
creatine, stearine, cholesterine, and the sugar of the milk
and of the liver, lactic acid, uric acid, &c.

This double and continuous movement of combination
and resolution of proximate principles results in the forma-
tion of the anatomical elements. This is the term applied to
very minute bodies, free or attached, which present special
geometrical, physical, and chemical characters, as well as a
structure which has no analogy to that of minerals. — They

NUTRITION — HUMOURS. j

are the smallest organic subdivisions of which the tissues
and fluids are capable by anatomical analysis. Their reunion
and combination form the solids and liquids of the organism.
By assimilation they borrow their substance from the
molecules of the proximate principles, while at the same
time and in equal proportions they abandon other molecules
of these same principles by a process of separation.

This assemblage of phenomena is termed nutrition. In
this manner water, carbon, lime, phosphorus, iron, and the
other principles, co-operate in forming globuline, fibrine,
musculine, and the other organic substances, which by their
combination constitute the anatomical elements of the blood,
the muscles, the bones, the nerves, the body in a word; this
is assimilation.

At the same time other molecules of the same principles,
in equal proportions, abandon by a separatory process the
substance of the organism, and unite to form the milk,
saliva, tears, bile, and the other secretions, which are to be
completely excreted as improper for nutrition, or partially
thrown oft and partially returned to the system.

As to the anatomical elements, some of them have a form
which may be described, as globule, fibre, tube, and cell;
others are amorphous, and serve to fill the spaces between
those first-named.

We see therefore that the immediate or proximate prin-
ciples and the anatomical elements constitute all organized
matter whether solid or fluid.

The fluid portions of the human body greatly exceed the
solid ; they are computed at nine-tenths of the whole weight.
Water enters largely into the composition of these fluids,
a portion of which only is contained in the vessels or
reservoirs specially set apart for each of them, while the
remainder penetrates the solid parts and forms part of their
substance.

The term humours — fluids— is applied to the liquid or
semi-liquid portions of the organism formed by the mingling
and dissolution of immediate principles, and they ordinarily
hold the anatomical elements in suspension. The solid
portions are called tissues.

4 THE HUMAN BODY.

These fluids are classed, according to the part they play in
the human economy, into constituent fluids, secreted fluids
or secretions, excretions, and intermediate products, which
partake of the nature of the other three. The constituent
fluids are three in number — the blood, chyle, and lymph.
The blood is the nutritive fluid of the body; it contains all
the immediate principles that are found in its organism. In-
cessantly renewed by digestion and respiration, it supplies
to each organ assimilable matter, and to the special labora-
tories the materials for the secretions, and carries off the
results of disassimilation which are to be thrown out of the
organism. It is therefore at once a reparative and a purify-
ing fluid. The term " fluid flesh," which has been applied

Fig. i.— Blood seen under the microscope.

to it, is incomplete, for it contains not only the muscular
tissue, but the essential elements of all the other tissues are
found in its mass.

The blood is heavier than water, its specific gravity being
1052 to 1057, while that of water is 1000. In the blood-
vessels the blood is composed of — ist. anatomical elements,
red and white corpuscles. 2d. Of a fluid, of which 779 parts
in weight in 1000 are water in men, and in women 791
parts in 1000. This fluid is the plasma, the plastic substance,
the nourishing juice in which are found all the immediate

BLOOD, g

principles of the blood. Among these, principles are lime,
ammonia, soda, potash, phosphorus, magnesia, iron and other
metals in the form of salts; chlorides, sulphates, carbonates,
phosphates, &c.; and mingled with these are the principles
of the secretions and organic substances, of which the most
important, from their quantity, are — fibrine, 2-5 parts in 1000,
and albumen 69 to 70 in 1000.

The blood owes its colour to the red corpuscles, which are
themselves coloured by a substance which De Blainville has
named hematosine, and which contains 7 parts in i oo of iron.
These corpuscles are round flattened disks of *oo6 to '007
of a millimetre in diameter, and a thickness of '002 milli-
metre. Under the microscope they appear grouped together
without order, or piled one upon another like pieces of
money, and are of a red colour in reflected light. The white
corpuscles are smooth, spherical, of a yellowish-white colour
in a reflected light, and from '008 to "014 of a millimetre in
diameter.

The colour of the blood is a beautiful crimson red in the
arteries, but of a darker colour in the veins. We shall have
occasion to examine it from this point of view in treating of
the circulation.

When blood which has been drawn is allowed to stand in
the vessel, it separates into two distinct parts : the one, semi-
solid, is called the crassamentum— the clot; the other fluid,
is called serum. The clot is the coagulated fibrine which
carries with it the red globules which were held in suspension
in the blood. When the coagulation is delayed, these glob-
ules, being heavier than the other portions of the blood, fall
toward the lower part of the vessel; and the fibrine, freed
from them, coagulates and retains its own proper colour, and
the clot is composed of two layers — the superficial layer is
of a grayish or white colour and semi-transparent, and is
termed the "buffy coat." It is formed of pure fibrine mingled
with the white globules; the other is composed of fibrine and
of the red globules which give it its colour. The serum
is a transparent, greenish-yellow fluid, sometimes a little
whitened by minute fatty specks; from which circumstance,
and from some other points of analogy between them, it has

6 THE HUMAN BODY.

been called the whey. It is a little less dense than the clot,
and contains among other principles a great deal of albumen.
The serum is the plasma without the fibrine.

The chyle is a white opaque fluid closely resembling milk,
which is separated from the food during the process of diges-
tion, and is drawn by the chyliferous vessels from the surface
of the smaller intestine, and serves to form the blood. As
it advances toward the point where it mingles with the blood,
it resembles this fluid more and more in its composition; it
takes a roseate tint, and, if left to itself, it separates into
fibrinous clot and albuminous serum.

The lymph is a clear, transparent fluid, slightly tinted with
green or yellow. Drawn from the organs by the lymph-
atic vessels, and especially from the skin and the surface
of the mucous and serous membranes, the lymph is poured
into the mass of blood by two principal canals. Like
the chyle it contains white globules and minute specks of
fat. When extracted from the lymphatic vessels, it also
separates into fibrinous clot and serum, containing a little
albumen.

We see therefore that chyle and lymph are imperfect blood.
The chyle leaves the digestive apparatus in a crude state, and
goes to the blood-making laboratories for its perfection. The
lymph comes from the extreme limits of the organs to these
same laboratories, and, uniting with the chyle, is poured into
the blood — the constituent fluid par excellence.

The secreted fluids or secretions are produced by special
apparatus from the materials furnished by the constituent
fluids. They differ from these last in being only a medium
for the elements which they hold in suspension, these elements
not being essential to them, as the globules are to the blood,
for example. They all contain one or several organic fluid
substances, to the nature of which the secreted fluid owes its
essential properties. These humours are very numerous, and
play a very distinct part in the human economy. They are
normal or morbid, as they owe their origin to the regular
function of the organs or are modified by the action of disease.
We shall mention only milk, which resembles the blood by
composed largely of serum, and which cannot be

CHYME — TISSUES. 7

replaced by any substance for the alimentation in the first
stages of infancy; — the aqueous and vitreous humours of the
eye, the synovia which bathes and lubricates articulated sur-
faces, the tears, and the saliva, which we shall see later takes a
part in digestion, and in which Mons. Longet has shown the
existence of minute and therefore harmless proportions of
sulpha-cyanide of potassium, one of the most virulent poisons.
In popular language the term humour is applied exclusively
to the purulent fluids, morbid products which differ in some
particulars according to the conditions under and the organs
in which they are formed. It is unfortunate that they
should monopolize a term which belongs to all the organic
fluids.

We shall merely point out the intermediate products, among
which figures the chyme, a semi fluid substance formed in the
stomach during digestion, and the excretions which the system
rejects, after having separated from them nearly all assimil-
able principles.

The tissues are the solid parts of the body, formed of
anatomical elements either bound together or simply in
juxtaposition. The tissues are classed according to the
elements peculiar to them, according to their texture, that
is to say the mode in which these elements are arranged;
and according to their essential properties, which are either
physico-chemical, such as consistence, extensibility, retrac-
tility, elasticity, and hygrometricity, or organic, like the
properties of absorption, of secretion, of development, of
regeneration, of contractility, and of innervation. These
properties are variable according to the tissues, which are
more or less tenacious, more or less extensible, and so forth.
Or they are peculiar to certain tissues, and independent, for
a tissue may be retractile and not extensible or elastic, and
vice versa. Constituent tissues are those which, composed
of the fundamental elements, fibre, cell, and tube, form the
essential organism. Produced tissues are those which eman-
ate from the first, and may be detached from them without
destroying them, and are only accessory or complementary
parts. These products are normal or morbid, according to
their nature and substance.

THE HUMAN BODY.

Air.ong the numerous tissues which exist in the economy
we cite the following: —

Fig. 2. — Bony tissue as seen with the naked eye.

Fig- 3- — Osseous and cartilaginous tissues as seen through the microscope.

A, Cells of cartilaginous tissue.

B, Section of a canal of Havers, showing the disposition of the s tarty

cells in the substance of a bone.

C, Starry cells magnified.

Osseous or bony tissue, which is composed principally of
an anatomical element called osteoplasm. It is compact in

CELLULAR, ADIPOSE, MUSCULAR TISSUE.

some parts of the bones, and spongy in others. This tissue
is traversed by infinitely ramified conduits, called the canals
of Havers, which contain the blood-vessels and the medullary
substance or marrow.

Cartilaginous and fibre-cartilaginous tissue.

Cellular or connective tissue, more exactly named laminated
tissue, formed of laminated fibres, long, flattened, undulated
filaments in bundles, and of fibres appertaining to elastic
tissue. In nearly every part of the body this substance fills
the spaces between the tissues or between the bundles of the
fibres of which they are made up : on the surface of the body
and of its cavities, and around the organs, it is disposed in
enveloping membranes.

Adipose tissue is formed of cells
or vesicles containing fat. It is
never found except in the cellular
tissue and at the points where this
last is least dense.

These two tissues united are com-
monly designated by the term fat,
or fatty layer, but they are distinct
notwithstanding, and neither wasting
nor increase of fat causes any change
in the mass of the cellular tissue, but
only in the quantity of fat contained ,-,.

•; "_ J _. . Fig. 4. — Laminated fibres in the

111 the Cells Of the adipose tiSSUe. first stage of development.

Epithelial tissue has for its ana-
tomical elements, cells or free nuclei, which form by juxta-
position either a very thin single layer, or several superposed
layers. It is of this tissue that the epidermis and the
epithelium, a kind of internal epidermis, are essentially com-
posed.

Muscular tissue. This constitutes the muscles, or. the
flesh, properly speaking. It is composed of elements called
muscular fibres, which are of two sorts, the smooth, formed
of fibre-cells, and the striped, formed of bundles of fibrils.
The fibrils are the fundamental element of the muscular
tissue; their primitive microscopic bundles unite in secon-
dary bundles visible to the naked eye, and are known in

10

THE HUMAN BODY.

descriptive anatomy under the name of fibres of the muscles.
The fibrils are contractile but not elastic, and their primitive
bundles have a homogeneous envelope of elastic but not
contractile tissue called sarcolemma.

Fibrous tissue has the same ele-
ments as the cellular tissue, united
in compact bundles visible to the
naked eye, strongly adherent among
themselves, and interlaced in every
direction. Fibrous tissue is found
especially in the articulating and inter-
osseous ligaments and in certain en-
veloping membranes, as the sclerotic,
for example, which forms the white
of the eye.

Tendinous and aponeurotic tissue
is made up of a variety of very thin
laminated fibres, with puckered edges,
undulated and adhering directly at
one extremity to the sarcolemma of
the striped muscular fascicles, and to
the osseous substance at the other.
These fibres unite in little flattened
polyhedral bundles, from 'ooi to "002
of a millimetre in breadth, from which
the tendons and aponeuroses, which
are of a tendinous nature, are formed.
Tendinous tissue is in extensible
lengthwise, and inelastic.

Nervous tissue is essentially formed
of tubes, which are large and small.
They have homogeneous, thin, trans-
parent walls, and contain a viscous,
fatty fluid, which is the medullary substance or the whitr
substance of Schwann, in which there is a sort of stem — the
axis-cylinder. In the spinal marrow and in the brain the
walls of the tube are wanting, and only the medullary sub-
stance and the axis-cylinder remain. As we approach the
outside of the body we find, on the contrary, that the tubes

Fig. 5. — Striped muscular tis-
sue as seen under the
microscope.

A, Fibril deprived of the sar-
colemma, to show the disks
of which it is composed.

A', One of these disks.

B, Several fibres less magni-
fied.

NERVE-TISSUE.

II

become more homogeneous in structure, until at their ex-
tremity they are reduced to a filament in which the walls, the

Fig. 6.— Nervous tissue seen under the microscope.

a. b, SpJierical nerve-cells.

c, Bi-polar cell.
/>, Multi-polar cells.

h, Cells of the ganglia and nen>e-jib*'es.

i, Nerve-tube and axis-cylinder.

k, Termination of a nerve-fibre in an organ.

cylindrical axis, and medullary substance are not distinguish-
able At certain points of the nervous system the tubes
differ anatomically, according as they belong to the nerves
of sensation or the nerves of motion.

Other elements also are found in the nervous tissue — (he
ganglionic cells or corpuscles* and the fibres of Remak.

The ganglionic corpuscles •, so called because they are found
in the substance of the ganglia, receive the sensitive tubes
as they come from the brain or spinal marrow. These tubes
unite with the walls of the corpuscle at one of the points
or poles of its periphery, and emerge from it at the opposite
pole.

12

THE HUMAN BODY.

The ganglionic corpuscles are divided into bi-polar or
multi-polar, according as they receive one or several tubes.

Fig. 7.- A nerve and its ramifications seen by the naked eye.

The fibres of Remak appear to be one of the constituent
elements of the filaments of the nerves of motion.

CHAPTER IT.

Form of the body — its beauty. — The master-pieces which it has inspired. —
Description of the skin — its functions.

Nature, in modelling animals, has marvellously adapted
their forms to the functions and to the mode of life to which
.she has destined them; but no creature has received in the
same degree as man, that mingling of strength and of elegance
in contour, of grandeur and delicacy in the lines, and in no
other has she taken such care to distinguish the two sexes in
bestowing upon them her most precious gifts. It is of the
human race alone that BufTon could say: "Man has strength
and majesty; beauty and the graces are the dowry of the
other sex."

The fabulist, using the poet's privilege, makes the lion say —

''Lions might hold the upper hand,
If they but had the art to paint."

Doubtless in comparing himself with certain animals, man
cannot ignore his inferiority in muscular strength and in the
arms which nature has given him; but what matters it? He
feels his superiority to these beings, though they are stronger
and better armed than he. He knows how to avoid their
attacks and to triumph over their brute force. He constrains
them to his service, and disposes of their lives and of their
bodies, by obeying not a blind instinct but the voice of reason.
If he believes himself first among the dwellers on his planet,
it is not his vanity which persuades, but his intelligence that
proves it to him, and gives him the right to treat all other
creatures as their master.

We admire the majestic bearing of a tree, the elegance of

14 THE HUMAN BODY.

a flower, the plumage and flight of a bird, the stately tread
of some huge mammal, but nothing impresses us so much
as the human form. It is not from sympathy with beings
of our own species that we find them more beautiful; the
judgment that we pronounce upon their beauty is not due
to the inclination of one sex to the other; this sympathy and
this inclination are common to most of the superior animals,
but man alone appreciates the difference between individuals
as between species; it belongs to him only to class them
according to their merits, and to distinguish perfection from
deformity ; he alone possesses the sentiment of the beautiful,
that faculty which permits him to admire the Creator in his
works, and givqs him the right to place himself in the first
rank of animated beings.

The plastic arts receive their most elevated inspirations
from the human form, and it is to the efforts of painters
and sculptors to reproduce it in its perfection that we owe
the treasures of our museums. It is often said of these
master-pieces that they are the ideal of beauty, but we are not
to understand from that something superior to nature itself.
The artist may appreciate the relative beauty of the models
which offer themselves to his eyes, but in ceasing to follow
nature and in endeavouring to become her superior, he could
only bring forth an imaginary product, a monstrosity. Ana-
tomy, should be his first study; if he forgets its precepts he
becomes incorrect, like the musician who offends against the
laws of harmony. The ideal is not therefore a forin more
perfect, it is the perfection of the natural form itself which the
arlist strives to attain, either by drawing inspiration from a
single model, or by uniting in a single figure all the details which
he has borrowed from different individuals. Far from seeking
to surpass nature he feels that his hand is powerless to render
completely the impression which his practised eye receives.

Within certain limits he may nevertheless exaggerate or
weaken some detail of form, and that too without ceasing to
imitate nature, who shows him in this manner how he may
embody the character and the physiognomy. The painter
and the sculptor therefore may rightly allow themselves a
certain latitude in lines and proportions; it is a poetical

Fig. 8.-— Apollo BjlvcAere,

Fig. 9. — The Venus of Milo.

THE HUMAN FORM SKIN. 19

license, analogous to that which allows a musician to obtain
grand effects by momentary discords. To us then it seems
that in questions of this nature the critic should proceed with
a great deal of reserve. The right of the anatomist to point
out an irregularity cannot be contested, and the artist should
be warned that to genius alone can such be permitted ; but
even if we admit that all the criticisms addressed to painting
or to sculpture in the name of the natural sciences are well
founded, who could, in the presence of a master-piece,
obstinately dwell upon a fault of detail?

As regards the inspiration drawn from the human form, the
beauty of Raphael's Madonnas and the admirable paintings,
of the Venetians impress us perhaps still more than statuary.
Under the pencil of the great masters it is man himself that
we see. What is more beautiful than the "Vierge a la
Chaise," or than that "Violante" painted by Giorgione, of
which Venice formerly possessed the glowing figure?

In sculpture the form alone is seen, painting adds the
illusion of colour and the transparency of tone; the figures
of the statuary have exactness in movement and flexibility
of form, the painter vitalizes his creations, gives light and life
to the eye, and makes the blood circulate through the skin,
which he seems to steal from the living model.

The skin is a membraneous tissue, resistant and flexible,
varying in density and thickness according to locality, which
covers the whole body and completes the form by softening
the contours. It adheres to, and is intimately united with,
the subcutaneous cellular tissue by fibrous prolongations.
At some points it receives aponeurotic insertions, as in the
palm of the hand and the sole of the foot; at others, as on
the neck, for instance, the muscular fibres are attached to
the skin, and mingle with the fibres of its deeper layer.
There are folds in the skin, sometimes temporary and ai
others constant, which result from the flexion of the parts or
from the contraction of the muscles, becoming more marked
with age, and more or less numerous and profound as the
subject is inclined to leanness or to obesity.

The skin slides over the organs within certain variable

26 THE HUMAN BODY.

limits, according as the cellular tissue which it carries with
it is more or less relaxed, and as it is itself thick or thin.
Thus it is movable on the back of the hand and top of
the foot, on the front of the neck and on the surface of the
joints; it is almost immovable on the cranium, on the palm
of the hand, and on the sole of the foot.

Elastic, very extensible, and very resistant, it sustains,
without being torn, violent shocks and great compression; as
in certain wounds by firearms, for instance, the projectile
will penetrate the clothing to the skin, and injure the organs
which it covers without itself being broken.

The skin is the organ of feeling, its surface is endowed
with a sensibility which becomes extremely delicate at several
points. Being constantly in more or less intimate contact
with the atmosphere, it transmits to the economy the influ-
ence of external agents ; and it is partly by its tissues that the
fluids and gases are eliminated, which have done their office,
and are to be thrown off as the ultimate and abandoned
products of nutrition.

This function of continual exhalation makes the skin the
regulator of the temperature of the body. When the tern-,
perature of the organism is elevated either by motion or any
other internal or external cause, the sweat immediately
appears, and the cooling or loss of heat caused by its evapo-
ration reduces the temperature to its normal standard.
Lavoisier was the first who clearly explained this function,
so important from its utility, and from the serious conse-
quences which result from its disturbance.

Almost entirely deprived of the covering which nature has
given to animals, the colour of the human skin exhibits the
richest and greatest variety of shades. This colour is inces-
santly modified by the sensations, the movements, by moral
or physical emotions; and the transparency of its tissues
give as much delicacy as vigour to the tones which animate
it; it is not, as in the plumage of birds or in the shells of
molluscs, an assemblage of brilliant colours, often without
transition, but it is a blending at once the most harmonious
and the most striking; it is light in its softest changes, w
its most dazzling splendour.

THE SKIN — -EPIDERMIS.

21

On examining the thickness of the skin, we first find on
the surface a thin transparent membrane, a sort of organic
varnish, designed to receive the contact of the air and of
external objects. This is the epidermis. Elastic and very

Fig. io.— The Skin.

A. Section of skin under the microscope.

a b. Superficial and deep layers of epidermis.

c. Dermis — true skin.

(/. Fatty areas of the deeper portions of the dermis.

d. Muscular layer subjacent to t)ie skin.
t e' . Sweat glands and ducts.

f. Hair-follicle and sebaceous gland.

B. Hair seen under the microscope.

flexible, it lends itself to every movement of the skin, pro-
tecting its exquisite sensibility and modifying its property of
rapidly absorbing gases and soluble bodies. Although this
membrane is so thin, we can discover a superficial or
horny layer and two deeper layers. The first, the true
epidermis, thickens and becomes callous under the influence
of rubbing or pressure, as for instance on . the heel. The
other two layers are the mucous network of Malpighi and the
pigmentary layer. It is in the substance of this last especially
that the//£w/z/, the colouring matter of the skin, is developed.

22 THE HUMAN BODY.

It is a black or brownish substance, more or less abundant
according to the region of the body, individual, or race, but
constantly existing in normal conditions, alike in Europeans
and in the people of Soudan and Australia. The presence
of this pigment and its unequal distribution contribute to
the variety of complexion exhibited in the white race.

Under the pigmentary layer is the dermis, the thickest and
most resistant part of the skin ; it is white, semi-transparent,
and is composed of fibres of cellular tissue, fasciculated and
very dense; of elastic fibres, ramified and disposed in net-
work ; and of contractile fibre cells.

Immediately under the epidermis the surface of the dermis
is covered with papilla, little conical or rounded elevations
formed by the extremities of the nerves and vessels, which
are divided into nervous papillae and vascular papillae. Each
nervous papilla is surmounted by an organ, which from its
function and its microscopic dimensions is called a tactile
corpuscle or corpuscle of touch. They are much less numerous
than the other papillae, and are not found everywhere on the
skin. They are seen on the palm of the hand and on the
lateral and palmar surfaces of the fingers, on the sole of the
foot, on the tongue, the lips, and some other points. The
epidermis follows exactly the shape of these papillae, and
thus forms, in tracing the furrows which separate them, those
graceful meandering lines and elegant curves which we see
especially on the palm of the hand. Very dense at its thickest
portion, the structure of the dermis grows more relaxed on
approaching its lower face, and forms spaces or areolae in
which adipose tissue is developed, and at last it intimately
unites itself to the subcutaneous cellular tissue, from which
the dermis receives, and to which it sends, fibrous prolonga-
tions.

Gratiolet is inclined to admit that these so-called nervous
papillae are almost entirely wanting in nerves. He compares
them to little keys, so to speak, pressing lightly on a very
sensitive surface; and leaving there only very limited impres-
sions.

Other connections also exist between the tegument and
the subcutaneous cellular tissue: these are the nerves and

SWEAT-FOLLICLES — SEBACEOUS GLANDS. 23

the lymphatics and blood-vessels, which arise from the
skin or terminate in it ; and the follicles or glands, which are
situated in the substance of the dermis, according to most
authors, but in the subcutaneous adipose tissue, according to
Robin. These send the product of their secretions by
special ducts to the epidermis. These ducts traverse the
substance of the skin sometimes in straight and sometimes
in twisted lines, and give passage, some to hairs, to the
beard and to products of this nature which are formed in
the bulb of the hair-follicles ; and others, to the secretions of
the swsat-follicles and the sebaceous glands. The orifices of
the sweat-follicles, situated at the base of the papillae, exhale
the secretion in the form of insensible perspiration, or in
the form of little drops on the surface of the skin. Those
of the sebaceous glands open, some into the hair-ducts, and
others on the surface of the epidermis, and furnish to that
membrane and its dependencies a fatty substance which
seems to be designed to preserve the softness of the skin,
and to protect it from injury or change from the sweat; we
find them therefore in the greatest abundance at those
points where the transpiration is most active.

Of these glands and follicles of which the microscope
shows us the details, some attain the size of a grain of millet,
but most of them hardly reach a millimetre in diameter.
Their orifices are on the surface of the epidermis, a point
long disputed, but now admitted by anatomists. But these
orifices are not what were formerly denominated pores. It
was supposed that there were gaps or spaces in the skin
analogous to those in a sieve, and that the cutaneous secre-
tions issued from these gaps; but neither in the epidermis
nor in the skin are there any such gaps, and it will be seen
from the preceding description wherein the doctrines of the
ancients differ from, and wherein they resemble, those of our
own day.

The epidermis is regarded by anatomists as impermeable,
and yet experiment proves that even the perfect skin allows
gases and fluids to penetrate the organism. If we do not
admit that this absorption takes place through orifices at
the surface of the epidermis, and if we suppose it to take

24 THE HUMAN BODY.

place by imbibition or endosmosis, it is plain that the skin
is permeable, at least under certain conditions. But it is
not equally so throughout its whole extent; the thicker the
epidermis the slower and more difficult is the absorption ; in
short, the skin, like all the other tissues, absorbs certain sub-
stances to the exclusion of others.

We shall have occasion to discuss these phenomena in
treating of absorption.

After enveloping the body, the skin folds back upon the
openings which give access to its cavities, and modifying its
nature, becomes, under the name of the mucous membrane,
an internal skin, analogous, as we shall see further on, to
the external skin in its structure, its functions, and in the
intimate connection which is established by their reciprocal
influence and unity.

CHAPTER III.

Structure of the body. — Bones, cartilages, joints — Muscles, tendons,
aponeuroses.

Bones. — The bones are the framework of the human
body. They are formed of a hard and extremely resistant
tissue, and they surround more or less completely with
solid walls the cavities containing delicate organs; they
provide attachments and support for the soft parts, and
furnish a fulcrum for the movements of the body; and lastly,
by their resistance they permanently maintain the propor-
tions between its different parts.

The osseous substance is composed of calcareous salts —
phosphate or carbonate of lime — intimately combined with
organic principles, the decomposition of which produces
gelatine.

If the bone is immersed for a length of time in hydro-
chloric acid, the calcareous matter will be dissolved, and the
isolated gelatine will retain perfectly the form of the bone;
and in the same manner if the gelatine be destroyed by
combustion, the lime which remains will show the normal
form and dimensions of the bone. In a gelatinous state the
bone is soft and flexible; in the calcareous state it is hard,
rigid, and brittle ; in a normal condition each of these con-
stituent substances serves as a corrective to the other; and
their properties united give to bone its solidity and its
elastic resistance.

In the osseous tissues, as in all those of the body, we re-
cognize a movement of composition and of decomposition, of
molecules assimilated and again rejected after a certain time;
but in none of the organs so well as in the bones has it

26 THE HUMAN BODY.

been possible to demonstrate this double movement of nutri-
tion. If we mingle madder with the food of an animal, the
bones soon become red, and they regain their original colour
when the colouring matter ceases to form part of the food.
Or, more conclusive still, if the madder be given for a while
and then omitted, and after a time be again given, the bones
show a white layer between two red ones, which proves that
they grow from the circumference toward the centre, by the
ossification of the deepest layers of the periosteum.

The bones are divided according to their form into long,
flat, and short bones. The long bones, which are first and
most rapidly developed, are more dense in the middle or
body of the bone than at their extremities. This body is
formed principally of a compact bark or rind of ivory-like
tissue, and is pierced throughout its length by the medullary
canal; the extremities are composed of spongy tissue en-
veloped by a thin layer of ivory tissue. The long bones
combine to form the limbs and the thorax; designed to
serve as levers or columns, they are twisted on their axes or
bent so as to offer the greatest possible resistance in exert-
ing a force or supporting a weight.

The flat bones form the walls of the cavities of the
cranium, of the chest, and of the pelvis; they are thinner in
the middle than at the edges, and are composed of two
leaves or tables of ivory tissue resting upon and confounded
with each other at some points, and separated at others by
a layer of spongy tissue.

The short bones are very irregular in form and difficult to
describe; very spongy in texture and relatively light. They
develop later and more slowly than the others, and they are
placed in groups in parts of -the body where the bony frame
must possess a limited power of motion,- and yet be very
firm, as in the foot, in the hand, and in the spinal column.

There are 198 bones in the human skeleton when it has
reached its perfect development. On the surface of the
bones, and especially at the extremities of the long ones,
there are prolongations of different forms, designed either to
join the bones together, or to serve for the attachment and
insertion of muscles or ligaments. These prolongations are

Fig. it.— Skeleton.

EPIPHYSIS — PERIOSTEUM — CARTILAGE. 29

the apophyses, which are distinguished by anatomists by
names suggested by their position, by their use, or borrowed
from objects of which they recall more or less exactly the
form.

The body of the long bones and the central part of the
large bones are developed % before the extremities and the
edges. The extremities of the long bones are cartilaginous
in early life, their articulating surfaces are formed of cartilage
adherent to, but not continuous with, the bone to which it
belongs. This is the epiphysis, which afterward becomes
ossified, but is not perfectly united to the bone till about the
age of twenty. Some of the large bones also present epiphyses
on their edges or borders.

A white fibrous membrane, resistant in youth and reduced
to a thin layer of cellular tissue in the adult and aged, which
is called the periosteum, envelops every part of the bones,
except where they are covered with cartilage and where the
tendons and ligaments are attached. The periosteum adheres
closely to the bone, and distributes a network of vessels through
its substance. Recent surgical investigations have shown
that the periosteum plays an important part in the partial
reproduction of the bone after certain operations.

Cartilage. — To the bony system belong the cartilages,
which are formed of what might be termed tissue in a state
of transition between fibrous and bony substance. This
tissue, homogeneous in true cartilage, mingled with fibrous
substance in the fibre-cartilaginous parts, is elastic and flexible,
and in colour either yellowish or pearl-white. The cartilages
unite the bones at those points where, as in the chest, the
bony frame must yield to expansive movements; they furnish
a flexible skeleton to certain organs, as the external ear, for
example, the nose, the eyelids, and the larynx; and lastly, they
play an important part in the joints.

No part of the organism shows more clearly than the bony
system the care which nature has taken to provide during
infancy the gifts of which she is so prodigal in maturity, and
which she withdraws little by little in old age. During in-
fancy, when protected by maternal care and when the growth
should be rapid, the gelatine predominates in the bones;

30 THE HUMAN BODY.

they are flexible and have only a resistant power propor-
tionate to the movements and efforts of infancy; it is the
branch full of sap, but of which the woody portion is not
yet developed. In youth, as the muscular power augments,
the bones gradually become more solid; the extremities, at
first cartilaginous, become ossified; the epiphyses unite with
the body of the bone; and the articulating cartilages gain
more consistence. In the adult at last the bones are
complete. They are able to resist the muscular efforts of
maturity, and perform their functions perfectly, like all other
parts of the organism which are fully developed. But age
approaches, the strength decreases, nutrition falls off, the
bones become more solid, their power of resistance lessens,
the medullary canal enlarges, the proportion of calcareous
salts in the osseous substance augments, the bones are harder
but they are also more brittle. Thus, as each phenomenon
of life is linked with every other, we find the bones of a
child quickly and easily restored if broken; in the adult the
process may be longer, but is generally easy and complete;
in the old man the reunion of the fragments takes place
slowly, and sometimes cannot be effected at all. The deli-
cate twig, which afterwards became a vigorous branch, is
now dry and destined to speedy decomposition.

Joints. — The bones are attached to each other, either by
their extremities or their sides, in such a manner as to per-
mit freedom of motion to a greater or less extent between
the different parts of the skeleton and of the body. Held
together by a sort of cog-wheel system, by the fitting of a
projection into an appropriate cavity, or by juxtaposition,
they are maintained in connection either by the reciprocal
attachments of these projections, or by envelopes — the
articular capsules — and by ligaments, constant in their nature,
but varying in form and disposition, according to the dif-
ferent movements which they are designed to permit and
insure.

This assemblage, this connection of the bones, is termed
a joint. Joints are classed according to the form of the
articulating surfaces, and according to the extent and variety
of the movements produced by them. The bones of the

SUTURES — VARIETY OF FORM IN JOINTS. 31

skull are attached by the notches on their edges; these are
termed the sutures of the skull. They ossify with age, and
may be considered temporary joints, or rather a transition
between the separation of the bones and their unification.
The other joints, on the contrary, are permanent, and de-
signed to leave to the bones which they unite a mobility
which continues during life.

In some of the joints the surfaces are nearly plane or flat;
others present projections with corresponding depressions;
sometimes there is a segment of a spheroid upon which the
cavity which receives it moulds itself; sometimes a cylinder
which turns upon its axis in a ring, or a pulley-groove around
which slides an apophysis, or a mortise in which a tenon
is set.

Here, as in all the works of nature, we admire the inex-
haustible variety of form and of mechanism. Doubtless there
exists between certain articulations resemblances which per-
mit them to be classed together; but all are as distinct as
the bones which they unite, and like them present diversity
of character. Separately considered they astonish us no
less by the multiplicity of detail in their mechanism, whether
we examine the most complex or those whose surfaces pre-
sent the least irregularity. In fact we nowhere mid a uniform
plan, and the projections as well as the depressions are
curved in the most capricious manner.

These details of the general outline belong to no precise
geometrical form ; they are neither cubes nor spheres, neither
cylinders, cones, nor pyramids, although in anatomical
language these terms are applied to them. There is an assem-
blage in the same apophysis, or in the same cavity, of curved
surfaces borrowed from the most widely differing solids,
united under angles the most varied, and modelled on sinu-
osities which defy geometrical description.

In addition to these distinctive characters of the joints,
we may mention others which are common to them all. All
the joints have cartilages covering the bones which form
them; all are kept together by special ligaments, and are
lined with a sy no vial membrane, whose functions we shall
subsequently describe.

32 THE HUMAN BODY.

The polish on the articular cartilages facilitates their sliding
over each other, and lessens the friction of the bony ex-
tremities, while their elasticity diminishes the pressure and
deadens the shocks to which the joints are subject. The
thickness of these cartilages is proportioned to the motion
and the pressure which they are designed to support, and it
is greatest at the centre of the convexity of protuberances
and on the borders of cavities. The articular cartilages
never ossify, differing in this respect from those which, as in
the thorax for example, maintain continuity and play the
part of flexible bones. These last are ossifying cartilages.
The others differing in structure, being without vessels, have
been compared to the enamel on the teeth. In fact, they
are composed, like that enamel and some other analogous
productions, of an almost inorganic substance, and mechani-
cal injuries are the only ones which they have to fear.

Wherever in the organism surfaces move over each other,
they are covered with a membrane which secretes a fluid,
differing in quality according as there is a sliding or rubbing
of the organs. In the interior of the joints the membranes
are termed synovial membranes, and secrete a fluid called
synovia, because its physical characters resemble those of
the white of an egg. The synovia is to the joints what oil
is to the wheels of a machine; incessantly poured out upon
the surfaces, it lubricates them, and renders the movement,
already so easy owing to the polish of the cartilages, still
more so; it increases the suppleness and elasticity of these
last, which if they were not supplied with this oily fluid
would soon be worn out, and motion would be impossible.
This sometimes results from certain diseases, and sometimes
also in old age.

We have said that the joints are united by ligaments.
This term is applied to the bands or membranes com-
posed of fibrous tissue, flexible and inextensible. The liga-
ments, which are in the form of bands, are sometimes parallel
and sometimes interlaced, and placed either between the
articular surfaces or around them. In the latter case their
internal face is covered with intimately adherent synovial
membrane. The ligaments are attached to the bones at a

CAPSULAR LIGAMENTS.

33

greater or less distance from the articular cartilage, and they
adhere so strongly that it is easier to break the bone or the
ligament than to tear it from the spot where it is planted.
The membranous ligaments — capsulary ligaments or fibrous
capsules — are like a circular band of which the two openings
are fastened to the bones which they unite. The fibrous
pads or cushions which run round the circumference of cer-
tain articular cavities are also considered as ligaments.
They increase the depth of these cavities, and give greater

Fig. 12. — Elbow-joint.
A. H-umerus. B. Ulna. C. Radius.

solidity to their borders, upon which the osseous extremity
received there exerts considerable pressure.

Such is the assemblage of apparatus comprised in the
joints. The most perfect machine which man has ever been
able to construct bears no comparison to the admirable
mechanism of which we have just endeavoured to give a
general idea, in the precision, delicacy, and variety of their
organs or of their movements. Even in their most com-
plicated parts, machines invented by man offer nothing but

34 THE HUMAN .BODY.

a simple mathematical precision, impossible to mistake, be-
cause all the surfaces are conceived and traced out geometri-
cally. In the joints, on the contrary, all the lines and surfaces
.are vague and uncertain; and when we examine an articular
extremity, the inferior extremity of the humerus for example,
we shall at first be tempted to believe that the unsymmetrical
projections and depressions, the incomplete grooves, and the
undefmable irregularity of the whole, belong to a work
spoiled or modelled at hazard by a confused mind; but on
seeing the action of the elbow-joint when laid open by the
anatomist, we discover that it is to this very irregularity of
the bony extremities, to the multiplicity of detail, to the
absence of symmetry, and to the more or less limited extent
of their articulating surfaces, that the variety of movement is
due, and we cannot sufficiently admire this assemblage, so
complex, but yet so justly calculated to give to the move-
ments of the fore-arm the greatest precision, strength, and
rapidity, and to combine these movements with those of the
arm and the hand.

And if we pass from the most mobile of these joints to
those not at all or only slightly movable, the perfect coapta-
tion of their surfaces, their powerful methods of union, the
unity of movement of the bones, whether they take part in
the motion or serve only as fulcrums, all seem to be as
simple as possible in function, although the whole as well as
the details presents the most delicate application of the laws
of mechanics and statics. We may add that here as well as
everywhere in the study of the works of nature, we see the
organs develop themselves from the embryonic state to that
of perfection, under the influence and in the exercise of their
functions. . But leaving out the inimitable results produced
by life in natural creations, and considering them as inor-
ganic bodies, the mechanism of the joints leaves far behind
all the most ingenious productions of art or science.

The distance appears to us greater still when, instead of a
combination of surfaces and the method of their union, we
.study, the action of the muscles and the transformations
which are incessantly taking place in the organs of digestion
and. respiration. In unveiling a part of these mysteries to

MUSCLES.

35

man, the progress of science only increases his admiration.
What would it be if life, that force of which he is conscious,
and which he shares with all organized beings, should cease
to be to him an impenetrable secret!

Muscles. — United by the joints, the bones of the skeleton,
taken as a whole, approach the form of the body. But in
order to put these bones in motion,
and to bring these joints into play,
we must call to our aid an external
force. By itself, if we may be per-
mitted a very familiar comparison,
the skeleton is a puppet of which
the different parts are put in motion
by threads. The threads by which
the skeleton is moved are the
muscles. The name muscles is
given to the masses of red tissue
which constitute the flesh. We
have already described the ele-
ments of the muscular tissue; how
the primitive microscopic bundles,
united into secondary ones', become
muscular or fleshy fibres easily dis-
tinguished by the naked eye. These
fibres are parallel or divergent ac-
cording to the muscle, and assume
different forms. Sometimes it is
that of a ribbon (sartorius, sterno-
hyoid, &c.); sometimes a broad
web-like tissue of a texture more or
less firm, like the transverse muscles
of the abdomen; in one region the
muscle, swollen in the centre, and
drawn out like a thread at the ends,
resembles a spindle in form (biceps,
straight muscle of the thigh); in another it is fan-shaped
(temporal, obturator), or like a ring (orbicular muscle of
the lips and eyes) ; or the fibres converge like the radii of a
circle (the diaphragm); or are disposed in parallel lines like

Fig. 13. — Biceps muscle of the
arm.

A. Body of the muscle.
B. B. Superior tendons.
C. Inferior tendons.

36 THE HUMAN BODY.

the feathers of a pen (extensor muscles of fingers). Lastly,
certain organs, the heart for example, are nothing but
muscle, or rather an assemblage of muscles intimately
united.

The muscles determine the form and volume of the body,
and especially of the limbs. The outline depends upon their
projection, and changes incessantly as they are in action or
in repose. They are disposed in layers, deep or superficial,
and united in groups or separated by sheaths and mem-
branous partitions. Their colour varies from deep red to
pale rose, 'according to the region of the body they occupy,
age, sex, the constitution and richness of the blood. The
stronger the muscle the redder it is, and it becomes still
brighter under the influence of exercise.

The muscles of the human body number about 350, and
they are distinguished by names suggested by their form,
their locality, their functions, or their attachments. Some
are fixed to the skin, as several of the muscles of the face ;
others to muscles in their vicinity, as in the face and tongue;
others still to the cartilages, but the largest number to the
bones by means of the tendons or the aponeuroses, of which
we proceed to speak.

Tendons, aponeuroses. — In most of the muscles we can dis-
tinguish a fleshy portion, which is essentially the muscle, and
a fibrous portion, which is called either tendon or aponeurosis
according to its form. The tendons are fibrous cords of
variable length, rounded or flattened, of a pearl-white colour,
attached to the bones by one of their extremities and united
to muscular fibres by the other. The aponeuroses are
nothing but large thin tendons, a kind of fibrous web or band
which accompanies the muscles, separating them by partitions
or enveloping and uniting them in bundles. The tendinous
fibres are generally developed in the substance of the fleshy
part of the muscle, or on the surface, which they cover to a
certain extent. In the first instance they are inclosed, as it
were, by the muscle; in the second, they envelop it like a
sheath. This reciprocity gives great solidity to the whole.

The muscles and tendons are united together by the direct
adherence of the extremities of their fibres, which takes place

TENDONS, APONEUROSES.

37

in right lines ; or by the insertion of the fleshy fibres at some
point in the length of the tendon, at various angles, but never
exceeding 45 degrees. Such is the
force of this adhesion between the
two tissues that rarely if ever does
external violence or the greatest
effort succeed in overcoming it, the
tendon or the muscle breaks before
separating at their points of union.
We have already pointed out, in
speaking of the articular ligaments,
the remarkable fact that the adhe-
sion of two organic tissues is strong-
er than the cohesion of either of
the respective tissues.

The tendons and the aponeur-
oses, though very flexible, are en-
tirely inextensible, and offer there-
fore great resistance to force
applied to their length. This is
one of the conditions necessary for
the part which they play in uniting
the organ of motion and the object
to be moved.

Like the ossifying cartilages, the tendons may be considered
as a transition tissue. They partially ossify with age at their
points of insertion into the bones, but they are never entirely
transformed in the human race, as in some animals, the
Gallinaceae for example, into a bony trunk. Suppleness and
variety of movement would not accord with this transforma-
tion; and among the differential marks which Plato might
have added to his famous definition of man, this would have
sufficed to prevent Diogenes from saying, as he exhibited the
cock stripped of its feathers, "Behold Plato's man!"

A relatively slender tendon suffices to transmit a motive
force developed by a certain amount of contractile fibre, and
the fleshy portion of the muscles far surpasses in volume the
tendons and the aponeuroses. If the muscular fibres attached
themselves directly to the bones the surface of the bones

Fig. 14. — Lower portion
of the leg.

A. Tendon of Achilles.

38 THE HUMAN BODY.

would not be sufficient to supply space for them ; this direct
attachment to large surfaces is confined to a few only, the
others being attached by their aponeuroses or tendons to
limited spaces.

The muscles are at the same time contractile and exten-
sible. The muscle shortens by contraction and increases
in thickness at the same time that its' length diminishes; in
.repose it is soft and yielding to touch, in contracting it
becomes hard and resistant. These successive changes are
easily demonstrated by applying the hand to the course, of
a superficial muscle, on the front of the arm for example, on
the biceps. When the fore-arm is extended it projects but
slightly and yields to pressure; it swells, on the contrary,
becomes resistant, and forms a marked protuberance, when
contracting in order to flex the fore-arm.

The contraction of a muscle may also take place without
its being shortened. When, for example, the fore-arm is
extended upon the arm, if the extensors oppose the flexion
by contracting, the biceps and anterior brachial, both flexor-
muscles, may contract without their ends approaching each
other.

Glisson, Borelli, and other anatomists have supposed that
the muscle increases in volume during contraction; but further
experiment, confirmed also by those of Provost and Dumas,
has demonstrated that it gains in thickness only what it loses
in length, and that there is no change in the absolute volume.

In contracting, the muscular fibres become tortuous and
wavy, wrinkles are formed on the surface, a sort of trembling
pervades the whole mass, and its temperature is raised.
Becquerel and Breschet have observed this increase to reach
half a degree centigrade.

To the contraction of certain muscles must correspond
the inertia or even lengthening of the antagonistic muscles,
as for instance when the fore-arm is flexed upon the arm or
the leg upon the thigh, the extensors of the fore-arm and of
the leg take part in the movement and lengthen by means
of their extensibility. In like manner the muscular texture
which forms the walls of certain organs, as of the stomach and
intestines, is expanded by the fluids and the aliments, or by

MUSCLES, THEIR ACTION. 39

the gases which are developed in them. The flute-player of
antiquity kept his cheeks distended by means of a leather
strap. Thus there is a constant struggle between the con-
tractility and the extensibility of the muscles. But if, during
the contraction of certain muscles, as the flexors of the arm,
the antagonistic muscles, the extensors, are relaxed and do
not oppose the movement, they regulate it nevertheless by
virtue of a property named muscular tonicity, which gives to
their tissues even when not contracted a certain power of
resistance. Thus when a group of muscles is paralyzed, the
antagonistic muscles cause by their contraction a jerking
movement which has no regularity.

In contracting, the muscles act like levers upon the. bones,
and therefore just so much less powerfully as they are placed
obliquely to the bone. Notwithstanding the larger part of
the muscles are attached to the bones at an acute angle, and
their direction is very oblique in regard to the lever they
are to move. The result is a great loss of force, but this
loss is compensated by an increase of volume in the muscles,
that is in the number of fibres of which they are composed.

Most of the muscles are subject also to deviations or
reflections around the joints. Some even take a direction
perpendicular to their original one in turning round bony
hooks or in the grooves of the pulleys. The apophyses, or
the protuberances to which they are attached, permit them
to move at a greater angle and a more favourable one than
the initial angle, and this angle gradually increases as the
bone obeys the force applied to it; and lastly, the relative
direction of the muscle as regards the bone varies according
to the attitude. These dispositions of the muscles are always
adapted to the kind of movement to be executed, to the
extent or rapidity required, or to the force demanded; and
they are always so combined as to produce the maximum of
useful result. So in flexing the fore-arm, in elevating the
arm, the bones act as levers of the third order. The biceps,
anterior brachial, and deltoid muscles act as very short
levers upon the arm, and their initial direction is almost
parallel to the bone, but it soon becomes almost perpen-
dicular to it. In this case extent and rapidity of movement

40 THE HUMAN BODY.

are important, force is only a secondary consideration. If
we wish to raise the body on the toes, motion is more limited
but a great amount of force is necessary. The gastrocnemius
and soleus muscles, which form the calf of the leg, are inserted
by the tendon of Achilles — the largest in the body — to the
posterior extremity of the calcaneum (or heel-bone), and
perpendicular to its axis ; the posterior tibial muscle and the
flexors of the toes pass behind the internal malleolus under
the calcaneum and under the astragalus, as in the groove of
a pulley, and are inserted into the plantar surface of the
scaphoid and to the last phalanges of the toes, and these
muscles act upon the foot, which serves as a lever of the
second order; that is to say, under conditions the most
favourable to the power represented by the muscular con-
traction.

CHAPTER IV.

Spinal column. — Thorax. — Upper limb ; shoulder ; arm, fore-arm,
hand. — Lower limb; hip, thigh , leg, foot.

Spinal column. — The spinal column is the foundation to
which all the other parts of the skeleton are adapted. It is
composed of seven cervical vertebrae, twelve dorsal and five
lumbar vertebrae, and is terminated by the sacrum and
coccyx. Throughout its whole length runs the vertebral
canal, which holds the spinal marrow, and communicates
with the cavity of the skull. Each vertebra is composed of
a body, two articular processes, two transverse processes, and
a spinous process. The body, the anterior portion of the
vertebra, is cylindrical, and forms a layer of the column.
The articular processes, placed at the sides, serve to unite the
vertebrae together; and \hetransverseprocesses give attachment
to the ligaments, muscles, and in the dorsal regions to the
ribs. The spinous process, the posterior portion of the verte-
bra, forms that series of projections which has given to the
vertebral column the name of the spine. The spinous process
bifurcates into two plates which complete the ring or verte-
bral orifice formed by each vertebra, and the open space in
which forms a segment of the vertebral canal. Numerous
and powerful ligaments combine to unite the vertebrae. Be-
tween their bodies fibrous disks in the form of lentils are
placed, which adhere intimately to the articular surfaces ;
they are formed of concentric layers, and near the centre
there is a spongy substance saturated with a fluid analogous
to the synovia. These disks or intervertebral ligaments,
besides binding together the bodies of the vertebrae, serve

42 THE HUMAN BODY.

to diminish the shocks and the pressure to which they are
subjected from the weight of the parts of the trunk above
them. They sink down and become thinner while the body
is erect, so that there is a difference in the height between
morning and evening of about "02 or '03 of a millimetre;
but repose in bed restores to the fibrous disks their primi-
tive thickness.

Between the vertebral plates stretch the yellow ligaments,
remarkable for being formed of an elastic tissue which yields
to the movements of the spinal column. Other inextensible
ligaments envelop the spine at every point, and give great
solidity to the whole. The spinal column has three curves —
two backward in the cervical and lumbar regions, and one
forward in the dorsal region. The ligaments which unite its
layers permit only a slight degree of flexibility in the upper
dorsal region, but this is a little more extended at the neck
and loins, and powerful muscles give it at need great rigidity.
And lastly, to its curves, and to the complicated mechanism
of its articulations, it owes its great power of vertical re-
sistance.

The head is balanced upon the first cervical vertebra,
which is called the atlas; the manner of its articulation with
the spinal column permits great extent and freedom of move-
ment, while powerful ligaments and muscles give it great
strength.

Thorax. — The ribs are attached by the transverse pro-
cesses to the dorsal vertebrae, and in front by cartilages to
the sternum or breast-bone. They are twelve in number on
each side. The interstices of this bony cage are filled with
muscles ; they cover and form with it the walls of the chest,
called also the thorax or thoracic cavity, which contains the
lungs and heart. The flexibility of the costal cartilages, and
the mobility of the articulations of the ribs with the spinal
column, allow the thorax to expand and to -contract in re-
spiration.

Upper limb. — Near the apex of the cone formed by the
chest the upper or thoracic limbs are attached. They are
composed of four parts — the shoulder, arm, fore-arm, and
hand. The two bones of the shoulder are the scapula^ which

SHOULDER-JOINT, ELBOW-JOINT. 43

is attached by muscles to the upper part of the back, and
the clavicle or collar-bone, which extends from the sternum
to the scapula, embracing the top of the chest. At the
angle formed by the superior border and the external edge
of the scapula an articular surface, called the glenoid cavity,
receives the upper extremity or head of the humerus, the
bone of the arm, which articulates at the elbow with the
ulna and the radius, the two bones of the fore-arm; these
form with the carpus the wrist-joint, which unites the fore-
arm to the hand. The deltoid, the great dorsal and great
pectoral, and other less powerful muscles, combine to form
the shoulder, and give motion to the humerus. The triceps
and biceps of the arm, &c., which surround the humerus,
flex or extend the fore-arm and turn it on its axis; and
numerous muscles cover the fore-arm and move the hand.

The articulation of the humerus with the scapula or the
shoulder-joint is, of all joints, the one that permits the most
extended movement. The shallowness of the glenoid cavity
permits great freedom of motion to the rounded head of the
humerus. Thus the arm, which hangs parallel with the body
in a state of repose, can be raised vertically to the head,
laterally forward so as almost to enfold the chest, and also
backward, though in a more limited degree; it can be turned
on its axis in all these positions, and in the movement of
circumduction it describes a very flat cone, the base of
which, especially in front, approaches the apex.

The elbow-joint is one of the most complicated in the
whole system. The lower extremity of the humerus, and the
upper extremities of the ulna and the radius, are adapted to,
and interlock with each other by a series of rounded surfaces
and pulley -grooves, which permit the fore-arm to flex itself
forwards upon the arm; while a protuberance of the ulna, the
olecranon, which forms the projecting part of the elbow, limits
the backward movement by resting in a cavity of the humerus.
It is into the olecranon that the tendon of the triceps of the
arm, the principal extensor of the fore-arm, is inserted, and
we shall see the analogy farther on between this process and
the knee-pan.

The movements of the fore-arm singularly multiply by

44 THE HUMAN BODY.

their application those of the arm. The radius and ulna
may be placed in contact with the humerus by flexion, and
again the radius turns on its own axis, without either the
ulna or the humerus taking part in this movement, which is
called pronation or supination, according as the palm of the
hand is turned outward or inward.

But what renders the thoracic limb a perfect organ, that
which explains the variety and extent of its movements, and
which gives them all their value, is the hand ; that admirable
instrument which in its perfection belongs only to the human
race.

The hand is elegant and beautiful in form. Its isolation,
its contour — defined without stiffness — the delicacy of its
mould, the mobility of its different parts, and the variety in
their tints, make of it a being by itself in the human body,
and give it an expression and a physiognomy. Completely
developed even in infancy, it presents a most attractive
model and an inexhaustible subject of study to the artist.
Its structure has led many philosophers to think that it is to
it alone that man owes his superiority to the animals, and to
attribute to it the greatest influence over the intellectual
faculties. But the study of man shows that we must reverse
this proposition. The hand is only the instrument of the
intellect, the perfection of the one is necessarily dependent
upon that of the other, and the hand of man, like every
other part of his being, has no equal in the animal kingdom.

As for seeing in the greater or less perfection of the hand
a sign of the degree of intelligence, and carrying it so far as
to distinguish between the hand of a man of talent and
genius, and that of a fool or a man of moderate ability — this
is a theory which, speciously presented, might perhaps be
entertained as a subject having curious aspects, but on no
other ground. In short, if the hand of the idiot is alike
badly developed with the brain — if we believe that an arrested
development of the fingers, or the presence of supernumerary
ones, are signs of degeneration in the race — are we to con-
clude that perfection of the thoracic limbs is the rule, as has
been said, in men of eminence? We need not go so far
back as Esop for an example of a great mind in a deformed

THE HAND — WRIST-JOINT. 45

body. Concte, Luxembourg, Pope, and other illustrious and
celebrated men, were victims of rickets. They had long and
knotty hands, one of the most constant signs of this malady.
If men of inferior intelligence often have thick and inflexible
hands, it is because they are often born under conditions which
impose rough work upon them. They receive as a heritage,
with the toil of their fathers, this clumsiness of form, which is
the consequence of this toil. The hand of the man who is
not forced by his position to manual labour is always finer
and more delicate than that of the workman, and he trans-
mits to his children this detail of conformation as well as the
general resemblance. The delicacy of the limbs, the prin-
cipal element of their elegance, is therefore a sign of race
rather than of intelligence, and belongs especially to the
oriental. The hand of a European cannot enter the guard
of an Indian sword or poniard. Shall we conclude from
that that the Anglo-Saxon or the Norman has less intelligence
than the Arab or the Hindoo? De Blainville relates that
Re'camier attached a certain importance to the form of the
hand, and was accustomed to examine those of his pupils
with this idea. "Mine," he adds, "were, like the others, sub-
mitted to the inspection of the master, and the result was not
unfavourable to me." Re'camier being present, confirmed
the statement of the former pupil of the Hotel-Dieu, now
become an eminent naturalist. But the hand of De Blain-
ville was neither fine nor elegant; it was a well-made,
vigorous, and muscular hand, like the body to which it
belonged; equally skilful, in fact, in holding a sword, a
pencil, or a scalpel.

The wrist-joint, which unites the hand to the fore-arm,
resembles in its mechanism that of the shoulder. Eight
bones of different and very complicated forms constitute the
wrist or carpus. Three of these form the articulation with
the fore-arm, the others are united to the five bones of the
metacarpus^ the palm, or middle part of the hand, to which
the fingers are attached. These are composed of two pha-
langes in the thumb, three in the index, middle, ring, and
little fingers. The first three bones of the carpus are grouped
in such a manner as to present an ellipsoid surface on the

46

THE HUMAN BODY.

side of the fore-arm; a condyle which is received by the
elliptic cavity formed by the inferior extremity of the radius
and ulna. The hemispheric head of the humerus turns oh
its axis in the glenoid cavity, but this movement is prevented
in the hand by the elongated form of the condyle of the
carpus. The rotation of the ulna supplies this want, and the
hand turns with the bones which are attached to it in

Fig. 15. — The hand, palmar aspect.

A. Short abductor muscle of tlie thumb,
above and outside of ivliich is seen
the opposing muscle (opponenspollicis].

B. Slwrtjlexor of thujnb.

C C. Tendons of the superficial flexor

of the fingers.
D. Sheath of the tendons.
E E. Tendons of the deep flexor.

Fig. 1 6. — The hand, dorsal aspect.
A. Annular ligament of the inrist.
B B. Tendons of the common extensor

of the fingers.
C C. Tendinous expansions fastening

tlie tendons together.

supination and pronation. Further, it has a separate move-
ment in flexing the hand forward, backward, or sidewise.
In circumduction it describes a cone, and makes many
other movements in common or singly.

The numerous muscles which determine these movements
form a very complicated mechanism. Their tendons are

ACTIONS OF THE HAND. 47

interlaced and bound together by bands and aponeurotic
fibres, and from this results a more or less complete unity of
action. It is sometimes difficult to make a movement with
a single finger without the others taking part in it, as in
executing instrumental music, for instance ; but practice gives
to these movements perfect independence. The mechanism
of the movements of the hand has been made singularly clear
by the recent experiments of M. Duchenne of Boulogne, who
has succeeded in distinguishing by means of electricity, the
action not only of different orders of muscles, but also of
each particular one. Gerdy counts thirty-four distinct move-
ments of the hand, and if we include the combinations of
these different movements we shall reach a much higher
number. The opposition of the thumb to the other fingers,
alone or united, is of all these movements that which
especially characterizes the human hand, in which alone it
exists in its perfection. This action of the thumb results
from its length, from the first metacarpal bone not being
placed on the same plane as the other four, as is the case in
the monkey, and from the action of a muscle — the long
flexor of the thumb — peculiar to the human hand. This
muscle completes the action of the other motor of the
thumb, and permits man to hold a pen, a graver, or a needle ;
it gives to his hand the dexterity necessary in the execution
of the most delicate work; it is the attribute of his intelli-
gence. In repose the hand of man is presented in an
attitude half opposed to the thumb; but it is not so in the
monkey, even in the species most resembling man. It is
opposable in these animals, but much less so than in man;
and the five bones of the metacarpus being on the same
plane, the fingers — or toes — can be placed flat upon the
ground in walking, in which the four limbs always take part.
Properly speaking, then, the hand belongs to man alone, and
its conformation does not permit us to consider it as a nor-
mal organ of locomotion. It can by turns form itself into a
plane, round itself into a cylinder, hollow itself into a gutter^
make the fingers spread like so many diverging rays, and
form, in the words of De Blainville, a compass with five
branches; it collects the fingers in the form of a cone, of a

48 THE HUMAN BODY.

spheroid, &c.; and lastly, it can reach every portion of the
body.

The hand is essentially the organ of touch and of prehen-
sion. These functions devolve principally upon its anterior
or palmar face. The nervous papillae with which it is pro-
vided abound specially at the ends of the fingers, where they
form furrows in elegant curves under the epidermis. The
tendons in it are very numerous, and bound together by
multiplied connections. Strong aponeuroses and sheaths,
through which the tendons slide, make the skin compact, and
combine to give unity to the general movements of the dif-
ferent parts of the organ, and independence to partial ones.
A layer of adipose tissue, very close in texture, protects, with-
out lessening its power or its delicacy, that network of
muscles, vessels, and nerves, this apparatus which sometimes
barely touches an object, and sometimes grasps it with such
violent pressure. The hand, in fact, is either a delicate
pincer or a powerful vice; it guides the burin of the en-
graver, which leaves behind it the finest trace, the hatchet
of the carpenter and the axe of the woodman, whose blows
are given with as much strength as skill. The fingers of the
sailor knot the heavy cordage, and those of the optician
stretch a spider's thread, without breaking it, across the field
of an astronomical telescope. The same organ can hold a
switch, a club, a sword, a hammer, or a pen. It moulds
itself to a body to ascertain its form ; it comes to the aid of
the eye in completing or rectifying its impressions, and in
some cases even supplies its place. Thus the finger of the
physician perceives on the surface of an organ the slightest
inequality in relief; and the hand of Michael Angelo fol-
lowed with enthusiasm the contour of the antique torso,
which the eyes of the great artist could no longer contem-
plate.

But nothing gives a more complete idea of the perfection
of the mechanism of the hand, than the execution of instru-
mental music. Examine an artist while he plays on a violin.
His fingers rest upon the strings so as to leave them exactly
of the length necessary for the tones they are to give. The
half of a millimetre, more or less, greatly changes the true-

ACTIONS OF THE HAND. 49

ness of the note; and a cord a millimetre out of place pro-
duces a note which even the unpractised ear recognizes as
false. But the fingers fall upon the strings at precisely the
point required. They run over them, succeeding each other
with giddy rapidity, following every imaginable combination,
and yet the hand gliding over the instrument incessantly
changes its position. Sometimes a single finger produces an
isolated note; sometimes two or three act simultaneously to
produce a concord; while a fourth, striking the string with
increasing rapidity, produces a trill which rivals that of the
nightingale. And even this is not all. The other hand
holds the bow, and the movements of the right arm must be
in correspondence with those of the left hand; the coincid-
ence between the movements of one hand and that of the
other must be mathematically exact. Add to these all the
modifications necessary to produce the piano and the forte,
to swell the sound or to let it die away — all, in a word, that
constitutes musical expression, and it will be admitted that
this mechanism is allied to the wonderful, and that it sur-
passes the most perfect productions of human art.

The agility and flexibility of the hands, the concordance
and independence of their movements, is not less remarkable
in the playing of the pianist. How is it possible not to ad-
mire those two hands, both oftenest occupied together, and
the action of which alternates or coincides with so much pre-
cision and rapidity; together they produce on an average from
six to eight notes at a time — separating, approaching, crossing,
and mingling their fingers, which move over the keys as if each
one were completely independent of all the others? A skil-
ful pianist produces about 640 notes a minute in medium
time, and 960 in extremely quick time. These numbers
give us an idea of the rapidity of movement which can be
attained by the hand of man.

The devoted servant of the body, the hand which nourishes
it knows also how to defend it. It has been said that man
is created without arms. What then is the hand which en-
ables him to construct and employ for his defence those in-
genious and terrible machines, that hand which can at need
itself become a formidable weapon? The poets have sung

4

So THE HUMAN BODY.

the praises of Pollux defending his own life and that of his
companions with the arms which nature gave him ; but if we
admire Pollux battling with the Sicilian giant, we turn our
eyes from the arena ensanguined by the gauntlet of Enteilus.
The soldier considers it an honour to employ with skill in
the defence of his country the sword which she has intrusted
to him; but he despises the arms and the trade of the
gladiator.

The principal function of the upper limb is to remove
objects from the body, and to draw them to it; but it can
also remove the body from a fixed point, or approach it to
one. It is in this way that the sailor raises himself on the
rigging, or the gymnast on the trapeze ; but the weight of the
body is not in proportion to the strength of the limbs which
raise it, and although exercise renders this effort less difficult
by increasing the power of the muscles, it is evident that
here the arm performs a function which does not devolve
upon it chiefly, and which belongs to a more powerful mem-
ber, of which we will now speak.

Lower or abdominal limb. — It is composed, like the upper
limb, of four parts — the hip, thigh, leg, and foot. The two
bones of the hip, or pelvic bones, articulate together and with
the sacrum; this last, placed between the two like a wedge,
transmits by their means the weight of the body to the lower
limbs, which are the pillars of the human edifice. On the
external face of each pelvic bone we see a deep, hemispheri-
cal, articular cavity. This is the cotyloid cavity, which receives
the head of the thigh-bone, and forms with it the articulation
of the hip. The femur or thigh-bone is the longest and
strongest bone in the skeleton ; it is almost cylindrical, and
is curved outward, which gives it greater strength. At its
upper extremity we see the head of the femur, supported by
a neck which is united to the body of the bone at an ob-
tuse "angle.' This obliquity has the effect of increasing the
distance between the two femurs, and in consequence be-
tween the two lower extremities, thus giving to the body a
larger base and greater stability. Another result is, that the
weight of the. body is transferred to the femur, but not
directly and in a right line; the necks of the two femurs

HIP-JOINT, KNEE-JOINT. 5!

form by their union part of an arch upon which rests the
upper portion of the cotyloid cavity, and thus divides the
force acting upon the lower limbs.

The head of the femur represents nearly two-thirds of a
sphere. It exactly fills the cotyloid cavity, but is not itself
all inclosed in it, as the depth of the cavity does not exceed
half the diameter of the sphere to which it belongs. A very
elastic, circular, fibro-cartilaginous ring surrounds the edge
of the cotyloid cavity, increasing its size, embracing the head
of the femur; and acts as a valve and hermetically closes the
articular cavity in which the head of the femur is retained by
atmospheric pressure alone. In fact, if we place this articu-
lation, properly prepared, under the receiver of an air-pump,
we shall see, as a vacuum is produced, the head of the
femur gradually slip down and leave the cotyloid cavity as
far as the ligaments will permit, and when air is again ad-
mitted into the receiver, it resumes its place in the cavity.
This beautiful experiment of E. Weber shows in a striking
manner the direct and constant influence of external agents
on the functions of the organism.

The inclosing of the head of the femur in the cotyloid
cavity gives the articulation of the hip great solidity, which
is augmented by the muscles and ligaments which hold the
parts together as well as give them motion, so that it is only
by the greatest violence that the head of the femur can be
forced out of this cavity. This articulation, which is of the
same nature as that of the shoulder, permits the movement
of the lower limb in every direction, though to a less ex-
tent than that of the arm. We shall again have occasion to
discuss this movement.

The lower extremity of the femur ends in two oblong,
rounded masses, which are called the condyles of the femur,
which rest in two cavities in the superior portion of the princi-
pal bone of the leg, or tibia, and form with them the articula-
tion of the knee. The semi-lunar cartilages, in terposed between
the two bones, diminish the pressure of the femur on the
tibia, and prevent the displacement of the former by increas-
ing the surface and depth of the articular cavity. In front
of the knee-joint is placed fas patella or knee-pan, the largest

S3 THE HUMAN BODY.

of the sesamoid bones, which adapts itself by two articular
facets to those presented by the condyles of the femur, and
gives attachment by its upper border to the tendon of the
extensors of the leg, while by its lower border it is intimately
united to the ligament of the knee-pan, which fastens it to
the tibia. In comparing the elbow with the knee, we per-
ceive the striking similarity of the knee-pan to the olecranon.
The knee-pan serves as a pulley for the extensor-muscles, the
action of which upon the leg is increased by the change of
direction given to them, while the olecranon is a powerful
lever, by means of which the fore-arm is extended.

Fig. 17. — Knee-joint.

Front view. Side view.

A. Femur. A. Femur.

D, t>. Condyles of femur. B. Knee-pan.

d. Upper extremity of fibula. C. Tibia.

C. Tibia. D. Fibula.

D. Fibula.

The second bone of the leg is \hefibula, which is parallel
to the tibia, and with it forms the articulation of the foot.
This bone, which takes no part in the articulation of the
knee, yet represents the ulna, which plays so important a
part in the formation of the elbow, while the tibia corre-

ANKLE-JOINT. 53

spends to the radius. Nature, by one of those transforma-
tions of which she furnishes numerous examples, has united
the two extremities of the ulna and radius in one, allowing
the first of these bones to exist only as a rudiment in its upper
portion. This blending of two organs is termed by naturalists
a coalescence. The resemblance of the tibia to the radius
was remarked by De Blainville, and has been demonstrated
by M. Martins in his beautiful work on the pelvic and
thoracic limbs.

The lower extremities of the tibia and fibula united form
a mortise, in which the astragalus, one of the bones of the
tarsus, is received, and thus constitute the tibio-tarsal articula-
tion, or articulation of the foot. The foot moves upon the leg
in such a manner as to form with it a straight line when
extended. The movement in an opposite direction, or flexion,
is much more limited, the two mallcoli which embrace the
astragalus not permitting lateral movements in the foot, those
which do take place being made by the articulation of the
astragalus with the other parts of the tarsus, though a limited
movement of circumduction can be made by the foot.

It has been said that the foot is another hand — -pes alter a
manus — and if the hand completes the arm, so does the foot
complete the leg. Without it locomotion could not be
effected except by movements quite different from those of
walking, and under conditions of equilibrium much less
favourable, and with much greater fatigue; running, and
consequently jumping, would be impossible. But if the foot
and the hand are varieties of the same type of organization,
they present differences in regard to their respective uses;
the foot, designed to support the body, is especially remark-
able for its solidity; in the hand mobility is the predomi-
nating quality.

The foot of man, exclusively designed for the support of
the body, is not an organ of prehension, and cannot, like the
foot of the monkey, take hold of objects by opposing the
thumb to the other fingers ; the toes, disposed upon the same
plane, have neither the length of the fingers nor the extent
and variety of their movements; in a word, it is a foot and
not a hand, as it is in the quadrumana.

54

THE HUMAN BODY.

The foot is composed of twenty-six bones, seven of which
constitute the tarsus, which articulates with the leg and

Fig. 18. — Skeleton of the foot.

A. Internal malleolus, lower ex tr em- E. Cuboid,
ity of tibia.

B. Astragalus.

C. Calcaneum.

D. Scaphoid.

F. First metatarsal.

G, H. First and second phalanx of the
great toe.

corresponds to the carpus. Five bones form the metatarsus,
which corresponds to the metacarpus, and articulates with
the tarsus behind and with the toes in front. The foot is
narrow and thick in its posterior part, thinner and broader
anteriorly ; it forms a right angle with the leg, and rests upon
the ground at the extremities only. The middle portion is
in the form of an arch, and in consequence resists shocks
and supports pressure much better than it could if it were
flat and touched the ground throughout its whole length.
And although the parts are very firmly united together, there
is sufficient mobility to give great elasticity to the whole, and
this elasticity is augmented by the toes. The foot thus
supports the weight of the body like an arch and spring
combined, giving it in this way great advantage in resistance.
And lastly, in jumping from a height it extends itself
instinctively, and touches the earth first at its point only, so
as to break the shock. This distribution of force, which
results from the form and the elasticity of the foot, not only

UPPER AND LOWER LIMBS.

55

protects its mechanism, but also avoids the grave injuries
which might be produced in certain organs, such as the brain
and the liver, by the rebound.

Fig. 19.— The foot.

If we compare the upper and the lower limbs taken as a
whole, we shall remark among their principal distinguishing
characteristics, that the flexion of the fore-arm upon the arm
takes place in a forward direction, while that of the leg is
backward. M. Martins has demonstrated that this opposi-
tion in their movements, necessitated by their destination to
different functions, is due to the twisting of the humerus.
The femur is a straight bone and not twisted upon its axis.
The humerus, on the contrary, is turned on itself 180°, or
half the circumference. This is not the result of the me-
chanical action of the muscles and of the function of the
upper limb ; although the form of the bone does not permit
this peculiarity to be anatomically recognized till about the
second year, it exists virtually as soon as the bone is
developed. Muscles, vessels, and nerves all follow this
rotating movement indicated by the spiral disposition of the
humerus, and most anatomists have pointed it out without
hinting at the physiological consequences which M. Martins
has shown result from it. This learned observer has shown
that the humerus, artificially untwisted, corresponds in all
points with the femur of the same side, and by this manoeuvre

56 THE HUMAN BODY.

in an opposite direction to the work of nature, he has
explained the proceeding by which she bent the articulation
of the elbow forward and that of the knee backward.

The articulations of the lower limb permit to it a great
variety and extent of movement. Under the action of
powerful muscles it folds back upon itself or becomes a
rigid column, raising or lowering with rapidity and facility
the body of which it supports the weight. In walking it is
carried forward or backward, and by turns extended or bent;
it turns on its axis or changes from the vertical in order to
maintain the equilibrium by the direction of the foot or to
enlarge the base of support. It can raise itself laterally almost
to a right angle with the body, and in front it approaches it
still more nearly. In fencing it bends or is extended, raises
and lowers the body, and carries it backward and forward by
movements which succeed each other almost as rapidly as
those of the arms. But it is especially in the varying steps
of a skilful dancer that we can admire the perfection of this
mechanism, and all the suppleness, strength, and agility that
exercise can give to it.

CHAPTER V.

Motion. — Effort. — Locomotion; standing, walking, running, jumping,
swimming.

Motion. — Physiologists remark several varieties of motion
which may be grouped in two — voluntary and involuntary
movements. Among the involuntary movements, which ars
also called automatic, some result from the impression pro-
duced by an idea, a passion, or a scene, gay or sad, or by a
movement identical with that which is produced. Such art,
laughing, and the motions of the face expressing sadness,
anger, fear, and other moral or physical impressions; trem>
bling of the limbs in consequence of deep emotion, yawning,
and so forth. Others proceed from the excitement of ths,
sensitive nerves, such as sneezing, coughing, winking, chat-
tering of the teeth, or shivering after a cold bath.

In certain cases, in fact, impressions transmitted from th&
organs to the brain, either directly by the nerves of sensa-
tion or indirectly by the spinal cord, without any sensation
taking place, or what amounts to the same thing, without
our being conscious of any, occasion an excitement which is
transmitted to the motor-nerves, and causes movements in
which the will has no part. These movements are generally
executed by the muscles of organic life, which are not
under the control of the will ; but they can also be made by
those which are under its control. These are called reflex
movements. Some of them are undoubtedly automatic; as
for the others, it has not been demonstrated that a sensation
and an act of the will do not precede the muscular contrac-
tion. Thus sneezing and coughing are independent of the

58 THE HUMAN BODY.

will, it can neither prevent them nor arrest their develop-
ment. It is the same with the chattering of the teeth, with
shivering and winking of the eyelids on contact with the air,
with the tears, or only when a foreign body menaces the eye.
In this last case, although the muscular contraction is in-
stantaneous and seems to be involuntary, it is evidently pre-
ceded by a sensation which the eye has transmitted to the
brain. This may even be considered as voluntary, since if
the attention is excited, the will can oppose the instinctive
movement.

Other movements take place in the organism of which we
have more or less perception; when a carriage threatens to
overset, for example, we throw ourselves to the side opposite
the inclination ; or when suddenly coming on the edge of a
precipice the body stiffens or is thrown backward; and when
a player at ball or billiards inclines or turns in the same direc-
tion in which he wishes to direct his ball. Analogous
phenomena are caused by a sort of attraction or instinctive
imitation. When, for example, the eyes follow the move-
ment of a great waterfall into a gulf, the body very soon fol-
lows the oscillations, though we do not perceive them until
the motion becomes so great as to threaten to drag us into
the abyss. We are indebted to M. Chevreul for the obser-
vation and explanation of effects of this nature, of which
charlatanism avails itself in table-turning. If the elbow be
placed upon a table, and a pendulum formed of a string and
a ring be held in the hand, and we fix the eyes on the ring,
we shall soon see it begin to oscillate, although the arm ap-
parently remains immovable; the oscillations may keep the
same direction, or change according to the mental desire,
and this without any bad faith or a consenting movement on
the part of the person holding the pendulum. But if we
place a support under the hand near the end of the fingers,
or a bandage over the eyes of the experimenter, the oscilla-
tions cease. They were caused by an almost imperceptible
and involuntary movement of the fore-arm and hand, under
the influence of the eyes looking at the ring and the direc-
tion that it takes. And again it is a similar movement or
series of movements which gives the impulse to the turning

VOLUNTARY MOTION EFFORT. 59

table; in the unconsciousness of the muscular contraction
lies all the merit of this phenomenon, which loses its mar-
vellous character as soon as you show the too credulous per-
formers that they themselves are the involuntary movers.

Voluntary movements, as their name indicates, are produced
under the influence of the will, but not under its direct or
immediate action. The volition of the movements of loco-
motion, for example, emanate from a certain part of the
brain, from the cerebral lobes; but in order that the move-
ment may be executed, the muscles must contract, and this
muscular contraction owes its origin to a force which ema-
nates from the occipital protuberance, a different part of the
brain from that which gives birth to thought. Observations
on paralytics prove that the will is insufficient to produce
movement.

In order that movements may be executed in the order
and with the unity necessary to the accomplishment of the
will, they must be co-ordinate. Several physiologists, and
especially Flourens, have regarded the cerebellum as the
organ essential to this co-ordination of movement. A lesion
of this part of the brain produces a disturbance in locomo-
tion similar to that caused by drunkenness ; but pathological
observation has demonstrated that there is sometimes absence
of co-ordination when the cerebellum is not affected.

The muscles unite in the voluntary movements, some as
motors, and others, antagonistic to these, as the moderators
of movement. M. Duchenne (of Boulogne) has shown that
in the voluntary movements of the limbs and the trunk these
two systems of muscles, impulsive and modifying, are simul-
taneously contracted by a double nervous excitation; one to
produce the movement and the other to modify it. Without
this unity of intention between the antagonistic muscles, the
movements would lose their precision and their certainty.

Effort. — When one or several groups of muscles contract
themselves strongly in order to perform a function requiring
force, or to overcome an obstacle, to draw or push away a •
body, the name effort has been given to this action of the
muscles. There is effort in walking, climbing, running, and
a great number of other functions. Whatever muscles take

\

60 THE HUMAN BODY.

part in effort they must have a point of support or fulcrum,
directly or indirectly upon the skeleton of the trunk, that is
on the spinal column and the bones of the thorax. An effort
is always preceded by an inspiration which dilates the thorax,
thus rendering the bones of which it is composed immovable
by the contraction of the inspiratory muscles, and furnishing
a fixed point to the muscles attached to these bones. Thus,
one after another, the greater part of the muscles of the
system joins in a movement of which sometimes the arm or
the hand only is the immediate instrument. The proof of
this is the impossibility of making a movement distinct from
that which is the immediate object of the effort, without this
effort ceasing or diminishing. When it is at its highest point,
respiration is suspended, the glottis closes or remains slightly
open, according to the nature and the degree of intensity in
the effort ; the inspired air distends the lungs, and if a part
escapes it is too small to lessen the expansion of the chest;
the abdominal viscera are compressed from above by the
diaphragm in front, and laterally by the muscles of the abdo-
men. During certain efforts the air is expelled slowly through
the glottis, and when the movement terminates suddenly
with redoubled force, the expiration is accomplished rapidly
and sometimes in the form of a cry. The sailor who hauls
in a rope, or the baker as he with difficulty raises the dough
to throw it back into the kneading-trough, accompanies the
movements which he executes with a cry of which the rhythm
expresses the different periods of the effort.

Locomotion. — Man moves over the surface of the ground
by three principal methods of progression — walking, running,
and leaping ; but the point of departure is always the vertical
position. In this attitude, which characterizes the human
race, the equilibrium of the head upon the vertebral column,
and that of the trunk upon the coxo-femoral articulations,
and of the thighs on the legs, is independent of all muscular
contraction, the ligaments being sufficient to insure it. And
farther, the muscles of the neck, of the trunk, and of the
thigh maintain the rigidity of the spinal column, oppose or
prevent the flexion of the knee, and restore the equilibrium
when it is compromised, while the muscles of the leg prevent

THE ERECT POSITION.

61

the flexion, anterior or posterior, of the tibio-tarsal articula-
tion, the surfaces and ligaments of which only permit an un-
stable equilibrium of the body upon the feet. Lastly, the
feet, separated from each other by a distance equal to that

Fig. 20. — The leg in standing.

The foot resting the toes on The foot resting flat on the '

the ground. ground.

which divides the heads of the femurs, complete the mechan-
ism by which man alone, among all living beings, stands
erect with his face placed vertically, and on a plane parallel
to that of the body, but not turned toward heaven, as has
been poetically said.

In the attitude of a soldier without arms, with the heels
touching each other, and the feet forming nearly a right
angle, a stronger contraction of the muscles of the leg is

62 THE HUMAN BODY.

necessary, and consequently fatigue is sooner induced. When
resting on one foot only the body departs laterally from the
vertical and leans a little backward, the leg which supports
only its own weight rests on the ground, with the muscles
completely relaxed, acting as a support and counterpoise.
This attitude when standing is the least fatiguing, firmest,
and also the most elegant; it is the one preferred by painters
and sculptors, and was considered by Leonardo de Vinci as
the most natural.

When the body moves it is divided into two quite distinct
sections: the one, comprising the head, trunk, and upper
limbs, representing the mass to be transported; the lower
limbs are at once the movable supports of the superior parts
of the body, and the agents of propulsion which communi-
cate to them the movement of translation. In all move-
ments of this nature the trunk inclines forward at an angle
which varies according to the quickness, from 5° 7' in the
slowest walk to 22° 5' in the fastest running. From this
position there is a constant tendency to fall forward, which
is neutralized by the moving of the lower limbs in such a
direction as that the heads of the femurs shall always serve
as the point of support for the body. M. Longet compares
this unstable equilibrium of the body upon the femurs to
that of a rod on the end of a finger, so inclined that the
only means to prevent its fall is to carry the finger forward
in the same direction as the inclination, more rapidly as this
inclination becomes greater.

By their alternate flexion and extension the lower ex-
tremities give an impulsion to the trunk, they lengthen and
contract in a direction inclined to the horizon, since it is
forward and not vertically that they push the body; the re-
sult is that the centre of gravity sinks toward the ground just
in proportion to the rapidity of the mode of progression.

Each extremity props itself by turns on the ground, and
then the impulse being given the knee bends, the heel rises,
the foot is lifted, the limb, shortened by flexion and sus-
pended from the pelvis, is directed from behind forward,
and is again placed upon the ground.

In this movement the leg, according to the brothers

WALKING. 63

Weber, represents a pendulum which bends and oscillates
by its weight alone; according to M. Duchenne (of Bou-
logne), it obeys the contraction of the flexor-muscles.

The experiments of the Webers having demonstrated,
as stated above, that the head of the femur is retained
in the cotyloid cavity by atmospheric pressure alone, these
skilful observers conclude that in the second movement in
walking the weight of the thigh alone determines the flexion
of the joints and the oscillation of the three segments of the
pendulum, which is then represented by the lower extremity.
Basing his opinion on pathological observation, M. Duchenne
thinks that the contraction of the flexors of the thigh, leg,
and foot is the real cause of the second movement of the
extremity in walking, and that the action of weight contri-
butes very little to it. According to M. Beclard, the tonicity
of the flexor-muscles, developed by extension, suffices for
seconding the pendulum movement of the lower limb.

In walking the body advances without ceasing to rest
upon the ground, and by effecting a succession of move-
ments, which are divided in each step into two principal
ones. First, — the body rests upon the two lower limbs ; the
right leg, placed behind and inclined to the horizon, touches
the ground at the extremity of the metatarsus and at the
toes, it stretches out, and the foot is raised to an angle of
forty-five degrees; now the left limb is placed forward, rest-
ing on the ground on its sole, the knee is a little bent, the
heel exactly under the head of the femur, and the trunk
slightly inclined forward. Secondly, — the left leg alone sup-
ports the weight of the body; it lengthens by extending the
knee and straightening the foot; its direction inclines to the
horizon, and the body pushes itself forward, while the right
leg is raised from the ground by bending the knee, follows
the movement of translation given to the body, executes
half an oscillation, and touches the ground, first at the heel,
which places itself exactly under the head of the femur, and
then on the sole of the foot on which the body rests.

To accelerate his movement man inclines more forward,
the centre of gravity falls nearer to the earth, and the flexion
of the limb placed behind is greater, the pendulum is shorter

64 THE HUMAN BODY.

and its oscillation more rapid; at the same time the greater
flexion gives more force to the extension, and the impulsion
forward is increased; and more still, extension acts in a direc-
tion still more inclined, which results in a lengthening of
the step. The motion is also increased by the extension of
the leg resting on the ground while the other oscillates, in
such a way that when the latter touches the ground the
former detaches itself in order to swing in its turn. In
walking quickly the body rests upon the ground only by one
foot at a time.

When walking, and especially when walking rapidly, the
arms accompany with their isochronous oscillations the
movements of the lower limbs, and contribute to maintain the
equilibrium: indeed it is next to impossible to walk quickly
when the arms, from any cause whatever, cannot oscillate.

According to the experiments of the brothers Weber, the
speed of a man of ordinary stature is, in rapid walking, about
10,267 yards per hour. This speed could not long be main-
tained, and must be considered as exceptional. In ordinary
walking the speed is nearly four miles an hour, and can
be kept up for a long period But exercise and a special
aptitude for it enable some men to walk great distances in a
relatively short space of time. Trained walkers have gone
seventy-five miles in twenty hours, and walked the distance of
thirty-seven miles at the rate of five miles an hour. The moun-
taineers of the Alps are generally good walkers, and some
of them are not less remarkable for endurance than for
speed. Jacques Balmat, who was the first to reach the sum-
mit of Mont Blanc, at sixteen years of age could walk from
the hamlet of the Pe'lerins to the mountain of La Cote in
two hours — a distance which the best trained travellers re-
quired from five to six hours to get over. At the time of
his last attempt to reach the top of Mont Blanc, this same
guide, then twenty years old, passed six days and four nights
without sleeping or reposing a single moment. One of his
sons, Edward Balmat, left Paris to join his regiment at
Genoa; he reached Chamonix the fifth day at evening,
having walked 340 miles. After resting two days he
set off again for Genoa, where he arrived in two days.

WALKING — TROTTING. 65

Several years afterward this same man left the baths at
Loueche at two o'clock in the morning, and reached Cha-
monix- at nine in the evening, having walked a distance
equal to about seventy-five miles in nineteen hours. In 1844
an old guide of De Saussure, eighty years old, left the hamlet
of Prats in the valley of Chamonix in the afternoon, and
reached the Grands Mulets at ten in the evening, then after
resting some hours he climbed the glacier to the vicinity of
the Grand Plateau, which has an altitude of about 13,000
feet, and then returned without stopping to his village.

We will cite in addition the performance of a man from
Thun, who walked in September, 1867, a distance estimated
at forty Swiss leagues in twenty-three hours, representing at
least thirty-four hours of walking for ordinary travellers.

Running differs from walking principally in the fact that
at a given moment the body leaves the ground, and passes
through space in the same manner as a projectile. The
body is inclined more forward, and the centre of gravity is
lower than when walking. The lower limbs execute the
same alternate movements as in the first mode of progres-
sion; but at the moment when the right leg leaves the
ground and commences its demi-oscillation, the left, which
is bent and only touches the ground at the extremity of the
foot, pushes rapidly forward, and with sufficient force to
throw the body upward and forward, and the two legs oscil-
late together during an instant, then the one which left the
ground first falls before the other on the point of the toes.
The body has made a spring, and the same manoeuvre takes
place alternately on each side, and the result is a succession
of springs which constitute running.

Trotting is running when the impulsion forward is not so
strong, and the movements are less rapid, which renders it
more applicable to uneven ground, where it is necessary to
choose the place where the foot is to be placed at each step.

The greatest attainable speed for a man is, according to
the brothers Weber, seventeen miles in an hour; but if this
speed has ever been maintained for one hour, which is
doubtful, it could not certainly be continued much longer.
The maximum of speed attained in the gymnasium of

66 THE HUMAN BODY.

Amoros was twenty-five miles in two hours and forty-five
minutes, that is, about nine miles an hour.

Leaping is, properly speaking, nothing but a step of run-
ning taken singly. A man can jump with his feet joined,
that is to say, the two feet quit the ground at the same in-
stant, and the body is thrown vertically upward and forward,
or backward. The jump may be preceded by running seve-
ral steps in order to get under way, as it is termed. In this
case the speed acquired during the first steps is added to the
impulse given to the body by the last one. By exercise
men have succeeded in jumping vertically a height of two
metres, and horizontally over a space of five or six metres.
Amoros speaks of an Englishman who jumped across a ditch
ten metres in width.

Swimming. — Man can sustain himself upon the water, and
traverse it for a considerable space by swimming; but this is
not an instinctive method of locomotion for him — he must
learn to swim, while walking and the other modes of pro-
gression are natural to him, and are not acquired by study.
Man walks, runs, and jumps just as an amphibious animal
swims without having learned to do so; but to swim he must
study the attitudes and the movements which neutralize the
effect of his specific gravity, which prevent him from sinking
into the water, and permit him to gain a resting-point in
order to displace it.

The quadruped swims as if walking in the water, that is,
by making just the same movements as in walking on the
ground. Man can, it is true, swim as animals walk, striking
the water with his four members ; but he is soon overcome
by fatigue, and to swim for any length of time he must exe-
cute other movements considerably complicated in their
combinations. It is from that modest amphibian, the frog,
from which he borrows in this case the method of progres-
sion, and this loan is certainly the most inoffensive of all
those which he makes from the animals. Although he seems
to turn his members quite away from their normal functions,
he soon attains the power of prolonging this exercise, which
is eminently healthful and very precious, since he finds in it a
means of saving his own life and the lives of his fellowmen.

CHAPTER VI.

The head. — The skull, bones of the skull, sutures, arch of the skull, base of
the skull. — Measurement of the skull; facial angle, angle of Daubenton;
comparison of the superficies of the skull and of the face. — System of
Gall. — The face, boms of the face, upper jaw, loiver jaw.

The Head. — The head is the most important part of the
body, and to it and to the organs which it contains our
attention is most particularly attracted. The heart and
lungs support life by the respiration and the circulation,
the digestive apparatus nourishes the body, but the head is
the seat of intelligence, the centre in which all the nervous
impressions meet and from which radiates the will. In the
head are united the organs of sight, of hearing, of smell, and
of taste ; the face, almost entirely formed by the grouping of
these organs, expresses by the aid of numerous muscles the
impressions transmitted to the brain, the passions, calmness
or agitation of mind, and, within certain limits, the phases
of thought. In other regions of the body life is unconscious,
and the functions in their performance, whether healthy or
diseased, are executed mechanically; the head alone perceives
sensations and interprets their meaning, it is by it that man
knows himself, by it he feels that he lives, and is able to
say, "I think, therefore I am."

The head is formed of two distinct parts : first, the skull,
a bony case which envelops the brain, and incloses in the
thickness of one of the bones of which it is formed the organ
of hearing; secondly, the face, in which are united the
organs of sight, of smell, and of taste.

The skull is composed of eight bones: the frontal or
coronal, which corresponds to the forehead or sinciput; the

68 THE HUMAN BODY.

occipital in the posterior part of the skull or occiput; the two
parietal bones, which form the side walls of the skull, and
contribute, with the frontal and occipital, to form its arch;
the two temporal bones occupy, as their name shows, the
region of the temples; the ethmoid, which owes its name to
the sieve-like plate of its upper surface ; and the sphenoid, so
called because it is wedged in between all the other bones
with which it articulates, and which rest upon it as upon the
keystone of an inverted arch, thus forming the base of the
skull on which the brain rests. The frontal, occipital, pari-
etal, and temporal bones are flat, formed of two plates of
ivory tissue — internal and external tables — between which is
a more or less thick layer of spongy tissue.

The bones of the cranium are united by means of sutures
formed by the junction of the teeth of their serrated borders,
almost precisely like what is termed in architecture dove-
tailing. At birth the bones which form the arch of the skull
are united only by a membranous tissue, and their borders
overlap each other even on slight pressure in such a way as
to lessen the diameter of the head ; but although the sutures
are not yet developed, a part of the tooth-like processes
already exists in a rudimentary state. The membranous
intervals are greater at the point of union of the occipital
and frontal with the parietal bones; these spaces are called
the fontanelles. They are soon filled with bony tissue, and
at four years of age not a trace of them remains. About
the end of the third year the borders of the bones are cut
into fine notches or teeth, which increase in number till the
period of adolescence. Before this the suture which unites
the two halves of the frontal bone begins to disappear; and
later still, when the brain is fully developed, the other
bones gradually close together.

The internal surface of the skull presents a series of
depressions, portions of the arch which have been called
fossa, and according to the bones which constitute them, the
frontal, occipital, and temporal fossce, and which correspond
to the projections which we see on the external surface.
There are also a great number of projections and depressions,
which to a certain extent are modelled to the surface of the

THE SKULL — THE FACIAL ANGLE. 69

brain, but which form no relief on the outside of the skull.
There is no opening in the arch of the skull, but there are
several in its base through which the nerves and blood-
vessels pass; the most important of these is the foramen
magnum, which is the communication between the cavity of
the skull and the vertebral canal.

The skull is oval in form flattened at the base, with the
larger end at the back. It is never perfectly symmetri-
cal, and differs in shape and size according to age, the in-
dividual, and the race. It is larger in proportion in the
infant than in the man, and in the white race than in the
other races. But whatever may be the varieties which it
presents, they appear exclusively in the arch.

Starting from the principle that the skull is modelled upon
the brain, in measuring its dimensions we seek to ascertain that
of the organ which it incloses. To attain this object, Camper
drew two straight lines, the one starting from the first in-
cisors of the upper jaw and passing over the median line of
the forehead ; the other starting from the auditory canal and
carried horizontally till it encountered the first, formed with
it an angle called the facial angle, which is from 80 to 85
degrees in the European, 75 in the Mongolian race, and 70
in the Negro. This anatomical character, considered as an
expression of intelligence, did not escape the notice of the
artists of antiquity. The statues which they have bequeathed
to us prove this ; among their gods, the facial angle of Jupiter
Trophonius, for example, is 90 degrees.

Daubenton proposed to measure the occipital angle to com-
plete the measurement of Camper, which applied only to the
anterior portion of the skull; but these angular measure-
ments would not give the extent of a solid nor of a cavity;
the thickness of the bones at certain points, and the varying
development of the cavities or sinuses comprised between
the internal and external tables, would take from these
measurements much of their signification. In order to be
more exact, Cuvier, dividing the head by a section from
front to back, compared the area of the skull with that of the
face, leaving out the lower jaw: he found that in Europeans,
the area of the skull was four times that of the face, and in

70 THE HUMAN BODY.

the Negro the area of the face is greater by a fifth, that of
the skull being proportionally less.

This last method of measurement, even though it gives an
idea of the relative intelligence within narrow limits only,
is at least founded upon certain facts, and it expresses the
law of the proportional development of the face and skull in
the superior animals. And even in measuring by the facial
angle the causes of error may be avoided to a certain extent,
and this measurement is an expression of an incontestable
anatomical fact.

But this is not the case with a doctrine which was received
with enthusiasm about the beginning of this century, though
now almost forgotten. We speak of phrenology. Gall pro-
fessed to discover the degree of development of the faculties
by exploring the cranium. According to his theory, the
skull is moulded upon the brain, and presents protuberances
corresponding to those of that organ, and thus gives the
measure of the development of the intellectual and emotional
faculties. These faculties, which he localized in the ence-
phalon, were composed, according to him, of a series of
conoid bundles, the base of which corresponded to the sur-
face of the brain and the apex to the medulla oblongata.
Each one of these cones was the seat of a faculty, of which he
numbered twenty-seven, placing all the intellectual faculties
in the anterior portion of the brain, the animal faculties in
the posterior portion, and the moral faculties in the middle
portion over the ear : the first confined for the most part to a
very small space, and the others distributed over larger
surfaces. The pupils of Gall added eleven faculties to those
which he had classed. Among the latter, the sense of
right and wrong — or as they termed it, conscientiousness —
did not appear.

To this system it was objected that if the principal projec-
tions of the exterior of the skull, the frontal and parietal
protuberances, for example, correspond to the depressions
or fossae of the interior, no external relief indicated the
digital impressions and the small cavities which correspond
to the surface of the brain ; that at several points an external
projection corresponded to one on the inner surface; that

THE SYSTEM OF GALL — THE FACE. 71

the arch of the brow (the superciliary ridge), where six
faculties are located, is more or less prominent, not from
the cerebral relief, but from the development of the frontal
sinuses; a,nd that there is no resemblance between the form
of the internal table and the external table in the frontal
region. Gall was therefore wrong in tracing upon the brain
the seat of each faculty according to the elevations which
he found upon the skull. It was added also, that, even
admitting the localization of the faculties and the divisions
of the brain, it was very irrational to unite all the faculties
in corresponding portions of the cranial arch, and to attri-
bute none at all to those portions of the brain which are not
in contact with the skull, or which rest laterally and in front
on its base. This exclusive grouping was unjustifiable, and
is to be considered as purely arbitrary.

Gall and his school invoked the aid of the comparative
anatomy of the brain in support of his system. Leuret gave
them a death-blow by showing that the study of the brain
in the animal scale proves the facts to be in entire disagree-
ment with the theory of the German savant, and that it dis-
proves at all points the propositions of phrenology.

The face is composed of fourteen bones, which form, by
their union with each other and with the bones of the skull,
the cavities in which the organs of sight, of smell, and of
taste are placed. Twelve of these bones are in pairs, and
placed symmetrically on each side: these are the superior
maxillary, the malar or cheek bones, the nasal bones, the
lachrymal bones, the superior turbinated bones, and the
palatine bones. Two are not paired: these are the vomer
and the inferior maxillary. The superior maxillaries, with
the lachrymal and malar bones, combine to form the inferior
portion of the orbit; they are united to the temporal bones
by the malar bones, the protuberances of which form the
cheek-bones. At their alveolar border the teeth are placed,
and the space included in the dental arch is called the pala-
tine arch, which is prolonged backward by the palatine bones.
The nasal bones form the upper portion or root of the nose ;
below these, and between the superior maxillaries, is the
nasal cavity, which is divided into two parts by a partition,

72 tHE HUMAN BODY.

of which the vomer forms a portion. The superior turbinated
bones articulate with the maxillaries and contribute to mul-
tiply the nasal sinuses, in which are the ramifications of the
olfactory nerves.

The inferior maxillary is at first composed of two bones,
which are early joined together at the point called the sym-
physis of the chin. The branches of this bone form a right
angle with its body, called the angle of the jaw> and at their
superior extremity they divide into two apophyses; namely,
the condyle, which articulates with the glenoid cavity of the
temporal bone, and the coronoid process, where the tendon
of the temporal muscle is inserted. This is one of the
muscles which draw the lower jaw to the upper one in chew-
ing the food.

This skeleton, with its strange and imperfect outlines, this
type of Death, disappears under the muscles and teguments,
which cover it with an elegant envelope. The eyelids veil
the orbit and protect the eye, the watchful sentinel and inves-
tigator of the exernal world, the admirable instrument which
enables the brain to contemplate the works of creation and
to express its most vivid impressions. The nose covers the
organs of smell, while it completes them by protecting their
sensibility; the lips are placed before the mouth, and they
are at once an organ of prehension, a docile and indefatig-
able guard, a necessary instrument in articulating sounds,
and one of the most expressive of the features which com-
bine to form the physiognomy. The concha, or external
ear, surrounds the auditory canal, and serves to collect the
sonorous waves, and to give expression to the head. The
hair, the eyebrows, and eyelashes protect the skull and the
eye against external objects, and at the same time their dif-
ferent shades, and curves, and undulations, greatly contri-
bute to the beauty of the whole. Lastly, the skin of the
face is animated with the most delicate tints, or is clothed
in the vigorous tones and that admirable carnation which
has been so well rendered by the Venetian painters.

CHAPTER VII.

Digestion. — Waste of the organism repaired by alimentation. — Hunger. —
Thirst. — Organs of digestion ; abdominal cavity, peritoneum. — Diges-
tive apparatus. — Mouth, lips, cheeks, teeth, palate, soft palate, tongue. —
Pharynx. — (Esophagus. — Stomach. — Intestinal canal; small intestine,
large intestine, intestinal convolutions, mesentery, omen turn. — Mucous
membrane. — Liver. — Pancreas. — Spleen . — Kidneys. — Mechanism of
digestion. — Digestion of the stomach, gastric juice, peristaltic movement,
chyme. — Intestinal digestion, bile, pancreatic juice, chyle. — Absorption;
endosmosis, exosmosis, functions of the veins and lymphatic vessels in
absorption, rapidity of absorption.

Digestion. — The human body loses every day through vari-
ous channels, by exhalation or excretion, about 310 grains
of nitrogen, an essential principle of animal matter, and
6^2 Ibs. of water, and burns io*/2 ounces of carbon in
contact with the oxygen of the atmosphere. A very short
time, therefore, is sufficient to exhaust the organism if it does
not find in the alimentation the new elements by which it
is reconstructed. Of this unceasing necessity of repairing
the loss which the organs sustain by the action of life, man
is imperiously reminded by hunger and thirst; hard condi-
tions of existence. He can support the first of these wants for
a time, which varies according to age and individual strength;
it is a sensation agreeable at first, but it soon becomes a
torture, a succession of atrocious pains, and moral and physi-
cal destruction follow. The annals of hunger are terrible in
science and in history; it has been called, with too much
reason, an evil counsellor, and he who has the means to
appease it each day should be thereby reminded of those
less fortunate than himself.

74

THE HUMAN BODY.

Thirst is a sensation painful from the first, and can be
borne for a shorter time than hunger ; for it necessarily im-
plies the privation of all liquid aliment, and exhaustion super-
venes much sooner than when a
man is deprived of solid food,
but is able by the aid of a little
water to prolong his life for some
days.

The organs of digestion, of which
we will give a summary idea, are,
for the most part, contained in
the abdomen.

Abdominal cavity. — This ca-
vity is the largest in the body; it
is situated below the chest, from
which it is separated by the dia-
phragm, and extends to the lower
' extremity of the trunk. It is
divided into several parts or re-
gions, which are — ist. In the
upper portion, the epigastrium,
corresponding to what is called
the pit of the stomach, and the
two hypochonders (hypo, under;
chondros, cartilage), which rise up
from each side of the epigastrium,
under the double arch of the

Fig. si.— Section of the trunk and its diaphragm and under the car-
tilages of the ribs. 2d. In the
middle, the umbilical region, and
the flanks or sides. 3d. In the
lower portion, the hypogastrrum
or lower belly, and the iliac
fossa, inclosed by the bones of the same name. The walls
of the abdomen are formed principally by muscles and apon-
euroses, combined with the vertebral column and the bones
of the pelvis. The lower or false ribs have only an in-
direct connection with the abdominal cavity, resulting from
its being set into the. bottom of the chest

cavities in the median line.

A. Cavity of the chest.

B. Diaphragm.

C. Abdominal cavity.

D. Vertebral column.

E. Spinal canal.

ABDOMINAL CAVITY — ORGANS OF DIGESTION. 75

The abdominal cavity is lined with a serous membrane
called the peritoneum. Like all the membranes of this
nature, it is formed of cellular or laminated tissue and
elastic fibres; its free surface is covered with an epithelium,
a sort of epidermis, which resists the continual friction result-
ing from the movements of the organs; and lastly, like all
its congeners, it is a sac without an opening, folded on itself,
and consequently with double walls. The space between
these walls is empty, their corresponding surfaces rub freely
against each other, and are moistened by a fluid analogous
to the serum of the blood, a secretion peculiar to these
membranes, and from which they derive their name. The
internal wall of the sac covers all the organs which it con-
tains, and the external wall is attached throughout its whole
extent to the cavity which it lines. We shall, by-and-by,
have occasion to return to the disposition of the peritoneum.

The digestive apparatus is one of the most complex and
extensive in the organism; it is accessible to our investiga-
tions in all its parts, and we are able to follow the working
of the functions which devolve upon it. We can observe
the metamorphosis which the food undergoes; we can repro-
duce in our laboratories a part of these transformations; a
step farther, and, as Fontenelle has said, we should surprise
nature in the very act; but this impossible step is the immense
distance which separates inert matter from organized sub-
stance, physical and chemical phenomena from the vital
functions.

The organs of digestion are the mouth, the pharynx, the
oesophagus, the stomach, the liver, and the pancreas. The
spleen and kidneys are appendages of the digestive apparatus,
but belong rather to the circulatory or excretory.

The mouth forms the entrance to the digestive apparatus;
it contains the organ of taste, and serves in eating and in
articulating sounds. Bounded above by the palatine arch,
below by a muscular wall and by the tongue, on the sides
and in front by the cheeks and the lips, the mouth presents
in front the opening of the lips, behind, the isthmus of the
throat by which it communicates with the pharynx and over
which the soft palate falls.

76

THE HUMAN BODY.

The lips form the anterior wall of the mouth, and are com-
posed principally of the orbicular muscle of the lips, to whose

LLVEILLt DEL.

C. LAPLANTE

Fig. 22. — Section in the median line through the inferior portion of the nasal

fossae, the mouth, pharynx, larynx, oesophagus, and trachea.

A. Mouth. H. Superior vocal chord.

B. Soft palate. I. Inferior vocal chord.

C. Tongue. K. Ventricle of the larynx.

D. Tonsil. L. Larynx.

E. Epiglottis. M. N. Trachea or windpipe.

F. Thyroid cartilage. O. Pharynx, before which is seen the

G. Arytenoid cartilage. cricoid cartilage.

concentric fibres are attached nearly all the muscles of the
face ; a very thick skin intimately united with the orbicular

THE LIPS THE CHEEKS. 77

muscle, a layer of small salivary glands subjacent to it, and the
mucous membrane, complete these two movable, extensible,
and contractile veils. The lips are an organ of prehension
and suction; they prevent, especially the under lip, the
escape of saliva; they assist in the articulation of sounds
and in playing upon wind-instruments; and lastly, they take
an extensive part in the expression of the physiognomy.
Abundantly provided with nerves and vessels, the lips are
extremely sensitive, especially on their borders, where the
skin grows thin, takes a carnation tint, and is insensibly
transformed into mucous membrane. Although the orbicular
muscle limits them in a measure, and imposes upon them
certain functions and a distinct region, they are in reality
only the anterior portion of the cheeks, with which they are
in constant communication by movement and function.

The cheeks form the sides of the face and the lateral walls
of the mouth. They embody in their substance the muscles
intrusted with the performance of the complex functions
of the mouth. One of these muscles, peculiar to that part
of the cheek which forms the buccal wall, brings the food
between the jaws and reacts against the distension of the
cheeks by the air. Its action in playing on wind-instru-
ments has given it the name of buccinator; it contributes
also to the expression by drawing the commissure of the lips
backward, while the great and small zygomatic muscles raise
it. The triangular muscle of the lips, on the contrary, lets
it fall ; and lastly, the masseter, a thick muscle of great power,
brings the lower jaw against the upper one, and with the
temporal muscle performs mastication. The internal face of
the cheeks is covered with mucous membrane, and its whole
surface is scattered over with little openings, which give pas-
sage to the saliva, which is secreted by a great number of
glandules analogous to those in the lips. Near the middle
is the opening of the canal of Stenon, through which the saliva
secreted by the parotid gland is poured into the mouth. This
gland is situated, as its name indicates, in front of the ear,
and is the most important of the salivary glands.

The teeth are implanted in the alveolar border of the upper
and lower jaw, forming two symmetrical arcades, and when the

78 THE HUMAN BODY.

mouth is closed they circumscribe its limits like an internal
wall. They are twenty in number in the child, and thirty-two
in the adult. They are divided into eight incisors, four canine,
and twenty molars. The last four molars are called the
"wisdom teeth." A tooth is composed of three distinct
parts: the pulp, the ivory, and the enamel. Vessels and
nerves penetrate the pulp, but do not go beyond; the ivory
which envelopes the pulp constitutes the root and the crown
of the teeth. That part of the tooth where the crown joins
the root is called the neck. This last is covered with a layer
of bony tissue. The crown commences at the neck, and is
overlaid with the enamel, a tissue very poor in animal sub-
stances, and almost inorganic. The teeth are not bones;
though their roots have an osseous covering, they do not
present either in their essential parts — the ivory and the
enamel — or in their mode of development and their physio-
logical conditions, any connection with the osseous system;
they are considered as analogous to the epidermic productions,
the hair, nails, &c., which they resemble in many respects.

Palate. — The palatine arch is formed, as we have already
seen, by the upper jaw-bones and the palatine bones. It is
circumscribed in front and on the sides by the upper teeth.
It is covered with a thick mucous membrane, very hard, and
presenting transverse ridges. Behind, it is continued by a
musculo-membranous partition, called the veil of the palate —
the soft palate — covered anteriorly by the mucous, buccal,
posteriorly by the pituitary membrane. Its inferior border
is free and floating, presenting on the median line an appen-
dage called the uvula. Each of its lateral borders forms
a continuation with the tongue and the pharynx by two
folds, which are called the pillars of the soft palate, and be-
tween which on either side lie the tonsils. In a state of
repose the soft palate closes the back part of the mouth;
but when raised prevents the food and drink, and the voice
also, from passing into the nasal fossae.

The tongue is a fleshy body, symmetrical, longer than it is
broad, flattened from above downwards, thicker toward the
middle than at its extremities, larger behind than in front,
and rounded on the edges. The posterior extremity of the

THE TONGUE. 79

tongue is called its root, and the anterior the point or tip.
Its upper surface or back, and a part of its edges, are covered
over with papilla, which are divided into conical, fungiform,
and cup-shaped papillae. Its lower surface is free for about
one-third of its length anteriorly : at the point of attachment
we observe a mucous fold called the frcenum lingua or bridle
of the tongue. Its two posterior thirds receive the muscles
which fasten it to the neighbouring parts. The base or root
of the tongue is fixed to the hyoid bone, an osseous semi-
circle bifurcated at its extremities, placed between the tongue
and the larynx, and bound to these two organs by muscles,
which gives unity to their movements in rising and falling.
The tongue is formed of muscles, some of which are proper
to itself, and others attach it to the hyoid bone, to the lower
jaw, and to the styloid process of the temporal bone. All
these muscles interlace their fibres in an inextricable manner,
especially towards the upper portion of the tongue. At the
median line and in the centre they are fixed to a cartila-
ginous plate, a sort of indirect prolongation of the hyoid
bone, which gives greater solidity to the whole. The buccal
mucous membrane covers the tongue, and is remarkably
dense on its dorsal face.

The complex interlacement of the muscular fibres of the
tongue permits a great variety of motion. It can raise or
lower itself, lengthen or shorten, shrink or expand, diminish
the end to a point, bend itself upwards and downwards, hollow
itself into a canal lengthwise or breadthwise, carry its point
and its edges to the parts of the mouth into which mastica-
tion has dispersed the food ; in short, it exhibits in its move-
ments and changes of form great force and the most subtle
dexterity.

The tongue receives three nerves; the great hypoglossal,
the lingual, and glosso-pharyngeal ; the first gives motion, and
the last two are the sensitive nerves of taste. Under the
influence of the first it takes part in the functions of diges-
tion and in the articulation of sounds, and endowed by the
others with a special sensibility, it is the principal organ
of taste.

The bottom of the buccal cavity communicates with the

80 THE HUMAN BODY.

pharynx, a canal with elastic walls formed by muscles, and
lined with mucous membrane. It extends from the back of
the mouth to the oesophagus, and is the vestibule of this
passage, a sort of funnel, the upper part of which shares in
deglutition, and adds to the resonance of the voice. The
anterior wall of the oesophagus is formed by the larynx, the
superior orifice of which, surmounted by the epiglottis, opens
into the pharyngeal cavity, so that it is only the half of a
canal completed in front by the larynx.

The pharynx is continued below by the oesophagus, a tube
formed by two membranes, the external muscular and the
internal mucous. It is extensible and very contractile; it
descends between the spinal column and the trachea, which
it overlaps a little to the left, and on reaching the thorax it
follows the posterior mediastinum, and at last traverses the
diaphragm and opens into the stomach.

The stomach. — The form of the stomach has been com-
pared to that of a bagpipe. It is a large pouch, an expan-
sion of the digestive tube, placed transversely across the
upper portion of the abdomen. Its left extremity or great
cul-de-sac, lying in the hypochondriac region, is rounded and
larger than the right, which corresponds to the epigastrium.
Above, it forms a concave curve — the lesser curvature; be-
low, a convex curve — the greater curvature. The opening by
which it communicates with the oesophagus is to the right
of the great cul-de-sac, and is called the cardiac orifice;
and that which opens into the intestine, the pylorus, or pyloric
orifice.

The walls of the stomach are formed of four membranes,
which, proceeding from without inwards, are a serous — the
peritoneum — a muscular, a fibrous, and a mucous membrane.
The muscular membrane is composed of three layers of
fibres, some longitudinal, others circular. These fibres are
slender and open for the most part, but near the pylorus
they are closer and stronger, and around this orifice they
form a muscular ring, which has been named the pyloric
valve.

The intestinal canal is a continuation of the stomach; its
walls, like those of that organ, are composed of four mem-

THE INTESTINAL CANAL.

8l

branes — a serous, muscular, fibrous, and mucous membrane.
It is divided into the large and small intestines. The
smaller intestine is composed of the duodenum, jejunum,
and ileum. The duodenum is so named because it measures

Fig. 23. — Transverse section of the thoracic and abdominal cavities.

A. Heart

B. Lungs separated to show the heart.

C. Diaphragm.

D. Liver.

E. Gall-bladder.

F. Stomach.

G. Small intestine.
H. Transverse colon.

nearly twelve finger-breadths in length; it extends from the
stomach to the jejunum, from which no line of demarcation
separates it, nor is the jejunum separated from the ileum.
These names indicate a purely arbitrary distinction, drawn
by the ancient anatomists between these three parts of the
intestinal canal. The large intestine differs from the small
one externally in size, and because it presents a series of more

6

82 THE HUMAN BODY.

marked enlargements. The coscum is its upper portion, of a,
larger calibre than the ileum, and separated from it by the
ileo-c&cal valve, a fold of the internal membranes designed to
prevent the reflux of fluids. It opens into the ileum, not at
its extremity, but by a lateral orifice; below this orifice, it
forms a sort of ampulla, terminated by the appendix vermi-
formis. The ccecum is followed by the colon, from which it
is separated only by an artificial division. It is the largest
and longest portion of the large intestine; it forms a curve
called the arch of the colon, and is divided into the ascending,
transverse, and descending colon, to which succeeds the rectum,
the extremity of the intestinal canal.

The total length of the intestine is about nine yards. It
occupies a large portion of the abdomen, in which it is folded
in numerous convolutions.

The peritoneum (peri, around; teinein, to stretch) enve-
lops the intestinal canal, attaches it to the vertebral column
by a double membranous fold, called the mesentery, and par-
tially covers it by a floating fold or epiploon. Imagine a
membrane doubled back so as to form a long broad fold.
At the bottom of and within this fold lies the intestine, which
we may suppose to be stretched in a straight line. The
membrane adheres closely to three-quarters of the surface
of the intestine, and then folds back on itself. The two
leaves of this peritoneal covering are united by cellular
tissue, which permits their separation by distension of the
intestines. If now we pucker the fold at its root, the
border which contains the intestine will form numerous
sinuosities, and this is really the arrangement of the intes-
tinal convolutions. In the region of the colon, the fold
formed by the peritoneum is very much broader, the in-
testine lies in the middle of its breadth, and the rest falls
like a veil in front of the intestinal mass, and rises to the
stomach, which it partially covers as well as the liver and
spleen. This moving veil is the epiploon (epi, upon; pleo, I
float). That part of the fold behind the intestine fastens it-
self to the front of the vertebral column, and takes the name
of mesentery (niesos, middle, and mteron, intestine).

The mucous membrane. — This membrane is to the cavities

MUCOUS MEMBRANE — LIVER. 83

which it lines, what the skin is to the surface of the body.
It is an internal skin, which is a continuation of the external.
Like the skin, it is an organ of absorption and secretion.
It is composed of a corium or true skin and a sort of epi-
dermis, named the epithelium, variable in its texture and in
its elements according as it is to offer more or less resistance.
A peculiar fluid — mucus — is secreted by this membrane and
preserves its softness. The mucous membrane is covered,
throughout the digestive canal, even to the end of the small
intestine, with great numbers of papillae or villi, and espe-
cially on the tongue. In the stomach it has numerous folds,
which are effaced when the organ is distended; and through-
out the smaller intestine it forms the valvitla conniventes,
wrinkles or folds designed to increase the extent of absorbing
surface.

The liver is an organ of a glandular nature, arid, like all
the glands, is designed to secrete a peculiar fluid. It
separates from the blood the elements which constitute bile.
Situated in the right hypochonder, it enters the arch of the
diaphragm ; and it occupies also a portion of the epigastrium,
and then comes in contact with the stomach, the arch of the
colon, &c. ; behind, it corresponds to the vertebral column,
the aorta, and the descending vena cava ; in front to the base
of the chest. It is held in its place by ligamentous folds of
the peritoneum; the most important of these is the suspen-
sory ligament. The form of the liver is difficult to describe :
its upper surface is convex, its lower slightly concave. It is
divided into the right and left lobes; to the latter is attached
an appendage named lobus Spigelii or Spigel's lobe. The
under surface of the liver is marked by the longitudinal and
transverse fissures. Through this last the portal vein enters.
Examined en masse, the liver is of a reddish-brown colour.
Its substance is yellowish, granular, and contained in an
envelope of cellular tissue called Glissorfs capsule. Several
kinds of vessels are found in it: the hepatic artery, which
carries the blood which nourishes the organ; the portal vein,
which carries the blood to the liver which is to be purified;
the hepatic vein, which transmits to the descending vena cava
the blood elaborated by the gland; and lastly, the bile-ducts^

84 THE HUMAN BODY.

which secrete or transport the fluids extracted from the blood
by the liver to the gall-bladder, situated under the right lobe.

The tissue proper of the liver is essentially constituted by
the secretory canals of the bile, each one of which ter-
minates in an acinus or lobule ; a net-work of capillaries of
the portal vein surrounds these lobules, which by their union
in clusters form the liver, and which are so many diminu-
tives of that gland. The secretory ducts are continuous
with the hepatic ducts, and the capillaries of the portal vein
with those of the hepatic veins, which transmit to the inferior
vena cava the blood from which the bile has been separated.
The liver secretes sugar also, which, formed in this gland at
the expense of the blood from the portal vein, is immediately
decomposed, and in health disappears in the process of
nutrition.

Pancreas. — This is an elongated gland situated behind the
stomach : it secretes the pancreatic juice — a fluid analogous
to the saliva, and which the pancreatic canal pours into the
ductus choledochus, near its orifice in the duodenum.

Spleen. — This is a spongy vascular body situated in the
left hypochonder, between the stomach and the false ribs:
it serves as a reservoir in over-fulness of the portal vein. Its
special use and purpose are unknown.

The kidneys are two in number, and are placed on the
right and left of the lumbar vertebrae in the lowest part of
the hypochonders. They are glands of a peculiar and very
complicated structure. They separate the urea from the
blood, and transmit to the bladder the urinary secretion by
two canals called ureters. The upper portion of the kidneys
is covered by the supra-renal capsules, the use of which is
not known.

Mechanism of digestion. — This function consists in the
decomposition, liquefaction, and absorption of alimentary
substances; it prepares the nutriment by separating the
assimilable portions which are to be mingled with the blood
from those which are not fit to enter into the organism.
The aliments undergo in the mouth the first change neces-
sary to their introduction into the digestive canal, which is
also no less important in relation to their chemical trans-

DIGESTION IN THE STOMACH AND INTESTINES. 85

formation. They are here mixed with the saliva, which
penetrates them thoroughly, softens and dissolves them in
part, and thus renders their mastication, taste, and degluti-
tion more easy. The saliva also transforms the amylaceous
substances contained in the food first into dextrine and then
into glycose or sugar; it reduces a portion of the fatty
bodies to an emulsion — that is to say, it separates them into
particles held in suspension in the salivary fluid, and begins
the decomposition which is completed in the digestive canal.

Digestion in the stomach. — From the mouth the alimentary
mass descends through the pharynx and oesophagus to the
stomach, where it mingles with the gastric juice, one of the
most powerful agents of digestion. The gastric juice is
secreted by glandular tubes situated in the mucous mem-
brane of the stomach. It is a colourless fluid, saltish as well
as acid to the taste. It contains, among other elements,
alkaline chlorides, lactic acid, and an organic substance
called pepsine, which is peculiar to it. The gastric juice
pours into the stomach in considerable quantities when food
is introduced into it, mingles there with the mass, softens it,
and induces a fermentation which results in their ultimate
liquefaction. During digestion a characteristic movement
takes place in the stomach and intestinal canal — the circular
fibres of the muscular membrane contract successively from
above downwards, and push the alimentary substances in the
same direction. Gradually as the lower fibres contract the
upper ones relax in order to contract anew. This is called
the peristaltic movement. Under its influence the contents of
the stomach are kept incessantly in motion, mixed with the
gastric juice, and directed toward \htpylorus. This orifice
is so named because it is like a door-keeper to the stomach,
allowing the aliments which have been sufficiently elaborated
to pass out while the others are retained in the organ.
After a time, which varies from three to five hours in dif-
ferent individuals and at different ages, the alimentary mass
is converted into a grayish paste, acid, and almost fluid; it
then takes the name of chyme, and the function of the
stomach, chymification, is accomplished.

Intestinal digestion. — In proportion as the chyme reaches

86 THE HUMAN BODY.

the duodenum through the pyloric orifice, the bile and the
pancreatic juice mingle with it, as the gastric juice does in
the stomach. They both aid in liquefying the chyme by the
water which they contain, and by their special action upon
the substances of which it is composed: the pancreatic juice
continues with even more activity than the saliva to trans-
form the amylaceous matter into glycose. The bile assists
the digestion of the animal matter by reducing the fatty
bodies to an emulsion, and it appears also to act as an
excitant to the function of the intestine; and lastly, a fluid
secreted by the mucous membrane of the intestine, as the
gastric juice is by the stomach, co-operates with the biliary
and pancreatic secretions. Under the influence of these
agents, of the fermentation induced by the pepsine and of
the peristaltic movement, the chyme is liquefied during its
advance through the smaller intestine, and is transformed
into a white milky fluid — the chyle — which the chyliferous
vessels draw from the surface of the mucous membrane, and
carry to the thoracic duct, from whence it goes to be mixed
with the blood.

Absorption. — The moment chyle is formed .digestion proper
may be considered as accomplished, though on this function
also depends the absorption of the chyle, which must still be
perfected in its course through the smaller intestine and the
veins before it mingles with the blood.

The mechanism of absorption is still unknown. It has been
explained as taking place by endosmosis — a phenomenon dis-
covered by Dutrochet, which results from the property which
tissues possess, under certain conditions, of permitting fluid
or gaseous bodies to pass through their capillary canals. If,
for example, two fluids which may be mixed, though they
may be of different natures and different densities, are separ-
ated by a membrane, two currents are established through
this membrane in opposite directions, and of unequal force,
tending to mix the two fluids, the stronger current is gener-
ally produced by the fluid the least dense; and this is called
endosmosis — the feebler current exosmosis. In this experi-
ment the substances mingle without changing their nature;
but it is not so in absorption. The substances absorbed by

ABSORPTION. 87

the organic tissues change incessantly during their progress,
borrowing or lending elements to each one of the molecules
through which they pass. And farther, the different tissues
absorb more or less of the same substance by virtue of pro-
perties which are unknown. In this way a poison which
remains inert on the mucous membrane of the stomach is
rapidly absorbed by the lungs.

The mucous membranes absorb more rapidly than the
skin, and this tissue is more or less permeable according to
its thickness, its density, as the epidermis which covers it is
thick or thin. Absorption is therefore very rapid in inocula-
tion— that is, when the substance to be absorbed is intro-
duced into the substance of the tissues. Wherever the point
of absorption may be, it takes place by the lymphatic vessels,
and especially by the veins. The veins absorb a greater
number of substances than the lymphatics, and carry them
more quickly into the circulation; they charge themselves
especially with the materials which are to be rejected from
the economy, while the lymphatics absorb from preference
those that can still be assimilated. The veins and the
chyliferous vessels, which are a variety of the lymphatics,
draw from the mucous membrane of the intestine the useful
products of digestion ; but the lymphatics take possession of
fats, while the veins prefer fluids, albumen, sugar, and salts.

It is well known with what rapidity certain substances
taken into the alimentary canal, or into the lungs, pass into
the other organs, and exhale, or are eliminated. Thus the
presence of the ferro-cyanide of potassium has been recog-
nized in the urine within one minute after its ingestion into
the stomach. Indigo, gallic acid, and other colouring
matters, or those possessing a characteristic odour, pass in
the course of fifteen or twenty minutes through all the wind-
ings of the circulation.

As has already been stated, absorption takes place much
more rapidly by the skin when it has been deprived of its
epidermis. Five or six minutes are generally a sufficient time
for the alkaloids of opium or belladonna to manifest their
action on the nervous system, and in some cases this action
is produced in a few seconds. Other substances, especially

88 THE HUMAN BODY.

sulphate of copper, are almost as rapid in their effect on the
stomach as chloroform and several gases when placed in
contact with the mucous membrane of the lungs; they pro-
duce phenomena which develop themselves with terrible
rapidity. Medicine derives great assistance from this ab-
sorbent property of the tissues; thanks to which, humanity
is daily spared a vast amount of suffering.

CHAPTER VIII.

Respiration. — Thoracic cavity; pleura. — Organs of respiration: lungs,
trachea, bronchia. — Respiration; influence of respiration on the blood,
Lavoisier^- theory, theory of catalytic phenomena; mechanism of respira-
tion, respiratory sounds, frequency of respiration; capacity of the lungs;
modification of t/ie air in the lungs. — Influence of atmospheric pressure
on respiration; mountain-sickness.

Thoracic cavity . — The thorax or chest, as we have already
seen, is formed by the vertebral column, the ribs, and the
sternum. The shoulder-blades and collar-bones belong to
the arm, which is an appendix of the thorax. The thorax
resembles a bony cage (fig. 1 1, p. 27), the interstices of which
are filled with the muscles; the interior of this cage is the
thoracic cavity (fig. 21, p. 74). It is the second cavity in
point of size in the body; it has the form of a cone, slightly
flattened from before backwards, with the base turned down-
ward, and hollowed out in front. It is bounded at its apex
by the sternum, the clavicles, the first rib on the right and
left, and the seventh cervical vertebra; at its circumference
by the sternum, the ribs, and the dorsal vertebrae; at its base
by the false ribs, the costal cartilages, and the xyphoid car-
tilage. The diaphragm corresponds to this base (fig. 21,
p. 74); this is a muscular partition, the fibres of which radiate
from a central aponeurosis ; it closes the chest at the bottom,
into which it rises like an arch, a little depressed in the
centre. The diaphragm is attached to the cartilaginous
border of the false ribs, to the xyphoid process, and to the
lumbar vertebrae. This last attachment is effected by mus-
cular fasciculi, which are called the pillars of the diaphragm.
The central aponeurosis of this muscle is in the form of a

90 THE HUMAN BODY.

clover leaf; it was considered a nervous centre by the
ancients, perhaps because of the pain and the peculiar sen-
sations induced in the epigastrium by strong emotions, or
because they confounded the tendinous fibres with the
nervous tissue.

Pleura. — The cavity of the chest is lined with a serous
membrane, called the pleura, which forms in each half of
this cavity a sac without an opening. There are therefore
two pleurae, a right and a left. Proceeding from the edges
of the sternum and the costal cartilages, the pleurae cover the
lateral walls of the chest and a portion of the body of the
vertebrae. They then approach each other, leaving a space
between them called fas posterior mediastinum. On reaching
the root of the lungs, they turn from within outward, covering
a portion of the pericardium and of the internal surface of the
lungs, their posterior borders and external surface ; they then
penetrate the interlobular fissures, and fold back upon the
anterior border of the lungs and upon their internal surface
quite to their roots; then turning again forward, they cover
the sides of the pericardium, in front of which they turn back
to back, and then separating anew, they reach the borders
of the sternum from whence they sprang. The space left
between the pleurae behind the sternum is the anterior medi-
astinum, separated, as is seen, from the posterior mediastinum
by the heart and the root of the lungs. At the top of the chest
the pleurae form a conical cavity, which receives the apex of
the lung; at the bottom they cover the superior surface of the
diaphragm. In the posterior mediastinum are the oesophagus,
the aorta, the azygos vein, the thoracic duct, and the lower
portion of the trachea. In the anterior mediastinum are the
pericardium — the envelope of the heart — and the thymus
gland, an organ whose uses are unknown. That part of the
pleurae which envelops the organs of the chest, and that
which lines the walls of this cavity, are thus in contact with
each other without adhering, in a normal condition, and they
allow the expansion and contraction of the lungs and the
walls of the chest. The serous nature of the pleurae insures
freedom of movement, and prevents all roughness in the
constant friction of the surfaces.

LUNGS.

91

Organs of respiration. Lungs. — As their name indicates
(pneumon, from pneo, I breathe), the lungs are the essential
organs of respiration. They are two in number, though they

Fig. 24. — Lungs and heart.

A. Lungs ivith the anterior edges

turned back to show the heart
and bronchia.

B. Heart.

C. Aorta.

D. Pulmonary artery.

E. Ascending vena cava.

F. Trachea.

G, G. Bronchia.

H, H. Carotid arteries.

I, I. Jugular veins.

J, J. Subclavian arteries.

K, K. Subclavian veins.

P, P. Costal cartilages.

Q . An tcrior ca rdiac a rtery.

R. RigJit auricle.

receive the air by one canal and the blood by a single vessel ;
they maybe considered as the terminal expansion of the rami-
fications of the trachea, or as the two heads of a single tree.
Placed in the chest, of which they occupy the larger part,

92 . THE HUMAN BODY.

and to the shape of which they are moulded (fig. 23, p. 81),
they represent two irregular cones, resting their bases on the
diaphragm, filling with their apices the two conical spaces
lined by the pleura at the top of the chest, and separated by
the heart and the mediastinum. The right lung is divided
in its length into three lobes by two oblique clefts, and is
shorter and larger than the left, which has but two lobes.
The internal face of the lungs is concave; about the middle
the bronchia unite with the pulmonary vessels to form the
root of the lungs ; their base takes the form of the convexity
of the diaphragm; their edges, thin in front and at the bottom,
thick and rounded behind, partially cover the heart, and fill
the space which separates the diaphragm from the walls of
the thorax, as well as the groove between the ribs and the
vertebrae. The entire surface of the lungs is smooth and
moistened with serous secretion.

The tissue proper of the lungs, or pulmonary parenchyma,
is of a grayish rose colour, soft, spongy, elastic, crepitating
under pressure in consequence of the air it contains. It is
divided into polyhedral lobules, very variable in form and in
the disposition of their facets, which permit exact juxtaposi-
tion without intervals; and they are separated by partitions of
cellular tissue, independent and without communication with
each other. Each one of these lobules is formed of a cluster
of little cavities called pulmonary vesicles, constituting a cul-
de-sac, and receiving the air from the bronchial ramifications
of which they are the terminal expansions. The diameter of
these pulmonary vesicles is from one-seventieth to one hun-
dred and fiftieth of an inch; from this we can judge of the
tenuity of their walls, in the substance of which notwithstand-
ing ramify the capillary vessels. Each lobule represents a little
lung, a diminutive of the entire organ. A bronchial twig and
minute artery run into it, veins and lymphatic vessels leave it.
On the surface the lobules appear bounded by their interme-
diate partitions, and they form a mosaic of which the mottled
colouring varies from rose to black. These black particles
are principally composed of a carboniferous substance which
penetrates the lung either with the air or with the blood, and
which is called pulmonary carbon.

LARYNX TRACHEA.

93

The lungs are supplied with air through the larynx, trachea,
and bronchia. The larynx, the organ of the voice, of which
we shall speak later, is continuous below with the trachea.
This is a cylindrical tube flattened behind; it is composed
of a series of cartilaginous rings united by a fibrous membrane,

Fig. 25. — Section showing the ramifications of the bronchi in the lungs.
A. Trachea. B, C. Bronchi. D, D. Bronchial tubes.

and lined with a mucous membrane; it is placed in the an-
terior portion of the neck, and passes vertically from above
downward. The rings of the trachea do not extend quite
round it; interrupted in their circuit towards the posterior
fourth of the tube, they are, properly speaking, only segments
of a circle. They number from sixteen to twenty, and pro-
duce a corresponding number of protuberances on the surface
of the trachea, which is thereby rendered rough and wavy to
the touch. It is from this circumstance that it derives its

94 THE HUMAN BODY.

name (trachys, rough). Formerly it was confounded with
the arterial vessels, which were supposed also to be designed
to contain air.

At the height of the third dorsal vertebra, the trachea
divides into two portions, which are called bronchi, which
on reaching the root of the lungs divide into numerous rami-
fications designated bronchia or bronchial tubes, and be-
coming more and more slender. Of the two principal
bronchi, the right is larger than the left, and the left is twice
the length of the right. They are both, as well as their rami-
fications, up to a certain limit, composed of fibrous membrane
and incomplete cartilaginous rings. When their diameter has
decreased to less than one-fiftieth of an inch, they no longer
have the cartilaginous rings, and the mucous membrane
cannot be separated from their walls. They continue to
subdivide, and terminate, as already stated, in the pulmonary
vesicles, the agglomeration of which in clusters forms the
lobules of the lung.

Independently of the artery and pulmonary veins by which
the venous blood reaches the lung, and, transformed into
arterial blood, is returned to the heart — that is, besides those
which serve for the sanguification and circulation — the
bronchial veins and arteries carry the blood through the
lungs which is destined to nourish the organ itself, and it is
probable that the tissue proper of the lung uses for itself part
of the red blood formed in its cavities. Numerous lymphatic
vessels are also found in the lungs. The nerves which are
distributed through the lungs come from the pneumogastric
and the ganglion ic nervous system.

Respiration. — Respiration is a function by which the
oxygen of the air is introduced into the blood, and by which
part of the useless and hurtful materials are expelled, in a
gaseous form, from the organism. It is divided into two
parts : inspiration, during which the atmospheric air penetrates
the pulmonary cells; and expiration, which expels the air
which has been changed during its stay in the lungs. On
reaching the cells of the lungs, the blood is separated from
the air by their walls and those of the capillaries, which
ramify over them. However thin these membranes may be,

RESPIRATION. 95

they suffice to confine the air and the blood in distinct
cavities; but like the other organic tissues, they have the
property of allowing themselves to be penetrated by endos-
mosis and exosmosis. The oxygen of the air therefore passes
through them in order to combine with the blood; while those
gases contained in this fluid, which should be eliminated,
separate from it and mingle with the air, which carries them
away with it during expiration. It is an interchange of gases
between the air and the blood, the air giving up oxygen
to the blood, and receiving from it other gaseous fluids,
among which carbonic acid gas predominates in volume.
This being in excess in the venous blood is exhaled from
the lungs, while the oxygen of the air combines with the
blood which is carried to the heart by the veins, which has
been deprived of a part of its nutritive elements, and has
become unfit to support life. On coming in contact with
the oxygen, the venous blood loses its dark colour, becomes
a brilliant red, and returns to the heart transformed into arte-
rial blood. This group of phenomena is called sanguifi-
cation.

On the one hand the oxygen of the atmosphere burns
carbon in the lung, on the other the lung exhales carbonic acid
gas, nitrogen, and the vapour of water. From whence are
these gases and this water derived? The carbonic acid gas
is not produced in the lungs alone. The venous blood
reaches the organ of respiration poor in oxygen, and charged
relatively with the carbonic acid gas which it has received in
its course from all the tissues ; everywhere this acid has been
produced by the combination of the carbon with the oxygen,
which in the lung is borrowed from the air, but everywhere
else it comes from the arterial blood. In a word, the oxygen
combined with the blood by respiration, is separated from it
little by little in the capillaries throughout the whole body in
order to produce numerous products, among others car-
bonic acid gas. On leaving the heart and in the arteries,
the blood contains 24 parts of oxygen per 1000, in the veins
it contains only n per 1000. As for the nitrogen and the
vapour of water, one is disengaged, and the other produced
during this same process of nutrition, and both are drawn

96 THE HUMAN BODY.

from the principles in the organism which are introduced into
it by digestion or respiration.

Lavoisier was the first to demonstrate the absorption of
oxygen by respiration, and to show by experiment the analogy
existing between combustion and respiration. " Respiration,"
said he, " is nothing but a slow combustion of carbon and
hydrogen, which resembles, iri every respect, that which takes
place in a lamp. ... In respiration, as in combustion, it
is the atmosphere that furnishes the oxygen. . . . But since,
in respiration, it is the substance of the animal itself, it is
the blood which furnishes the combustible, if animals do
not regularly repair by alimentation that which they lose by
respiration the oil in the lamp will soon be wanting, and the
animal will perish as the lamp will go out for the want of
nourishment." Most physiologists have admitted Lavoisier's
theory, and they consider respiration a slow combustion of
the materials of the blood by the oxygen of the atmosphere,
and as the source of animal heat. We have just seen that this
combustion takes place, not only in the lungs, but through-
out the whole extent of the organs where the arterial blood
carries the oxygen which presides over the phenomena of
nutrition, that is, over the assimilation of the elements of
which the blood is formed, and over the decomposition of
some of these principles of which certain parts only remain
in the system, while others return to be burned in the
capillaries of the lungs, or to be exhaled in the form of gas
or vapour of water.

Some authors again do not admit that combustion takes
place in respiration, the phenomena of which, of quite a dif-
ferent order according to them, may be attributed to a reac-
tion induced by the contact of organized substances. The
decomposition and disassimilation of these are due to a series
of acts of which very little is known, and which are compared
to what has been termed by Berzelius u catalytic phenomena"
But we confine ourselves to a mention only of this doctrine,
which is not generally accepted.

Mechanism of respiration. — We have seen that respiration
is divided into two movements — inspiration and expiration.
In inspiration, the diaphragm contracts and sinks down, push-

MECHANISM OF RESPIRATION. 97

ing the abdominal organs downward. The ribs rise by the
contraction of numerous muscles ; at the same time with the
sternum, which is carried forward, the intercostal spaces en-
large, and the chest is developed in all its dimensions, verti-
cally, antero-posteriorly, and transversely. In expiration, the
inspiratory muscles relax, and others, especially those of the
abdomen, lower the ribs and the sternum by contracting the
chest; while the lungs, distended by the air inspired, collapse
under the pressure of the thoracic walls and their own proper
elasticity. The experiments of Duchenne of Boulogne tend
to prove that this contraction of the lungs is due to the
muscular fibres which accompany the bronchia down to their
minutest ramifications.

Nearly all the inspirations are effected by the movements
of the diaphragm and the inferior ribs only. From time to
time a deeper and more complete inspiration causes the
thorax to rise, not simultaneously but successively at the base,
then at the apex. In the first case the respiration is dia-
phragmatic; when the lower and middle ribs are raised it is
termed lateral; and lastly, when the first rib and clavicle take
part in the movement, it is costo-superior or clavicular. In
diaphragmatic respiration, as M. Mandl has observed, the
larynx is immovable, the inspiration is easy, without effort,
and permits exertion in singing or in gymnastics for a long
time and without fatigue. On the contrary, persons who
respire principally by the upper ribs are easily fatigued, and
very soon out of breath. This is seen in women when the
corset compresses the base of the chest, and in singers who
adopt, on erroneous principles, the bad habit of clavicular
respiration. In this last method of inspiration the larynx is
drawn down by the contraction of the external muscles, and
its action becomes painful. The effort of the inspiratory
muscles rapidly induces fatigue, and the inspiration, always
incomplete, becomes also more frequent. Diaphragmatic
respiration is practised by mountaineers, gymnasts, and skilful
singers — a habit induced either by instinct, or a well-directed
education.

The respiratory movements are not completely under the
control of the will. It is not possible long to suppress the

7

98 THE HUMAN BODY.

contrary movement after an inspiration, and when expiration
has taken place the need of inspiration soon makes itself im-
periously felt. It is impossible, in fact, to retain the breath
except for a very short space of time, two or three minutes
at the longest: the most thoroughly trained divers not being
able to exceed this limit.

Respiratory sounds. — In a normal condition, and when
awake, respiration takes place without noise when the move-
ment is moderate; but when inspiration and expiration are
strong and deep, it is accompanied by a noise caused by the
air passing through the nasal passages or the mouth. During
sleep the column of air breaks against the soft palate and
produces snoring. Besides these sounds, which are exterior
to the chest, there are others produced by the passage of
the air through the bronchial tubes; and when the ear is
applied to the chest of a person in good health, a soft and
regular murmur is heard in rhythm with the respiration; this
is called the vesicular murmur. Several morbid causes
change the nature of this murmur, suppress it, or produce
others. These are so many signs which enable the physician
to determine the condition of the respiratory organs.

Frequency of respiration. — In an adult in a condition of
repose, respiration takes place about eighteen times a minute,
in the infant it is more frequent. As is well known, it be-
comes very active under the influence of bodily exertion, or
under excitement from any cause whether physical or moral.
When, on the other hand, the attention is fixed on a laborious
effort, the breath is held so that it very soon becomes
necessary to take long and deep inspirations to compensate
for the insufficiency of those which preceded. This result
of hard work or great strain of mind should be guarded
against in children, as their constitution suffers greatly under
the influence of incomplete respiration.

Capacity of the lungs. — It is estimated that the lungs of a
man from thirty-five to forty years old will contain about
225 cubic inches of air; it is less before that age, and falls to
a little less than 200 cubic inches at sixty years of age. The
capacity is smaller in women, and varies also according to
the individual. It is only possible to obtain approximate

CHANGES ON THE AIR IN THE LUNGS. 99

experimental results, as the lungs are not completely emptied
at each expiration, and the cells always retain a quantity of
air, and this quantity is greater in proportion as the respiration
is calm and shallow.

Changes on the air in the lungs. — It is clear from the fore-
going, that the air which is expired has neither the same
volume nor the same proportion of constituent elements as
the air which is inspired. In fact, an adult man absorbs by
respiration from 450 to 550 grains of oxygen in an hour.
He exhales in the same time 632 grains of carbonic acid; a
less quantity of nitrogen, amounting to about a hundredth of
the oxygen absorbed; and lastly, about 9720 grains of water
in the form of vapour. This exhalation of water by the lungs
constitutes the pulmonary perspiration, a function analogous
to the perspiration of the skin. The expired air, as already
stated, is deprived of a portion of its oxygen, and is charged
with carbonic acid gas. The proportion of this gas is about
4 parts in 100. From 350 to 400 cubic feet of air are taken
into the lungs in 24 hours, and rapidly changed, and the
gravest consequences result from placing a man under condi-
tions in which the air cannot be renewed. During the Eng-
lish war in India in the last century, one hundred and forty-
six prisoners were shut up in a room scarcely large enough to
hold them, into which the air could only enter by two narrow
windows; and at the end of eight hours only twenty-three
remained alive, and these were in a most deplorable condi-
tion. Percy relates that after the battle of Austerlitz, three
hundred Russian prisoners were confined in a cavern, and
two hundred and sixty of these unfortunates perished in a
few hours from asphyxia.

Influence of the pressure of the atmosphere on respiration.
Mountain-sickness. — It is well known that the density of the
air diminishes with the atmospheric pressure, that is, in the
lower regions of the air, on the sea-coast for example, the
air is denser than in elevated regions. Thus in order to
absorb the quantity of oxygen necessary for sanguification, it
is necessary to respire oftener upon high mountains than
when on plains, but this acceleration of respiration is
perceptible only when the height is considerable and the

100 THE HUMAN BODY.

distance rapidly passed over. Gay-Lussac, who in his
balloon ascension rose to a height of 22,956 feet in six
hours, found his respiration disturbed, and greatly accelerated;
and having made no movement requiring exertion, he could
only attribute this condition to the diminution of the pressure
of the atmosphere. But in climbing mountains the move-
ment and efforts of walking are added to the influence of the
height; and when the difference in altitude in one day
amounts to 6560 feet, a notable acceleration of respiration
and quickening of the pulse is observed, which in many
instances is accompanied by a peculiar sense of uneasiness,
which has been termed mountain-sickness. The most remark-
able symptoms are fatigue or rather partial paralysis of the
muscular system, and especially of the muscles of locomotion.
This paralysis of the legs increases with every step until,
having gone a certain distance with increasing difficulty, it is
impossible to take another step. A rest of a few seconds is
sufficient for the muscles to regain their power, and it seems
as if the traveller could go on without fear of a recurrence of
the difficulty; but very soon it returns, and a fresh halt is
necessary. The higher one goes the shorter the distance
that can be passed without resting — from one hundred and
fifty steps the distance falls-off to one hundred — to fifty — and
at last to twenty or thirty. Inclination to sleep, oppression
of the heart, and loss of spirit are sometimes added to this
periodic exhaustion of strength, and in some persons mountain-
sickness is closely analogous to sea-sickness. In others the
symptoms are such as are always induced in the respiration,
circulation, and in consequence in the muscular system, by
violent exercise. Thirty steps in climbing a high mountain
cause as much fatigue as a forced march or run on a plain.
Respiration, quickened by motion and disturbed by succes-
sive efforts, is no longer sufficient for sanguification; the pro-
portion between the venous and the arterial blood is no
longer normal; and, above all, sanguineous congestion, which
is inseparable from violent exertion, takes place in the lungs,
in the brain, and other organs. But as soon as the muscles
have relaxed for a few moments, two or three full in-
spirations rapidly relieve the congestion, while a flood of

MOUNTAIN -SICKNESS. IOI

arterial blood proceeds from the heart to revive the whole
organism.

Up to a height of 16,400 feet, man can easily acclima-
tize himself to the rarefied air. Baron Humboldt saw Peru-
vians cultivating the land at Antisana, situated 13,454 feet
above the level of the sea; and agricultural labour requires
the development of an amount of force incompatible with
mountain-sickness, even though an energy like that of our
European cultivators may not be found. Jacquemont visited
villages in Thibet at a height of 16,400 feet. La Paz is
situated on the Andes at a height of 12,195 feet, but the
inhabitants suffer no inconvenience from the rarity of the
atmosphere; though strangers can walk only a short distance
without stopping, and they are specially uncomfortable if the
young Peruvian ladies mischievously invite them to a few
turns in a waltz. It is hardly necessary to remark that these
symptoms are not equally urgent in all those who expose
themselves to this rarefied air. Some individuals scarcely
feel them, and are soon acclimatized, while others suffer
greatly for a long period. A host of circumstances and
special conditions contribute also to render these symptoms
more or less marked, and mountaineers themselves some-
times experience them as well as the inhabitants of less ele-
vated countries.

CHAPTER IX.

Circulation. — Organs of the circulation; heart, pericardium; arteries,
capillaries, principal arteries; veins, principal veins ; portal system;
lymphatic vessels and ganglia. — Mechanism of the circulation; dis-
coz'ery of the circulation, action and sounds of the heart, arterial circu-
lation, pulse, capillary circulation; venous circulation, valves of the
veins; discharge of chyle and lymph into the veins. Sanguification;
circulation in the pulmonary artery, capillaries, and pulmonary veins.
— Influences which accelerate or retard the beating of the heart.

Circulation. — The blood is carried by the arteries from the
heart to all the organs, and it returns by the veins from all
the organs to the heart. This movement of the blood to and
from every portion of tire body, from the heart as the point
of departure, is called the circulation. The transportation of
chyle and lymph by the lymphatic vessels, which are the
tributaries and purveyors of the sanguiferous system, is con-
nected also with the circulation.

Organs of the circulation. — The heart is a hollow muscular
organ, nearly in the form of a cone, of which the base is
equal to the height, and about the size of the fist in the
adult. It is situated towards the middle of the chest, a little
to the left (fig. 24, p. 91), and between the pleurae, which
contribute to form its covering. Its apex is directed down-
ward, forward, and towards the left, at about the level of the
fifth rib; its base looks upward, and slightly backward, and
is protected by the sternum. Its anterior face, turned
upward and to the right, is marked by a longitudinal furrow,
as is also its posterior face, which is turned downward and to
the left. Internally the heart is divided by a muscular par-
tition into two nearly equal halves, placed back to back, and

THE HEART.

103

these are each again divided laterally into two cavities, the
superior called the auricle, and the inferior the ventricle. The
auricles take their name from a flattened appendage which

Fig. 26. — Heart and principal arterial and venous trunks.

A. Rigiit ventr'cle.

B. Left ventricle.

C. RigJit auricle.

D. Left auricle.

E. Aorta.

F. Pulmonary artery.

G. Brachio-cephalic trunk.
H. Carotid, right and left.
I, I. Subclavian arteries.
K. Superior vena cava.
L. Pulmonary veifis.

falls down upon their external face. The right auricle com-
municates with the right ventricle, and the left auricle with the
left ventricle. There is no communication between the ven-
tricles, but before birth the two auricles communicate by an
orifice, which is obliterated during the first months of life,

104 THE HUMAN BODY.

leaving as the only trace of its existence a depression called
the fossa ovalis.

The superior and inferior vena cava open into the right
auricle, and at the orifice of the latter is the Eustachian
valve. The orifices of the right and left pulmonary veins
are in the left auricle.

The opening by which the auricles and ventricles commu-
nicate with each other is called the auriculo-ventricular
opening. These orifices are furnished with valves; that on
the right is called the tricuspid valve, from the three angles
which are formed by its leaves; and that on the left is called
the mitral valve, from the slight resemblance which it bears to
a bishop's mitre.

The cavities of the heart are lined by the endocardium, a
very fine, smooth membrane, which has been compared to
the serous membranes. These cavities present numerous
inequalities, which result from the projection of the bundles
of muscular fibre which point in every direction. In the ven-
tricles these fascicles form fleshy columns (columna camece),
disposed in a net-work running from one point of the walls to
another, and several which take part in the movement of
the valves, send out to these valves a crowd of little tendons.
The walls of the left ventricle are much thicker and more
resistant than those of the right ventricle.

Pericardium. — This is the term applied to the covering
which envelops the heart; it is a sac composed of two layers,
a fibrous membrane on the outside, and a serous membrane
on the inside. This last covers the external surface of the
heart, and is reflected back upon itself in order to form, like
all the membranes of this nature, a sac without an opening.
The heart is thus covered by the pericardial sac, but not
contained inside its cavity. A correct idea may be formed
of the disposition of the pericardium around the heart by
recalling a very common and very convenient, though now
discarded head-dress, the cotton night-cap. The pericardium
incloses the heart exactly as this cap covered our forefathers'
heads.

Arteries. — The vessels which carry the blood from the
right ventricle to the lungs, and from the left ventricle to the

ARTERIES.

whole system, are called arteries. The first-named, the rami-
fications of the pulmonary artery, contain the dark blood
which is carried to the lungs to be oxygenized by contact
with the air. It is on the contrary red blood which runs in
the aorta, the original trunk of all the arteries distributed

A-1

Fig. 27. -Transverse section of the heart.

A. Right ventricle.

B. Left ventricle.
C Right auricle.

D. Left auricle.

E. Right auricula-ventricular orifice

and tricuspid valve.

F. Left auriculo-ventriciilar orifice

and mitral valve.

G. Origin of tJie pulmonary artery

and sigmoid valves.
H. Origin of tJie aorta, and valves.
I. Orifice of inferior vena cava.
K. Superior vena cava.
L, L. Orifice of the pulmonary veins.

through the body. There are two classes of arteries, one
pertaining to the pulmonary system or lesser circulation, and
the other to the aortic or general circulation. We will first
consider the last-named.

The ancient anatomists, finding the arteries empty after
death, believed that they were designed to contain air, and
from this circumstance they derive their name (aer, air, and

106 THE HUMAN BODY.

terein, to contain). For the same reason, and with more
accuracy, they named the tube which conveys the air to the
lungs the trachea-artery.

Galen discovered the presence of blood in the arteries,
but he retained the name, and others have continued it,
although it does not accord with their functions.

The walls of the arteries are composed of three superposed
coats. The outer one is nbro-cellular, vascular, and very
resistant; the middle one, the membrane proper or elastic,
is less resistant, and changes its texture under the influence
of age or other causes. The inner is extremely thin, and is
analogous in texture to the endocardium. When a ligature
is applied to an artery, the internal and middle coats are
broken through by the pressure, but the external one
resists it.

The arteries communicate with each other in their course
through the body, and especially toward the extremities by
numerous anastomoses — that, is, they join each other either
by means of branches, or by forming a net-work, the meshes
of which, rounded and in arches, are closer in proportion
as the twigs are smaller. They terminate in innumerable
microscopic ramifications, called the capillary vessels, which
are intermediate between the ends of the arteries and the
veins.

The walls of the arteries are nourished, like all other parts
of the body, by the vasa vasorum, or vessels of the vessels.
And lastly, the arteries are enveloped in their course by
numerous nervous filaments from the great sympathetic
nerve, and by lymphatic vessels.

The arteries which penetrate the substance of muscles,
like those of the thigh and leg, are protected by an aponeu-
rotic sheath, and by fibrous rings which prevent them from
being pulled out of place or compressed during the contrac-
tion of the muscles which surround them.

Principal arteries. — The aorta, which is the main trunk of
the arterial system which carries the red blood, is the largest
artery in the system. It commences at the upper portion of
the left ventricle, not far from the ventriculo-aortic orifice;
it has three valves, called the sigmoid or semi-lunar valves,

PRINCIPAL ARTERIES. 107

which serve to prevent the reflux of the blood, and which
completely close the vessel when expanded.

The aorta runs upward and to the right, and is here the
ascending aorta; then it turns to the left, passing in front of
the spinal column, and taking a new turn downward, it forms
the arch of the aorta; it runs along and to the left of the
spine through the posterior mediastinum, and is called the
descending aorta, and passes through the opening in the dia-
phragm. On reaching the abdomen it becomes the abdo-
minal aorta, up to about the fourth lumbar vertebrae, where
it bifurcates and forms the two primitive iliac arteries.

From its upper portion the aorta throws off important
branches, of which the principal are the following: — The
brachio-cephalic or innominate artery, which springs from the
arch, and is its representative on the right side of the chest.
This trunk gives off the right common carotid and subdavian;
the left common carotid and subdavian spring directly from
the arch of the aorta.

The common carotid arteries run upward along the outside
of the neck on a level with the upper border of the thyroid
cartilage, and each divides into the external and internal
carotid.

The external carotid gives off the superior thyroid, the
facial, lingual, and occipital arteries. At the level of the con-
dyle of the jaw it divides into the temporal and internal
maxillary.

The internal carotid runs upward along the cervical ver-
tebrae, enters the skull, gives off the ophthalmic artery, and is
distributed through the brain.

The subdavian runs outside, behind and below the clavicle,
as its name indicates, and gives off, among other branches, the
vertebral artery, and the internal mammary; and on reaching
the arm-pit (axilla) it takes the name of the axillary artery,
and gives off important vessels to the shoulder and chest;
and then descending along the humerus under the name of
the brachial artery, it divides below the elbow, and forms the
radial and ulnar arteries, which furnish the vessels of the
fore-arm and those of the hand.

Among the arteries arising from the descending aorta we

108 THE HUMAN BODY.

will mention only the coeliac trunk, which divides into three
branches, destined to the liver, the stomach, and the spleen;
the superior and inferior mesenteric, which go to the mesentery
and intestines; and the renal or emulgent arteries.

Iliac arteries. — The common iliac arteries, formed by the
bifurcation of the aorta, run obliquely downward to the
right and left. After attaining a length of about two and a
half inches, each one divides into the internal iliac, which
ramifies on the inside and on the outside of the pelvic
cavity, and the external iliac, which at the point where it
leaves the pelvis gives off the epigastric artery. This artery
runs upward behind the anterior wall of the abdomen, and
unites by anastomosis with the lower extremity of the internal
mammary artery. On leaving the pelvis the external iliac
takes the name of \hzfemoral artery, gives off large branches
to the muscles of the thigh, and on reaching the lower third
of this region, becomes the popliteal artery, or artery of the
ham. This last gives off the anterior tibial, and then divides
into the posterior tibial and the peroneal artery. The anterior
tibial at the point of the articulation of the foot with the leg
takes the name of dorsal artery of the foot, and ramifies over
the upper surface of the foot; while the peroneal and posterior
tibial, after having, like the anterior tibial, distributed branches
to the leg, terminate in the plantar, region, or sole of the foot

Veins. — The veins carry the blood from the extremities to
the heart. They are divided like the arteries into two classes,
according as, filled with red blood, they run from the capil-
laries of the lungs to the trunks of the pulmonary veins —
which is the lesser circulation; or as they carry the black
blood to the venae cavae — which is the general circulation.
The veins of the liver and their principal trunk, the portal
vein, have sometimes been considered as also a separate
system; and this distinction has also been extended to those
of the kidneys and other organs.

The walls of the veins are much thinner than those of the
arteries, and are formed of four tunics, of which the fourth
or internal one is like that of the arteries; the others are
formed of elastic or cellular fibres, longitudinal in the third,
circular in the second, in such a manner as to present the

PRINCIPAL VEINS. IOQ

greatest resistance. The third and fourth coats form folds,
which when extended partially close the vessel. These valves
are disposed in such a manner as that when the blood moves
toward the heart it presses them close to the walls of the veins,
and they are no obstacle to its course; while, if it moves in the
contrary direction, they close and prevent its return toward
the extremities. The veins are disposed in two planes.
Some are deeply placed, and accompany the arteries, of which
they are called the companions (vena comites arteriaruni)\
others are superficial, and creep along under the skin without
any coincidence with the direction of the arterial vessels.
Springing from the capillaries, by means of which they com-
municate with the arteries, the venous radicles unite more
rapidly than those of the arteries into considerable branches,
superior in numbers and total capacity to the arterial trunks.
Many of the arteries, in fact, are accompanied by two veins
as satellites, of at least equal calibre; and the superficial veins
show still greater disproportion. In the interior of the
cranium the veins are transformed into sinuses or canals
formed by the dura mater, which receive the venous branches
of the brain. The veins are enveloped in their course by
numerous lymphatic vessels.

Principal veins. — The superior and inferior vena cava are
to the venous system what the aorta is to the arterial system.

The superior vena cava receives the blood from the head,
neck, the upper extremities, and the walls of the chest; it
opens into the right auricle of the heart. It is formed by the
two brachio-cephalic trunks and the azygos vein. Each of
these brachio-cephalic venous trunks unites, like the arterial
trunks of the same name, all the principal veins of the head
and the arms, which are the two jugulars, internal and ex-
ternal, and the subclavian.

The internal jugular corresponds to the carotid artery; it
receives the blood from the sinuses of the dura mater, from
the veins of the head, of the neck, and part of the shoulder.
The external jugular carries the blood from a part of the
superficial veins of the head to the subclavian vein.

The subclavian vein corresponds to the artery of the same
name, and receives the companion veins, and veins corre-

IIO THE HUMAN BODY.

spending in name to the arteries of the upper limb; it is also
the common trunk of the superficial veins of the hand, fore-
arm, and arm, the principal of which are the cephalic and
basilic. This last vein crosses the radial artery in the bend
of the elbow, and is separated from it by a tendinous expan-
sion of the biceps muscle. The cephalic and basilic veins are
those most commonly opened in blood-letting; this operation
is rendered delicate by the situation of the basilic, which ex-
poses the artery to the danger of being wounded.

The azygos vein (azygos, without a fellow) forms the com-
munication between the superior and inferior vena cava. It
rises vertically in the posterior mediastinum and to the
right of the spine, and about the level of the seventh rib it
receives the lesser vena azygos, which comes from the abdomen.

The inferior vena cava opens into the right auricle under
the superior vena cava. It is the common trunk of all the
veins coming from the parts below the diaphragm, and is
formed by the union of the two iliac trunks, companions of
the iliac arteries; it runs up vertically to the right of the
spine as companion vein to the aorta, and receives the veins
of the abdomen. Its primitive branches, the iliac trunks, are
formed by the union of the veins of the pelvic cavity and of
the lower extremities, companions of the arteries of the same
name. Among the superficial series of veins, which are also
tributaries to the main iliacs, are the external and internal
saphenons veins, which run from the foot to the top of the
thigh. These two veins are plainly visible on the front of
the ankle and on the calf.

Portal system. — An arrangement of veins peculiar to the
abdomen, and especially to the liver, is designated by this
term. The portal vein is formed by the union of the veins
of the mesentery, spleen, stomach, and intestine; it trans-
mits the blood from these organs to the liver, from whence
it is poured into the inferior vena cava.

Lymphatic vessels and ganglia. — This is the name given
to a special circulatory apparatus composed of very delicate
vessels with transparent walls and Q{ ganglia or glands, which
appear to be formed by these vessels, some of which ter-
minate in and others spring from them.

MECHANISM OF THE CIRCULATION. Ill

The lymphatic vessels have a very irregular ^course, and
exhibit numerous swellings which are owing to valves. They
exist in every part of the body, and transport the chyle and the
lymph, drawn by their microscopical roots from the surface of
the mucous membrame of the intestines, or from the tissues
of the organs. They accompany the blood-vessels in their
course, especially the veins, and they are also found in great
numbers at the surface of the body in regions abounding in
subcutaneous veins, as in the limbs, face, and neck. They
are very numerous in the mesentery and around the intes-
tines; they unite in two principal trunks or reservoirs, one
of which is the thoracic duct, which rises through the chest at
the left of the spine, and opens into the left subclavian vein,
the other is called the great right lymphatic vessel (ductus
lymphaticus dexter), which runs parallel with the first, and
opens into the right subclavian vein.

Mechanism of the circulation. — Galen was the first to dis-
cover that the arteries contained blood and that they com-
municated with the veins, but he went no farther than this.
In 1553 Michael Servetus, guessing, so to speak, the pheno-
mena of the pulmonary circulation, indicated very exactly
the course of the blood and its elaboration in the lungs by
contact with the air. But the doctrine of Servetus rested
neither upon proof nor experiment, it resulted from a sort of
intuitive perception of the facts, and he was not aware either
of the impulsive force of the heart or the action of its valves.

Other physiologists, like Servetus, had glimpses of the
truth and added new discoveries to his ; in fact, most of the
phenomena of the circulation had been suspected or indi-
cated at the commencement of the seventeenth century, but
all the knowledge on the subject was but a chaos of facts
and reasonings without unity, and often contradictory. It
required the genius of Harvey to extract from this chaos a
simple and irrefutably demonstrated system.

Movements and sounds of the heart. — The heart, the prin-
cipal agent of the circulation's the source of movements which
are not under the control of the will, but which are constantly
influenced by moral impressions and by sensations. These
movements consist in the alternate contraction and relaxa-

112 THE HUMAN BODY.

tion of the walls of the heart, that is in the opening and
shutting of its cavities. The ventricles contract simultane-
ously, then to this contraction succeeds a period of relaxa-
tion, during which the auricles in their turn contract, to relax
during a new contraction of the ventricles. The dilating
movement is called the diastole, and the contracting the
systole. During the diastole the blood flows into the cavities
of the heart, to be expelled by the systole; the contraction
cf the auricles forces it into the ventricles, that of the
ventricles throws it into the aorta and the pulmonary artery.

The contraction of the ventricles modifies the form of the
heart. Its transverse circumference is ellipsoid during the
diastole, and becomes circular during the systole; the
antero-posterior diameter being thus greater, the point of
the heart strikes the anterior wall of the chest, and if the ear
be applied to this point, a dull sound will be heard at the
moment of the shock, and about half a second after, a clearer
sound is heard, coincident with the relaxation or the diastole
of the ventricles. The mechanism of these sounds has been
variously explained; they seem to be owing, the first to the
sudden closing of the tricuspid and mitral valves at the
moment when the ventricular systole throws the blood into
the aorta and pulmonary artery; the second to the closing
of the sigmoid valves during the ventricular diastole, under
the influence of the elasticity of the arteries, which tends to
cause a reflux of the column of blood.

The alternation of the systole and diastole constitute the
rhythm and regularly marked beating of the heart which
makes itself heard and felt through the walls of the chest.
We will follow these movements in their evolution and the
blood in its course.

Arterial circulation. — The left ventricle, in contracting,
pushes the red blood which it contains in the direction of
the auriculo-ventricular orifice and toward the orifice of the
aorta, — but the mitral valve is so placed that it closes under
the impulse of the moving blood, which is thus forced into
the aorta and from thence into all the arteries, in which its
motion is caused by the triple action of ventricular contrac-
tion, and of the elasticity and contractility of the arterial

ARTERIAL CIRCULATION. 1 13

walls. In vessels of a certain calibre this movement is jerk-
ing and rhythmical, precisely like that of the heart, and if we
place the finger on the course of an artery we feel the shock
of the blood, or the pulse. The pulse and the beating of
the heart are synchronous, that is, they take place simultane-
ously, or rather with an interval so short as to be impercep-
tible. But in proportion as the blood advances through the
arterial ramifications, the numerous changes of direction which
it undergoes and the friction between it and the walls of the
vessels diminish the force of its impulsion; and at last, on
reaching the capillary vessels it flows continuously and with-
out shock.

In examining, under a microscope, a vascular membrane
belonging to a living animal, the circulation of the blood
through the capillaries is plainly visible. The largest of
these canals allow the column of blood to pass rapidly, in
the smallest ones its course is slow and the blood-globules
can only pass one by one; they float in a transparent fluid,
and sometimes a globule becomes entangled obliquely across
the calibre of the vessel and stops until another comes to
push it forward. Malpighi was the first to verify in this
manner the accuracy of Harvey's theory, forty years after it
had been propounded by the illustrious English physiologist.

The different causes, therefore, which accelerate or retard
the contractions of the heart, influence the motion of the
blood in the arteries; and farther, the contractility of these
vessels may be influenced by local causes, and the movement
of the blood is modified so as to be either retarded or
quickened, as they are contracted or relaxed. In the first
case the afflux of blood is not sufficient to excite the organs,
which become sluggish and partially paralyzed; in the second
it is so great as to cause an abnormal activity of the function.
And lastly, we all know that the repose or action of the
muscles has the effect of retarding or accelerating the circula-
tion, general or local, which, in the course of time, results in
the diminution or increase of the muscular strength.

It is in the capillaries, in fact, that arterial blood yields to
the tissues the elements of which it is composed, and which
it delivers to them for assimilation, in order to receive in

3

114 THE HUMAN BODY.

exchange the disassimilated particles which are to be rejected
from the system or submitted to a fresh elaboration. A
living and nourishing fluid, it carries to the organs life, heat,
and the elements of nutrition.

Venous circulation. — After passing through the capillary
vessels, the blood passes into the venous radicles. At its
entrance into the aorta and during its course through the
arterial system, it was of a brilliant red colour, now it has
become dark; the arterial or red blood is changed to
venous or black blood; deprived of the greater portion of
its constituent elements it returns to their source for a fresh
supply.

The blood moves in the veins from the impulsion received
originally from the heart; this force is designated by the term
vis a tergo, because it is exerted behind the fluid column.
The elasticity of the veins, and their contractility also, con-
tributes to urge the blood along in its return towards the
heart, but it is the valves which most effectually second the
cardiac impulse by opposing the reflux of the blood toward
the arteries. If a moderately tight ligature be placed around
the arm, the veins begin to swell because of the afflux of
blood, which can neither go on toward the heart because of
the ligature, nor return toward the arteries because of the
valves which oppose it in that direction. If the finger be now
passed lightly over the course of a vein in a direction op-
posed to the circulation, the little nodules which mark the
projections caused by the distended valves are easily dis-
tinguished. Thanks to the play of these valves, any pressure
upon the veins, from muscular contraction, or whatever
cause, can only carry the blood toward the heart, while with-
out them it would be impelled indiscriminately one way or
the other. Therefore the valves are more numerous in the
veins which are connected with the muscles; in the deep
veins of the limbs, for example, than in those which creep
along under the skin.

Gravitation affects the movement of the venous blood,
which is much less rapid than that of arterial blood. When
the hands hang down for a long time as in walking, they
swell so much that the flexion of the fingers is difficult, and

VENOUS AND PULMONARY CIRCULATION. 115

it is the same with the feet and legs after long-continued
standing, and varicose veins appear on the limbs of persons
whose profession obliges them to remain on their feet.

In following the course of the blood on its return to the
heart, we mid a venous system belonging to the liver and
intestines; the portal system — to which reference has already
been made — which carries the venous blood from the diges-
tive canal and from the spleen to the liver. This system is
remarkable from the fact that it is ramified at both ex-
tremities; at the intestinal extremity the radicles or roots,
and at the hepatic the branches, are found. From this it has
been inferred that the bile is secreted from the blood of the
portal vein and not from the blood of the hepatic artery; but
this question still remains unsettled.

The inferior vena cava, after receiving the blood from the
lower regions of the body, turns toward the heart like the
superior vena cava, but before reaching it, the blood receives
by the subclavian veins the lymph and chyle which have
been brought to it by the two grand trunks of the lymphatic
system; the elements of nutrition drawn from the intestine
come to replace those which have just been given up for
assimilation. Thus partially reconstituted, the blood pours
back through the venae cavae into the right auricle of the
heart, and the auricle by contracting throws it into the right
ventricle.

At last the blood has returned to the heart, and although
it is enriched by the assimilable products of digestion, it is
still incomplete, and must be transformed in order to become
perfect arterial blood, while at the same time the combustion
of a portion of its principles will produce the heat which is
soon to be distributed to the organism. It is in the lungs
that this elaboration of the blood is to take place — hematosis
or sanguification.

Pulmonary circulation. — The right ventricle contracts, and
the flood of venous blood closes the tricuspid valve, and
passes into the pulmonary artery. This artery and all its
ramifications contain black or venous blood, while the pul-
monary veins, as we shall soon see, convey red or arterial
blood ; it is therefore to their direction, from the heart to the

THE HUMAN BODY.

lungs, or from the lungs to the heart, that the vessels of the
pulmonary circulation owe their names. The pulmonary
artery, like the aorta, is provided at its orifice with three
valves, called sigmoid or semi-lunar valves. From the right
ventricle to the ramifications of the pulmonary artery the
blood has but a short distance to pass, and it meets with no
resistance at all comparable to that encountered in the sys-
temic arterial circulation. The walls of
the right ventricle therefore are much
thinner than those of the left, and con-
sequently have less power. In the ca-
pillaries of the lungs the motion of the
blood varies in quickness according as
the respiration is easy, or retarded by
any obstacle, or by the presence of air
unfit for the performance of the respi-
ratory functions. The capillaries are
distributed through the substance of the
lungs in such a manner that they cor-
respond to the pulmonary cells. (See
Respiration, p. 92.) It is in these ulti-
mate divisions of the lungs that the oxy-
gen of the air combines with the venous
blood charged with carbonic acid, and
transforms it into arterial blood. The
reddish-brown globules of the venous
_____ o____^ _._ blood take a vermilion colour from
gram of the course 'of the COntact with the oxygen, and charged

blood in the circulation. . . 1111 •

with oxygen, the blood penetrates into

, ,'. , r -\

the radicles of the pulmonary veins,
obeying the original impulse, the vis a
tergo, as in the general venous system,
but with greater quickness. It is now carried back to the
left auricle, which immediately transmits it to the ventricle,
where its circular course ends, only to commence again
immediately. The circulation may be divided into two
simultaneous periods, or, as has been already stated, the ima-
ginary circle through which the blood passes is composed of
two unequal segments described by the fluid column. The

Fig. 28. — Imaginary dia-
gram of the course of th
ilood in the circulation.

A. Course of the venous
• of

arterial

ACCELERATION AND RETARDATION OF PULSE. II J

upper segment indicates the pulmonary or lesser circulation,
the lower the general or systemic circulation.

Influences which retard or accelerate the beating of the heart.
— In an adult in a normal condition, the heart beats about
sixty times a minute, and the pulse consequently indicates
the same number of pulsations, but diverse causes may
augment or diminish the frequency of these movements.
They become more frequent during digestion, and under the
influence of alcohol, coffee, or other excitants; abstinence,
on the contrary, retards them. Intellectual labour also accel-
erates the action of the heart, but the heart is calmer during
sleep, and shares in a measure the repose of the other organs.
An unlocked for sight, a word striking the ear, or a thought
crossing the mind, will cause strong and rapid pulsations.
Eristratus discovered the cause of the malady which threat-
ened the life of Antiochus, by placing his hand on the heart
of the young prince at the moment that Stratonicea appeared
before him. The pulse is accelerated also by muscular
exercise, and by violent efforts. But in this case the cause
is complex, for the respiration is also more frequent, and this
function is one of those which have most influence on the
circulation. In ordinary breathing, each inspiration gives
more force to the blood in the arteries, and if the respiration
becomes more hurried it is recognizable in the pulse. If, on
the contrary, respiration is suspended or imperfect, the circu-
lation is retarded, and the pulse beats with less force; in a
word, in most physiological conditions there is a constant
relation between the respiratory movements and the beating
of the heart. The alternate expansion and contraction of
the walls of the chest are therefore one of the principal
causes which affect the circulation, by facilitating the afflux
of blood to the thoracic cavity and insuring its expulsion
from it.

The pressure of the atmosphere also influences the beating
of the heart, but only under certain conditions. It is not un-
common to find in the high valleys among the Alps men whose
pulse beats between fifty and sixty times a minute — this infre-
quency is perhaps more common among mountaineers who
live at an altitude of 3280 feet or more, than in less elevated

Il8 THE HUMAN BODY.

countries. We may consider therefore that the altitude has
no influence upon persons who have long lived at a given
level. But if we rise rapidly to a great height, the pulse
quickens very sensibly. Aerostatic ascensions and mountain
journeys furnish the proof of this. It is not to locomotion
or to muscular effort that this quickening of the pulse can
be attributed in the aeronaut or the traveller on horseback,
but it is chiefly due to the greater frequency of respiration in
an atmosphere of lesser density. The diminution of the
pressure of the atmosphere conduces also to the same effect
by relaxing the vessels; but the fall in temperature in pro-
portion to the rise in elevation seems to neutralize this last
effect by the contraction of the tissues which it induces. (See
Respiration, p. 99.)

The establishment of the fact, that an increase in the
pressure of the atmosphere diminishes the frequency of the
pulse is due to the observations of Pravaz and Tabarie. Both
these authors state that the pulse falls to fifty and even to
forty-five pulsations per minute when the subjects are placed
in an apparatus for compressing air, and the pressure is
increased to that of two atmospheres and over. Results
entirely contrary were observed by M. Francois in the tubes
containing compressed air which he used in building the
bridge at Kehl in 1860. This physician observed that the
pulse invariably quickened in the labourers employed upon
this work under a pressure of about two atmospheres.
Other observations by M. Hermel establish the fact that the
pulse is sometimes retarded, and sometimes quickened in
compressed air to one hundred and fifty in a minute. The
phenomena observed in men who work in compressed air
seem to be due to complex causes, among which we must
note the vitiation of the air from deficient renewal.

We shall not here discuss the numerous causes which may,
in pathological conditions, influence the circulation.

CHAPTER X.

Nervous system. — Cerebro-spinal nervous centre. — Cerebrum. — Cere-
bellum.— Isthmus of the encephalon. — Medulla oblongata. — Spinal cord.
— Membranes; dura mater, arachnoid, pia mater. — Nerves; cranial
nerves, spinal nerves, great sympathetic. — Functions of the nervous
system; functions of the spinal nerves of motion and of sensation; func-
tion of the cranial nerves; functions of the spinal marrow. — functions
of the encephalon ; medulla oblongata, pons Varolii, peduncles of the
cerebrum and cerebellum, corpora quadrigemina, pineal gland, optic
thalami, cerebrum and cerebellum. — Functions of the great sympathetic.
• — Reflex pouter. — Nerve force. — Memory.

/ The nervoiis system comprises the cerebrum and cerebellum,
( the spinal cord, and the nerves. It is divided into two por-
tions, the one central, and the other external or peripheric.
The first has received the name of the cerebro-spinal nervous
centre, because it is constituted by the organs which form the

, encephalon and by the spinal cord. The second is the whole
of the nerves proper. Starting from the nervous centre, of
which they are the expansion, they are distributed to the
whole body. They transmit motive or functional impulses
from the nervous centre to every part of the organism; and
the impressions of sensibility from the periphery, that is to
say from the different points of the body to the nervous
centre.

The cerebro-spinal nervous centre appears in the form of a
soft pulpy symmetrical trunk. Its upper portion is an oval
enlargement contained within the cranium, and is called
ths encephalon or brain. The lower portion is elongated
on leaving the cranium in the form of a spindle — it is the
spinal marrow, and is contained in the vertebral canal.
Brain. — This is the term commonly applied to all the

120

THE HUMAN BODY.

Fig. 29.— Cerebro-spinal nervous
centre.

parts of the encephalon, which are
the brain proper, or cerebrum; the
cerebellum, or little brain; the isth-
A mus of the encephalon, or the at-
tachment which joins the differ-
ent parts together; and the bulb
of the spinal cord, or medulla ob-
longata.

The brain occupies nearly all
the cavity of the cranium, which
fits it like a mould. ( It is oval in
form, flattened on its inferior sur-
face, which rests on the base or
floor of the skull; its anterior or
frontal extremity is smaller than
the posteriory Its greatest trans-
verse diameter is the space be-
tween the temporal fossae. It is
divided in the median line by the
great fissure running from behind
forward vertically through part of
its depth into two portions, called
the hemispheres of the brain. This
j division is complete in front, at
/ the back and on the top, but the
/ two parts are united at the middle
and lower third by the corpus cal-
losum, the peduncles, and some
other parts situated in the middle
line.

A lateral fissure, called the fis-

A. Cerebrum-— or brain proper.

B. Cerebellum — lesser brain.

C. Pons l-'arolii.

D, D. Spinal marrow, shoiving the origin

of the spinal nerves.

E, E. Spinous processes of the vertebra.

F. Seventh cervical vertebra.

G. Twelfth dorsal vertebra.
H. Fifth lumbar vertebra.

I. Sacrum.

Fig. 30. — Nervous System.

THE BRAIN. 123

sure of Sylvius, divides each hemisphere obliquely into two
lobes, the anterior and posterior.

The surface of the hemispheres is broken with deep irregular
suld or furrows, which define the oblong rounded winding
ridges, themselves subdivided by secondary furrows, and
called, from their analogy to the windings of the smaller

Fig. 31. — Upper surface of the brain.
A, A. Great fissure. B, B. Cerebral hemispheres.

intestine, the convolutions of the brain. Some of these are
always present, and appear symmetrically in both hemi-
spheres; others are variable, not found on both sides, differing
in length, breadth, and in projection. These convolutions
cover the external, superior, and inferior surfaces of both
hemispheres, and are continued also on their internal surface
the whole length of the great fissure, and of the fissure of
Sylvius.

124

THE HUMAN -BODY.

• The lower surface or base of the brain presents an ex-
tremely complicated relief. In front, and on the sides, there
are numerdus convolutions. Towards the centre we find.

Fig. 32. — Lower surface of the brain.

A. Anterior lobe.

A'. Fissure of Sylvius.
A". Middle lobe.
A'". Posterior lobe.

C. Cerebellum, or little brain.
M<7. Medulla oblongata.
PV. Pans Varolii.
T/. The pitrdtary body.
i-i. First pair, or olfactory nerves.
2-2. Second pair, or optic nerves.
3-3. Third pair, or common motor

nerves of the eye.
4-4. Fourth pair, or pathetic nerves.

5-5. Fifth pair, or trigeminal.

6-6. Sixth pair, or abducent nerves of the

eye.
7-7. Seventh pair —a, Facial nerve.

b, A uditory net ve.

8-8. Righth pair- — a.,. Glosso-pharyngcal
nerve.

b, Pneumo-gastric

nerve. •

c, Spinal-accessory

nerve.
9-9. Ninth pair, or hypoglossal nerves.

among other important details, the olfactory nerves on each
side of the great fissure ; the chiasma, or crossing of the optic
nerves; $h& pituitary body; the tuber cinereum, or ash-coloured
body; the corpora mammillaria, or mammillar bodies; and the

STRUCTURE OF THE BRAIN. 125

peduncles of the brain, which are, as it were, the roots of that
organ uniting it to the .other parts of the encephalon; the
pons Varolii, or annular protuberance; the medulla oblongata;
and the origins of the cranial nerves.

The brain, as well as all the divisions of the cerebro-
spinal nervous centre, is composed of two distinct sub-
stances : the gray or cortical substance, the first on account of
its colour, and the second because it is on the surface of the
brain, like a bark (cortex); and the white substance, which is
everywhere completely surrounded by the gray.

The gray substance is pulpy and less consistent than the
white. It is disposed around the principal organs of the ence-
phalon in a superficial layer, and enters into their substance
in masses varying in form and volume. The white substance
is filamentous in texture, and exhibits, according to the region,
bundles, cords, or layers, composed of slender fibres, which
are alike in the nervous centres and in all the nerves of the
body. The white greatly exceeds the gray substance in total
amount.

On laying open the brain we find it is composed of a
central nucleus — or knot — unique and symmetrical, a sort of
terminal enlargement of the nervous axis, and of two hemi-
spheres united by this central portion, of which they are, as
it were, a sort of double expansion. This central nucleus
comprises parts very complicated in their structure and in
their relative positions. The principal ones are the thalamus
opticus'Qi optic bed, the corpora striata or striated bodies, and
the corpus callosum or hard body. All these subdivisions of
the cerebral centre are united to each other, to the peduncles,
and to the hemispheres. Thus the corpus callosum, which
serves as an envelope of the cerebral centre, receives fibres
from the peduncles and from the optic bed, prolongs its
edges into the substance of the hemispheres, between which
it is, as already stated, the principal means of union.

In the substance of the cerebral centre there are three
cavities, called the ventricles of the brain; two are lateral,
and the third or middle is placed on the median line; they
communicate with each other, and are bathed with a serous
fluid analogous to that which lubricates the spinal cord. On

126

THE HUMAN BODY.

the median line and behind the posterior commissure of the
middle ventricle is a little body nearly conical, which anato-
mists have named the pineal gland or conarium, from its re-
semblance to a pine-cone.

A mass of white substance forms the central portion of

Fig- 33. — Section of the cncephalon in the median line.

A. Plane of the great fissure.

B. Corpus callosum.

C. Optic bed.

D. Pans Varolii, wider which is seen

the medulla oblongata.

E. Spinal cord continued, from the me-

dulla oblongata.

F. Section of cerebellum, showing tJie

"tree of life"

G. Left hemisphere of the cerebellum.

both hemispheres, and this is covered over in every part by
the gray or cortical substance.

The brain is composed then, essentially, of a central
nucleus, and two great lobes or hemispheres. The several
parts of this nucleus differ in their texture, in the proportion
of the gray and white substances, and in the disposition of
these two substances in their tissues; but they all present
fibres which are common to all, which penetrate and unite
them before extending to the two hemispheres.

The mass of the entire encephalon is proportionally greater

WEIGHT OF BRAIN CEREBELLUM. 127

in some species of animals, but none approaches man in the
size of the brain proper. If man holds the first rank in
creation, he owes his position to this admirable instrument
of the soul, to this mysterious medium between the external
world and the thinking being.

The volume of the brain is considerable from the first
stages of existence, and larger in proportion in the new-
born infant than in the adult. It is independent of sex
and of the size of individuals. The weight of the brain in
the adult varies, according to Cruveilhier, from 35 oz. to
52 oz.

The brain is symmetrical, but less constantly so than some
other portions of the nervous centre, and there is often a
notable disproportion between the two hemispheres without
there having been any indication whatever of it during life.
This want of symmetry was very marked in the brain of
Bichat, and this is a striking proof that such a conformation
does not necessarily have an unfavourable influence on the
intellectual faculties, as was thought by this illustrious
anatomist.

The cerebellum or little brain lies in the inferior occipital
fossae, that is to say, in the posterior and inferior portion of
the cranium, and it is covered by the posterior lobes of the
cerebrum. It is an ellipsoid in form, flattened from the top
downward, with its large extremity behind, and its greater
diameter transverse. It is symmetrical, and is composed
of a middle lobe and two lateral lobes or hemispheres.

On the upper surface of the cerebellum is a protuberance,
extending from the front backwards ; it is formed by the
middle lobe, and named from its peculiar appearance the
superior vermiform process. The lateral lobes form an in-
clined plane on either side.

The lower surface fits into the occipital fossae, and forms
two rounded lobes separated by a furrow, which widens in-
front to receive the spinal bulb. About the middle of it is
seen the inferior vermiform process, the lower surface of the
middle lobe which unites the two hemispheres.

The whole surface of the cerebellum is furrowed with
curved and projecting lines, which give it a wrinkled appear-

128 THE HUMAN BODY.

ance (fig. 32, p. 124). These lines or folds are all of about
the same width, and are parallel through a portion of their
course, and then they form acute angles, and are collected
in fascicles, which point transversely downward or backward,
and divide the hemispheres into segments, which are divided
and subdivided into layers.

The cerebellum is composed, like the cerebrum, of white
and gray substance, with the addition of a yellowish substance
interposed in layers between the two others. Each hemi-
sphere is formed of a central nucleus, around which the seg-
ments develop themselves. The layers of these segments
are in juxtaposition like the leaves of a book; the white sub-
stance is in the centre; then comes a layer of the yellow
matter, and over these the gray substance. If we make a
vertical section of the cerebellum, the alternating layers of
the three substances of which it is composed are seen forming
a series of ramifications which spring from a common trunk :
this has been named the arbor vita or tree of life (fig. 33,
p. 126). At the nucleus or knot, the peduncles of the cere-
bellum terminate ; they are three in number on either side,
and serve to attach it to the other parts of the encephalon.
Near the point where these different parts unite, there is a
cavity which is partly circumscribed by the peduncles of the
cerebellum; this is called the fourth ventricle, or ventricle of
the cerebellum. It communicates with the third ventricle of
the cerebrum by the canal of Sylvius.

Isthmus of the encephalon. — This is the term applied to
that portion of the encephalic mass which unites the cerebrum,
cerebellum, and the spinal bulb. It is the point of union of
the three great divisions of the nervous centre. It comprises
the pons Varolii, the peduncles of the cerebrum and cere-
bellum, the corpora quadrigemina, and the valve of Vieussens.

At the base of the encephalon there is a convex projection
which surrounds the peduncles of the cerebrum and cerebel-
lum like a large ring, and which covers the expansions of the
spinal bulb toward these peduncles like a bridge. This is
the pons Varolii, or bridge of Varolius. This projection is
the centre of convergence or of emergence of the nervous
fascicles or bundles which it seems to cover. It is joined to

MEDULLA OBLONGATA. SPINAL CORD. 129

the bulb behind, and in front to the peduncles of the cere-
brum, and on the sides to the peduncles of the cerebellum.
Its inferior surface, which rests on the basilar apophysis of
the occiput, shows fibres running transversely. It is grooved
along the median line, and is perfectly symmetrical.

On its upper face there are four mammillar projections;
these are the corpora quadrigemina. Behind these, and
between the superior peduncles of the cerebellum, stretches
a thin layer of nerve substance, which has been called the
valve of Vieussens, and which forms part of the boundaries of
the fourth ventricle.

The bulb of the spinal cord or medulla oblongata. — This is
the term applied to the enlargement of the upper extremity
of the spinal cord. Pointing upward and forward, its anterior
surface corresponds to the basilar groove of the occiput; pos-
teriorly it rests in a depression of the cerebellum. Although
it is within the cranium, the bulb should be studied at the
same time as the spinal marrow, of which it forms a part.

Spinal cord. — This name is applied to the spinal portion
of the nervous centre. It is a nervous stem, white, cylindrical,
and symmetrical, and lies in, but does not completely fill, the
vertebral canal; it is held in place by the denticulated ligament
at each side. It is united with the encephalon by the med-
ulla oblongata. Terminating in a point at its lower extremity,
it rapidly increases in diameter, and forms the lumbar enlarge-
ment, so called from the region which it occupies; in the
dorsal region it diminishes in size; augmenting anew as it
approaches the neck, so as to form the cervical enlargement,
it shrinks again about the middle of the cervical region, and
then enlarges a third time at its superior extremity, and forms
the medulla oblongata. The spinal marrow is marked in front
and behind, throughout its entire length, by a fissure or median
furrow, which divides it into two distinct halves, excepting a
layer of white substance, which unites both the two fissures
and the medullary fascicles to right and left. This layer,
sprinkled with holes, designed to give passage to vessels, is
the perforated commissure.

The anterior median furrow is covered at the top by the
interlacing of the nervous fascicles which run obliquely from

9

130 THE HUMAN BODY.

one-half of the spinal marrow to the other, and of which we
shall speak presently. The posterior furrow, like the anterior,
disappears insensibly toward the inferior extremity of the
spinal cord; at its upper extremity it opens at an acute angle
where the medulla oblongata commences. Its form re-
sembles the point of a pen — hence the name calamus scrip-
torius which has been given to this part of the medulla
oblongata.

Each half of the spinal cord, separated from the other by
the fissures indicated above, is composed of two cords or
bundles; one, the posterior, giving origin to the posterior
roots of the nerves, and the other, the anterior, to the
anterior roots. These cords are attached to, and are con-
tinuations of, the pyramids of the medulla oblongata.

This latter is marked in front by the median furrow which
extends beyond the interlacing of the fibres, of which men-
tion has been made; on each side of this furrow there is
an oblong elevation, these are the anterior pyramids ; outside
of which are two projections still more marked, called olives
or the olivary bodies. Laterally there is a depression, grayish
in colour, in which terminate the posterior roots of the spinal
nerves; behind this we find a bundle of distinct fibres, the
restiform or cord-shaped bodies ; and lastly, outside of these
bodies are fat posterior pyramids > defining the calamus scrip-
torius on either side. The cerebellum, as we have already
seen, covers the posterior surface of the bulb, to which it is
united by the restiform bodies or inferior peduncles of the
cerebellum, and which contribute with the cavity of the
calamus scriptorius to form the fourth ventricle.

The anterior pyramids terminate by the interlacing of their
nervous fascicles, and this interlacement may be considered
as the lower boundary of the medulla oblongata. These
pyramids are contracted at the apex and at the base, and are
inserted into the pons Varolii by a sort of neck or contraction.

The anterior and posterior roots of the spinal nerves form
two parallel lines on the sides of the spinal marrow. The
roots spring from the spinal cord, but it cannot be ana-
tomically demonstrated that their fibres return to it beyond
the point where they originate and where they constitute by

MEN1NGES OR MEMBRANE OF THE BRAIN. 131

their reunion the medullary fascicles. Opinions are not
fixed on the mode by which union is effected between the
nervous roots and the spinal cord, and we confine ourselves
to the simple statement that the cord appears to consist of
a greater number of nervous fibres than the nerves which
spring from it.

The isthmus of the encephalon is formed by the expansion
of the superior portion of the spinal cord; it is the central
point of the greater and lesser brain, of which the hemispheres
of the cerebrum and cerebellum are but the terminal de-
velopments.

Meninges or membranes. — The three membranes, placed
one above the other, which line the cranium and the vertebral
canal, which envelop the encephalon and the spinal cord,
and extend to all their inequalities, are designated by this
term. They are divided into the dura mater, the arachnoid,
and the pia mater* The name mater, which is given to the
external and internal meninges, appears to have been derived
from the Arabs, who thus designated the covering of any body
whatever.

The dura mater is a resistant, fibrous membrane, which
lines the cavity of the skull and of the spinal canal. It
adheres very slightly to the walls of this canal, but more
strongly to the arch of the skull, and closely to its base.
The arachnoid and the pia mater are interposed between the
dura mater and the nervous centre. It is separated from the
spinal cord by a space filled with the fluid peculiar to the
spinal column ; but it is, on the contrary, directly in contact
with the encephalon, some portions of which it holds in
place.

On the median line of the cranial arch is a triangular
canal, circumscribed by the dura mater, called the superior
longitudinal sinus, which performs the functions of a large
vein. Below this sinus it forms a fold or vertical partition,
which is called \hzfalx cerebri (falx, a sickle), which descend-
ing into the great fissure, separates the cerebral hemispheres.
In its lower border is the inferior longitudinal sinus. Between
the posterior lobes of the cerebrum and the cerebellum the
dura mater covers the latter with the tentorium or tent of the

132 THE HUMAN BODY.

cerebellum, which isolates it from the cerebral lobes. It also
forms the falx cerebelli, which springs from the base of the
skull between the two hemispheres of the lesser brain ; and,
lastly, it extends beyond the cranium, and furnishes the
covering of the optic nerve, and the periosteum of the cavity
of the orbit.

These folds and partitions formed by the dura mater
around and between the organs of the encephalon, serve to
maintain the different parts in place, to prevent their collision
'in shocks received on the body, and to prevent the parts from
falling upon each other in certain positions; as, for instance,
in lying on one side the falx cerebri prevents the weight
of one hemisphere from resting on or compressing the other.
The disposition of the sinuses of the dura mater is not less
remarkable; they are, as already stated, venous canals with
inextensible walls, through which the circulation is easy, and
in no danger from obstruction or suspension ; and when there
is an afflux of blood it cannot compress the brain, as would
be the case if the sinuses were replaced by veins with exten-
sible walls.

Arachnoid. — This membrane has been compared to a
spider's web from its extreme tenuity, and from this it
derives its name. It is a serous membrane, and lines the
dura mater throughout its whole extent. Like the other
serous membranes, it is a sac without an opening, the walls
of which, placed back to back, secrete a fluid. It adheres
very strongly, by its external wall, to the dura mater, to which
it moulds itself, and which it accompanies throughout its
whole extent. Its internal wall is united to the pia mater,
which separates it from the nervous substance at many points.
This union is so intimate that many have thought the arach-
noid has no existence except where it is detached from the
pia mater, as at the level of the fissure of Sylvius, and in the
cerebral sinuses, &c. In fact, the arachnoid does not enter
those intervals where the dura mater does not penetrate, but
is strictly confined to it. At these intervals there is a cavity
between the serous membrane and the nervous centre which
it surrounds, but does not touch, as is well illustrated by the
spinal cord.

PI A MATER. NERVES. 1 33

All the cavities formed by the arachnoid are filled with a
serous fluid called the sub-arachnoid or cerebro-spinal fluid. The
ventricles of the brain also contain, as has been stated, a
quantity of serous fluid. The use of this fluid seems to be
to protect the organs against the effect of blows and shocks.
The brain and spinal cord being, as it were, suspended in
the arachnoid, are held in place in the gentlest possible
manner by the sub-arachnoid fluid, and by that in the ven-
tricles which moistens the surfaces and prevents all friction.

Pia mater. — This is the name given to the membrane
which immediately surrounds the nervous centre. It is a
vascular net-work of extreme delicacy and fineness of texture,
and may be considered as the nutritive membrane of the
cerebro-spinal organs. In its tissue, the arteries running to
the brain are ramified with infinite minuteness, and inosculate
with the radicles of the veins which spring from it. It
follows closely all the cerebral convolutions; penetrates the
furrows, and into the ventricles, and covers even the thin
layers of the cerebellum. It becomes denser and more
fibrous around the spinal cord, of which it forms the neuri-
lemma or envelope, as well as at the origin of the nerves.

To recapitulate, the greater and lesser brain, and the spinal
cord, contained in the skull and spinal canal inclosed in
three superposed membranes, are united by a common
centre, the isthmus of the encephalon. Nerves spring from
the brain and spinal cord.

Nerves. — This is the name given to white or grayish threads
which are attached by one extremity to the cerebro-spinal
nervous centre, and at the other are distributed to the organs.
The nerves are composed of very fine filaments, united at
the point at which they spring from the nervous centre in
bundles called the roots of the nerves; these roots unite and
form the trunks which ramify and disappear, as it were, in
the tissues of the body. A sheath of cellular tissue called
neurilemma or perineurium, envelops the nerves, and pene-
trates between the fibres formed by the union of the nerve-
tubes spoken of in treating of the tissues. The ramifications
of the nerves unite and seem to be confounded at certain
points where they form a very complicated net-work, which is

134 THE HUMAN BODY.

termed a plexus; but this union is effected solely by the
neurilemma. One nerve-fibre — properly speaking — never is
confounded with another. It runs without interruption, and
always distinct, through the most intricate net-work, from the
nervous centre to the organ which it serves. From the
analogy with the union of the blood-vessels, we speak of the
anastomosis of the nerves, and we shall soon see that if the
union of the vessels with each other is an essential condition
of the circulation of the blood, the distinct and absolute in-
dependence of the nerves, even to their minutest ramifica-
tions, is no less necessary to the integrity of the nervous
functions. We may therefore compare the union of the
nerves by juxtaposition during their course to a bundle of
electric wires which, though united, are always distinct,
because of their isolating covering. The isolating covering
of the nerves is the neurilemma.

M. Sappey has recently described, under the name of the
nervi nervornm, or nerves of the nerves, the filaments which
run to the neurilemma, and which stand in precisely the
same relation to the nerves that the nerves themselves do
to the entire organism.

There are two orders of nerves: the one, under the influ-
ence of the will, causes motion in the organs ; these are the
nerves of animal life: the other presides over the functions of
the viscera without our consciousness, and without any effort
of will; these are the nerves of organic life. The first are
cranial or spinal nerves, and spring directly from the nervous
centres, they are white and generally of a resistant texture;
the second, ganglionic or visceral nerves, although connected
with the nervous centre, form a system apart, which is called
the great sympathetic. These nerves are for the most part
soft, and of a grayish colour.

Cranial and spinal nerves. — These nerves are all disposed
in twos, and form a series of pairs to the number of forty,
of which nine pairs are cranial or cerebral, and thirty-one
pairs are spinal.

The cranial nerves are classed as follows : —

ist pair. Olfactory nerves, which are ramified in the
organ of smell.

ENUMERATION OP CRANIAL NERVES. 135

2d pair. Optic nerves, which preside over the organs of
sight. Its terminal expansion forms the retina.

3d pair. The common oculo-motor nerves, which are dis-
tributed to most of the muscles which move the eyeball.

4th pair. Pathetic nerves, so called, because they give the
power of motion to the great oblique muscle, the action of
which, upon the eyeball, is one of the principal elements in
the expression of the face.

5th pair. The trigeminal or trifacial nerve forms on
either side three nerves, the ophthalmic and the superior
and inferior maxillary; they are distributed over the face,
and to the organs which constitute it.

6th pair. The external oculo-motor nerves. These go to
the external straight muscle of each eyeball. The

yth pair is divided into the hard portion or facial nerve,
which goes to the face, and the soft portion or auditory nerve,
which goes to the internal ear. The

8th pair is divided into three branches: i. the glosso-pha-
ryngeal, the nerve of taste, running to* the tongue and pharynx,
and furnishing branches to several muscles of the neck, to the
tonsils, &c. 2. The pneumo-gastric nerve, which branches
out to the cervical region, to the pharynx, the larynx, the
lungs, and the stomach. 3. The spinal accessory of Willis,
which sends branches to several muscles of the neck, to the
pharynx, and to the larynx.

9th pair. The great hypoglossal nerves, which give move-
ment to the tongue.

The spinal nerves form eight cervical pairs, twelve dorsal,
five lumbar, and six sacral. They all spring from the spinal
cord in two bundles of roots, called the anterior and posterior
roots, according to the portion of the cord from which they
emerge. These roots are enveloped in a membranous sheath,
and unite to form the trunk of the nerve at a point more or
less distant from their origin, according to the region from
which they proceed. The roots of the lumbar and sacral
nerves form a bundle of independent cords in the inferior
portion of the spinal canal, which, from their peculiar dis-
position, has been named the cauda equina or horse-tail.

On a level with the openings through which the nerves

136 THE HUMAN BODY.

pass from the spinal canal, the posterior roots form a ganglion
on each side to which the anterior roots unite themselves,
and from which the nerve is distributed to the organism, by
three classes of spinal branches, anterior ', posterior •, and gan-
glionic; the latter unite with the great sympathetic.

The first four pairs of cervical nerves form by the con-
tiguity of their branches the cervical plexus ; the ramifications
of which distribute themselves to the surface, and to the
deep portions of the neck, to the outside of the head, to the
shoulder, and to the upper portion of the back.

The last four pairs constitute the brachial plexus, which,
after furnishing numerous branches to the shoulder and back,
go to the arm as the brachio-cutaneous, musculo-cutaneous,
median, radial, and ulnar nerves.

The twelve pairs of dorsal or intercostal nerves, as well as
the five pairs of lumbar nerves, are ramified in the walls of
the thorax and abdomen, and in the muscles of the back and
loins. The lumbar plexus furnishes, among other principal
branches, the crural nerve, which ramifies into the musculo-
cutaneous of the leg, and the external and internal saphenous
nerves, &c.

The six pairs of sacral nerves are distributed to the pelvis
and to the lower limbs. The first four pairs with the last
lumbar pair form the sacral plexus, the principal terminal
branch of which is the sciatic nerve. This is the largest
nerve in the body; it descends through the posterior portion
of the thigh, to the muscles of which it furnishes several
branches; and a little above the knee it divides into two
trunks — the internal popliteal we tibial, and the external or
peroneal, which distribute themselves by numerous ramifica-
tions to the muscles of the leg and foot.

The great sympathetic. — The nervous apparatus designated
by this name consists of a double cord placed on either side
of the spinal column, the whole length of the neck, and in
the interior of the thoracic and abdominal cavities. It is, as
has ajready been stated, the nervous system of organic, vege-
tative, or nutritive life. Extending from the first cervical
vertebra to the last vertebra of the sacrum, the great sym-
pathetic enlarges at the level of each vertebra, and forms

FUNCTIONS OF THE NERVOUS SYSTEM. 137

nervous ganglia, which communicate by external filaments with
all the cranial or spinal pairs, and constitute by their internal
filaments all the visceral nerves. This string of ganglia gives
the great sympathetic the name of the ganglionic nervous
system.

The great sympathetic forms the pharyngeal, the cardiac,
the solar or coiliac and the hypogastric plexuses. These are
the nervous centres of organic life.

The nerves emanating from the great sympathetic surround
the arteries like a sheath, and penetrate with them into the
organs. Some of these nerves, as has already been stated,
are soft and of a grayish colour, and others are white and
firm.

Functions of the nervous system. — The nervous system is
the seat of intelligence, of sensation, and of motion; it is the
centre of action for the organism, and it presides over all the
phenomena which together constitute life. Its spinal and
superficial portions — the cord and the nerves — take part only
in the functions of sensation, of motion, and of organic life:
but the encephalon contributes at once to the material and
mental functions.

Observers have succeeded in distinguishing in the nerves
and spinal cord the apparatus which is specially devoted to
sensation, from that which presides over motion. But the
knowledge which we have attained concerning the special
functions of the different parts of the encephalon is as yet
very limited, and for the most part hypothetical. Compara-
tive physiology teaches us that some portions are extremely
sensitive and irritable, while others are not affected by-
external agents. The medulla oblongata, the pons Varolii,
and quadrigeminal bodies, are most allied to the spinal cord,
and anatomy can follow thither the medullary fascicles en-
dowed with sensibility, but beyond them these same fascicles
become insensible in the greater and lesser brain, the optic
beds, &c. It appears that after having transmitted the external
impression, they change their nature, becoming an integral
portion of the organ in which the sensation is produced, and
submitted to the apprehension of the intelligence. We are
no less embarrassed if we attempt to specify the portions of

138 THE HUMAN BODY.

the encephalon which preside over motion. As for the seat
of the intellectual faculties, we cannot doubt that it is
situated in the encephalon, but science possesses no exact
data regarding the part played by the different organs con-
tained in the cranial cavity in the elaboration of thought,
and the soul cannot perceive the mysterious tie which unites
it with these organs.

The nervous system, which gives motion and sensibility to
every part of the body, is itself absolutely dependent on the
circulation. It determines ' and regulates its progress by
exciting the action of the heart, but it must itself be excited
by the afflux of blood which the arteries bring to it; and just
as the heart slackens or even stops its action under the in-
fluence of certain impressions, the functions of the brain,
spinal cord, and nerves are inevitably suspended when the
blood does not come to awaken the nervous energy. Any
impediment to circulation of the blood induces paralysis,
more or less complete, in the parts beyond the obstacle, and
no sooner does the nourishing fluid stop its motion, or even
slacken, in. its course toward the brain, than syncope or
fainting supervenes; that is to say, the functions of the
encephalon are weakened or cease altogether.

In giving a summary description of the nervous system,
we have proceeded from centre to circumference, but in
describing the nervous functions the reverse course seems
preferable.

Functions of the sensitive and motor spinal nerves. — Sensa-
tion may be destroyed in a portion of the body while it still
possesses the power of motion, and conversely a limb may
lose the power of motion and still remain sensitive to ex-
ternal impressions. This independence of motion and of
sensation revealed to the physiologists of antiquity the exist-
ence of two orders of nerves, one sensitive the other motor.
Boerhaave and other modern anatomists accepted these
doctrines, on which Lamarck based and promulgated theories
nearly approaching the truth; but Sir Charles Bell was the
first to distinguish, by actual experiment, the nerves of
sensation from those of motion, and to show that they sprang
from two distinct portions of the spinal cord.

FUNCTIONS OF SPINAL NERVES. 139

The anterior fascicles of the cord and the anterior roots
of the nerves which proceed from them are insensible, and
produce muscular contraction. The posterior fascicles of the
cord, and the posterior roots of the nerves, have no motor
power, but they are sensitive. Each spinal nerve, formed by
the union of the anterior and posterior roots, contains sensi-
tive filaments and motor filaments placed side by side in its
trunk and its ramifications. It follows, therefore, that these
nerves and their subdivisions are mixed; as regards the
composition of their fascicles, they are at once sensitive and
motor. They are sensitive to mechanical irritation, and they
excite muscular contraction under the influence of galvanism,
for both these agents meet in the same nerve-filaments
subject to their power. These filaments, separately con-
sidered, come from the centre to the periphery without
division and without anastomosing, in the exact sense of the
word, for what is called anastomosis of the nerves is a simple
juxtaposition, proximity without exchange of their proper
substance, and without intimate fusion.

It is to the continuity of the nervous filaments, and to their
independence, that distinctness of tactile sensation and pre-
cision of motion is due. It is clear, therefore, that if two
sensitive filaments should unite their proper substance, the
impressions perceived by them previous to their union would
be confounded, and would not be referred by the brain to
distinct points. If, for example, two filaments running to
the index and middle fingers, were united, instead of being
simply placed side by side, at any point between the finger-
tips and the brain, they would carry to the brain but one
single sensation for both fingers, and it would be impossible
to tell upon which one the impression had been made. The
result would be the same if two filaments of a motor nerve
running to these fingers were united, instead of isolated in
their proper substance; the motor impulse would be trans-
mitted to both fingers alike, and the brain could not move
either expressly.

In persons who have suffered amputation, phenomena are
produced which are explained by the fact that all the fila-
ments of a nerve exist at its origin which are found at its

140 THE HUMAN BODY.

extremity. The man who has lost an arm or a leg, feels
pains, which he refers not to the stump which remains, but
to the hand or the foot which he has lost. It is the nervous
filaments primitively destined to these parts which are the
seat of the pain, and which now transmit it as coming from
the organ to which they formerly gave sensibility. The same
effect is produced when a piece of skin has been transplanted
from the forehead to the nose by autoplasty; if the patient
be touched on the nose he feels the impression on his fore-
head.

We shall see in treating of the senses, that tactile impres-
sions may be distinct on the tips of the fingers, at a distance
of one-fiftieth of an inch from each other; which implies that
there are two filaments at this interval from each other, running
directly to the brain, but we err if we reckon in this way the
extent of nerve subdivision, for every point in the skin, how-
ever small, is sensitive to the touch. It is by innumerable
ramifications, each of which contains at least one nervous
filament, that the nerves terminate in the organs, those of
motion to excite muscular contraction, and those of sensa-
tion to receive and transmit impressions.

Functions of the cranial nerves. — Like those which spring
from the spinal cord, the nerves of the brain are divisible
into motor and sensory nerves. Among these last some are
endowed with a special sensibility, as the olfactory, the optic,
and auditory nerves; the others transmit general sensations.
Several of the cranial nerves are made up of filaments of
different orders, and are formed by the union of nerves of
general sensation, of special sensation, or of motion. Like
the spinal nerves after the union of their roots, they form
cords, mixed in their functions as a whole, but distinct in
those of their several filaments. The analogy between the
cranial and the spinal nerves is completed by the branches
which go from the cranial nerves of sensation to the great
sympathetic, and by the gray fibres which are seen near the
origin of the cranial nerves, and also near the posterior roots
of the spinal nerves. In the cranium the motor nerves
emerge from the prolongation of the anterior fascicles of
the cord in which the spinal motor nerves originate,

FUNCTIONS OF SPINAL CORD. ENCEPHALON. 141

Functions of the spinal cord. — We have already seen that
the anterior fascicles of the spinal cord are insensitive, and
that they give motor power to the anterior roots of the nerve,
while the posterior portions are sensitive, like the nerves
which emerge from them. These properties of the medul-
lary fascicles were for a long period disputed, but they have
been clearly demonstrated by M. Longet's experiments.
The spinal cord imparts to the nerves of the trunk and limbs
the power of voluntary and respiratory motion. It is also
the source of nervous energy in the action of the heart, and
in the circulation of the blood, in the phenomena of nutrition
and of secretion; lastly, it seems to have only an indirect in-
fluence on the production and maintenance of animal heat.
When there is any lesion of one of the lateral halves of the
cord, it is on the corresponding side of the body that motion
and sensation are disturbed or destroyed. The action
therefore of the spinal cord is direct on the organs to which
it sends nerves, and not crossed like that of the encephalon.

Functions of the encephalon. Medulla oblongata. — The me-
dulla is the central source and regulator of the respiratory
movements. It is in a limited portion of this enlargement
of the cord, near the origin of the eighth pair of nerves, that,
as Flourens has demonstrated, the organ which he calls the
prime mover, or vital node, of the respiratory mechanism has
its seat. This organ, according to M. Longet, does not
comprise all the substance of the bulb, but is only a fascicle,
composed of gray substance between the pyramidal and
restiform bodies. The medulla transmits impressions from
the cord to the brain, and the impulse of the will from the
brain to the cord; its anterior and posterior portions are
prolongations of the corresponding medullary fascicles, and
we may conclude therefore that they share their functions as
they do their substance; and that the medulla by its ante-
rior portion controls movement, and by its posterior portion
sensation. In point of fact, all the nerves which spring from
the anterior portion are sensitive, and from the posterior
motor. The anterior fascicles of the medulla cross their
fibres, and from this results a cross action on the motor
nerves, which originate from these fascicles; the posterior

142 THE HUMAN BODY.

fascicles, on the contrary, do not cross each other, and their
action is direct.

Pons Frtn?///.— -The movements of locomotion are origi-
nated specially, according to M. Longet, in the pons Varolii.
This portion of the encephalon has a cross action on motion.
It is a centre of perception for tactile sensations, but nothing
authorizes us to believe that it can appreciate sensation by
itself alone, and without the aid of the cerebral lobes.

Peduncles of the brain. — These organs unite the greater
and lesser brain to the isthmus of the encephalon, and to the
spinal cord, and seem to be solely devoted to the transmis-
sion of motion and sensation. An injury to one of the
middle peduncles of the cerebellum causes the body to turn
on its axis; a phenomenon which has been variously explained
by different writers.

Corpora quadrigemina, or quadrigeminal bodies. — These
bodies take an essential part in vision, either by inducing
the contractions of the iris, or in contributing to visual per-
ceptions.

Pineal gland. — The hypothesis of Descartes has popular-
ized, so to speak, this organ, whose functions are entirely
unknown. The illustrious philosopher believes the pineal
gland to be "the source from whence the most subtle parts of
the blood, the spirits, flow to all parts in the brain, and are
directed to a particular point, according as the gland is in-
clined one way or the other." This idea of Descartes has
been parodied, by making the pineal gland the seat of the
soul, from whence it directs the impulses of the brain by two
nervous prolongations, called the " reins of the mind "
(habena animi).

The optic beds. — In spite of the name which has been given
them, these portions of the encephalon do not seem to have
any appreciable action on the sense of vision; but they act
upon the voluntary movements in such a manner that the
influence of the right half is felt on the left, and vice versa;
this is called cross action, which is caused, as already stated,
by the crossing of the cerebral fibres. The optic beds seem
to have no influence over the movements of the upper
extremities, as has been thought by several physiologists.

FUNCTIONS OF CEREBRUM. 143

It is unnecessary to enumerate the other portions of the
encephalon, of which the functions are doubtful, or entirely
unknown.

Cerebrum. — Observation has enabled physiologists to dis-
tinguish in the spinal cord and spinal nerves, and even in the
cranial nerves, the sensitive and motor portions; and we must
admit from the results of experiment in comparative ana-
tomy, that certain regions of the encephalon are endowed
with sensibility, while others are insensible; but we have not
yet been able to recognize in the encephalic mass the central
organs, which preside over sensation and over motion. No-
thing authorizes us to think that the insensible portions of
the brain do not take a part in the motor and sensatory
functions, and we are still less able to point out in the en-
cephalon the seat of intelligence. We see the intellectual
faculties develop themselves in the child, at the same time
with, and in proportion to, the development of the brain;
and we know that these faculties continue imperfect, or
changed, when the normal development of the organ is
arrested, and when it suffers from certain lesions; but these
facts, incontestable in principle, have no absolute applica-
tion. The brain may be wounded, and even a portion of it
may be destroyed, without any sensible change in the intel-
lectual faculties; a man of genius may have an ill-developed
brain, as Bichat, for example, whose cerebral lobes were not
of equal volume. On the other hand we see the intellect
clouded under the influence of alcohol, of certain poisonous
substances, or an attack of fever, and no trace is left in the
encephalon of the temporary disturbance ; sleep produces an
analogous effect; dreams are only a succession of false ideas,
a real delirium which ceases on awaking. And, indeed, in
the insane, science can in many cases prove nothing but their
misfortune, of which no part of the brain suggests in the
slightest degree the organic cause. Physiology, therefore, is
very reserved in regard to the cerebral functions, and most
of its theories concerning them are disputed and uncertain.

The cerebral lobes do not seem to be essentially necessary
to the perception of sensitive impressions, general or special.
Thus, pathological observation has established the fact, that

144 THE HUMAN BODY.

vision may be equally good in both eyes, although one hemi-
sphere may be atrophied, or may have suffered, as from
wounds, a great loss of substance. It is, on the contrary,
exclusively in the cerebral lobes that the perception of sen-
sations lies, and that the ideas are formed which these sensa-
tions create. It is also from the hemispheres that the im-
pulse emanates, which results in voluntary motion. Some
physiologists have referred this impulsion to the white, and
others to the gray substance of the brain. Wherever may
be the seat of the motor principle, we know that the brain
exercises a cross action on the muscles; that is, the left hemi-
sphere induces the movements of the right side, and the
right hemisphere those of the left. But in certain cases the
action is direct notwithstanding; this has been explained by
an exceptional incompleteness of the crossing of the cerebral
fibres. Physiologists have sought in vain to localize the
source of motion in the brain, and the difference of opinion
on this point does not permit us to consider it a settled
question.

The encephalon controls the intellectual phenomena, and
most authors consider the cerebral lobes the seat of the soul.
In the superior animals the most complete development of
the brain proper coincides, in fact, with the greatest degree
of intelligence, and the proportions of the brain of man
unite with his intellect in placing an immense interval between
him and animals the most gifted in this respect. And lastly,
the encephalon in idiots is specially characterized by atrophy
of the cerebral lobes, of their convolutions, and of the gray
or cortical substance. Several authors, from repeated observa-
tion of this latter fact, have considered the gray substance
as the seat of the intellectual faculties.

We have already stated, in speaking of the skull, that Gall
and his school have placed the intellectual faculties in the
anterior lobes of the brain, the moral qualities or tendencies
of the mind in the middle lobes, and the animal faculties or
instinctive propensities in the posterior lobes. This doctrine
seems to be the rational consequence of that which recog-
nizes one portion of the encephalon as specially designed for
the functions of the intellect; but if we admit the possible

FUNCTIONS OF GREAT SYMPATHETIC. 145

existence in the brain of distinct and multiplied apparatus in
the explanation of psychological phenomena, it is simply a
hypothesis of which it is out of our power to furnish a single
proof. It is objected, and with reason, to the phrenological
theory, that it groups all the faculties in those portions of
the brain which correspond to the arch of the skull, to the
exclusion of those resting on its base; and besides, patho-
logical anatomy is not in accord with the theory of Gall, and
comparative anatomy does not permit its admission.

The cerebellum. — Among the various functions which physi-
ologists have attributed to the cerebellum, one only has been
generally admitted in latter times; that is the co-ordination
of movement. The repeated experiments of Flourens, con-
firmed by those of MM. Bouillaud and Longet, seem to
prove that the injury or absence of the cerebellum causes a
confusion in the movements similar to that induced by intoxi-
cation, and that this organ is, in fact, the regulator of motion.
Still pathological anatomy does not agree in this respect with
the experiments made upon animals. Perfect integrity of
function, and especially of locomotion, has been observed in
congenital absence of the cerebellum. A great number of
observations made by M. Andral prove that the cerebellum
may be diseased while movements do not cease to be co-
ordinated. The recent investigations of M. Duchenne, of
Boulogne, also contradict the theory of Flourens, and it is
now perfectly well known that the greatest disorder may
exist in the movements without the slightest indication of
lesion in the cerebellum.

Functions of the great sympathetic. — The nervous apparatus
designated by this name is formed, as we know, by the sensi-
tive and motor filaments coming from the cranial nerves, or
from the roots of the spinal nerves. That is, its ramifications
are, at the same time, sensitive and motor. The movements
excited by the great sympathetic are not under the influence
of the will. The motor impulse springing from this system
differs also from that which determines voluntary movements,
in that it travels less rapidly. Experiments upon animals
also prove that the ganglia and ramifications of the great
sympathetic continue their functions some time after they

10

146 THE HUMAN BODY.

cease to be in communication with the nervous centre.
The movements they induce are then executed under the
influence of the nervous force pre-existing, and stored up irr
their substance. The great sympathetic gives motion and
sensation to the machinery of organic life; it controls the
nutritive functions, the circulation, the secretions, &c.

Reflex power. — Besides the voluntary movements which
result from the transmission of impressions by the nerves of
sensation, and from the perception of these impressions,
others are produced in which the will has no part, and which
result from the impulse directly reflected upon the motor nerves,
without any sensation having necessarily taken place, or at
least without our having any consciousness of it. These
are called reflex movements, and the force which determines
them, and is considered as peculiar to the nervous centre, is
called reflex power or the excito-motor faculty. Several physi-
ologists have considered the phenomena classed under the
name of recurrent sensibility as belonging to this reflex action,
but upon the origin of this sensibility authors are not agreed.

Lastly, there is another reflex action which gives rise to
sympathy, that is the particular influence which certain organs
exercise upon others, such as the sensation called setting the
teeth on edge, produced by the grinding of metal against
stone or glass, and the sneezing provoked by tickling the
pituitary membrane, or by snuff, &c. (See Movements, p. 59.)

Nervous force. — The almost instantaneous transmission of
sensation and the motor impulse, by the different parts of
the nervous system, is one of the mysteries of the organism.
This class of phenomena has been compared to those pro-
duced in nature by electricity or magnetism, and the ques-
tion has been raised whether the nervous system is not
under the influence of an imponderable fluid produced in
its substance, or drawn from the same source as all the
elements of animate matter. Various names, such as nervous
fluid, nervous force, the active principle of the nerves, have
been given to the agent whose hypothetical existence permits
us to explain the nervous functions, as we explain the action
of the galvanic pile or the movements of the magnetic
needle. The admirable discovery of Galvani seemed to

NERVOUS FORCE. MEMORY. 147

prove the analogy, if not the identity, of the electric and
nervous fluids. Naturalists and physicians have striven to
establish by the aid of experiment, that electricity is de-
veloped in the nervous centres and circulates in the nerves.
But up to the present time, the most delicate instruments in
the hands of the most skilful observers have failed to detect
in the nerves the slightest electric current, and nothing
authorizes us to consider the nervous force as identical with
electricity. May we not consider them as at least analogous?
They may both be developed by friction, by chemical com-
binations, by heat, &c. ; both are rapidly transmitted, and
both cause an elevation of the temperature, and the composi-
tion or decomposition of certain products. But while it is
true that motor impulses are transmitted with great speed,
comparable to that of the electric fluid, the nervous system
contributes only indirectly to produce animal heat, and nothing
here suggests a current heating a metallic wire. In fact it
is only by hypothesis that we assume the influence of nervous
force on the chemical operations of life, otherwise than in
giving activity to the organs intrusted with these operations.
But we must, notwithstanding, admit a certain analogy
between nervous phenomena and electrical phenomena.
Further research will doubtless throw light upon this ques-
tion, which is so eagerly studied, and which would perhaps
have already been solved if we could compare the reactions
of inert matter to the transformations of organized matter,
and the phenomena which are purely physical with those
in which life takes part.

The memory. — The Greeks made Mnemosyne the mother
of the Muses, and for us, under a less poetical form, me-
mory is the indispensable bond of union of the intellectual
faculties.

The senses reveal to us the external world, the intellect
apprehends the sensations, and rising from material notions
to abstract conceptions, embraces all that man is permitted
to learn or to know; but it is the memory which enables us
to record, as in a book, facts and results, to compare and to
judge, to express thought by language, and to share the
thoughts of others. Without memory man would not recog-

148 THE HUMAN BODY.

nize the ties of blood, of friendship, or of gratitude; the
past would have no existence for him, his life would only
embrace the present moment, and would flow on like the
period immediately succeeding birth. Deprived of experi-
ence, impelled by blind instinct, isolated in creation, he
could not exist with organs which render necessary every-
thing of which he would be deprived. We cannot therefore
imagine the human race without memory, and in order to
find an organization without this faculty we must descend to
the lowest grades of animal life.

Memory is of a compound nature : partaking of body and
of spirit, it is a reflection, an image of ourselves, since it
carries us back to every moment that has impressed our
lives. An exact and enthusiastic historian of the facts which
she recounts to us, she seems to add to our existence the
hours already passed, but as she approaches epochs she
rudely makes us sensible of the flight of time. It may be
happiness that makes us recall hours of pleasure, or in mis-
fortune we may remember them with that pain of which the
poet sings. She shows us the faces of all who have had a
part in our existence, sometimes an isolated portrait, and at
others a crowded gallery; a minute object, a plant, a rock, or
the grandest scenes in nature; a word, or the entire work of
a writer; a fact, or the history of a people. She carries us
back in an instant to the most vivid impressions, or to the
most abstract conceptions, whether of the senses or the in-
tellect. In taking the form of sensation or of thought, she
makes us traverse time and space with a swiftness of which
nothing material can give us an idea; we might indeed say,
that time and space have no existence for the memory, if she
did not in surmounting them awaken the idea of the one
and the other. Obeying the behests of the will, memory
retraces a scientific doctrine as a whole and in detail, the
nicest distinctions of the most violent dispute, the series
of systems of philosophy, all, in a word, that science or
the most profound erudition has been able to classify in the
mind.

We find everywhere the records of extraordinary memories,
great numbers of which come down to us from antiquity.

MEMORY. 149

Mithridates spoke twenty-two languages or dialects accord-
ing to Aulus Gellius, and forty according to Pliny. Scipio
the Asiatic knew most of his legionaries by name; Julius
Caesar, Hortensius, Lucullus, Adrian, and many others, prove
that a powerful memory is not incompatible with a superior
mind. Pic de la Mirandole was a fresh example in the
fifteenth century, as were also Leibnitz and Haller in the
eighteenth. The last-mentioned cites a German, named
Miiller, who spoke twenty languages, and in our day we
have Cardinal Mezzofanti, who spoke nearly fifty, exclusive
of dialects, conversing with the pupils of the College of
the Propaganda, who had come from every quarter of the
globe.

It is related also that Scaliger learned Homer by heart in
twenty-one days, and the other Greek poets in four months;
and we are assured that Magliabecchi could dictate whole
books after having read them once; and if some of these
examples of prodigious memory are not verified, they are at
least rendered very probable by those which are incontest-
able.

It was an extraordinary memory which, enabled the young
Sicilian shepherd, Mangiamele, to calculate mentally with
such rapidity, that the members of the Academy of Sciences
could scarcely follow him even by the aid of the most expe-
ditious processes. But the very ordinary intellect of this
young man proves that in his case memory was a faculty out
of all proportion to the others, a circumstance often observed
especially in children.

Memory is sometimes awakened by a sensation which
carries us back to the time and place where such or a similar
sensation was produced. This memory of the senses acts
upon us with extraordinary power, it is one of the most
effective means which writers possess of touching the human
heart. Eneas wept on beholding a picture on the walls of
Carthage, which recalled the misfortunes of his country.
"En Priamus" Behold Priam! said he, addressing his
companions in exile. Andromache watered with her tears
the grassy mound she had consecrated to the memory of
Hector on the banks of another Simois; and the Florentine

150 THE HUMAN BODY.

accent of Dante made the Ghibeline Farinata forget the
tortures of hell.

In former times the musicians of the Swiss troops in the
service of France were forbidden, under severe penalties, to
play their national airs, and especially the "Ranz des Vaches,"
as it caused the soldiers to desert, or made them home-sick.
Taste and smell are not less powerful in awakening memory,
even after many years have passed.

The seat of memory has been vainly sought in the brain.
Gall and several other physiologists have placed it in the
anterior lobes, and the phrenological school assigns certain
circumscribed portions to the memory of words, of places,
of numbers, and of persons, &c. But this localization is not
justified by observation, and it is no more required by the
memory than by the other faculties. Indeed, the impossi-
bility of attributing to the brain the projections which vary
solely according to the dimensions of the frontal sinus, was
one of the objections to the doctrine of Gall. It is remark-
able, also, that contrary to the opinion of phrenologists, the
greater or less prominence of the eye (that is, the greater or
less depth of the orbit) bears no relation to the development
of the memory. There is more foundation for the observa-
tion of particular aptitudes of memory, specially to retain
words, facts, numbers, &c. We may go still further, if we
observe the changes induced by disease, for in certain cases
the memory fails to retain substantives, or verbs, or other
classes of words only, while all others are retained without
difficulty. We may therefore suppose that certain parts of
the brain are devoted specially to each detail of the memory
as to the other faculties, as to the sensation of every nervous
filament which transmits a tactile impression from any point
of the body. This almost infinitesimal division of the brain
will not astonish us in view of analogous facts derived from
observation, or which reason imposes upon us, although no
material demonstration is possible; yet we must also admit
that the brain, as an organ of apprehension, acts as a whole,
and that if a distinct apparatus exists for the memory, its
action is at once single and multiform, each of its parts re-
ceiving with equal aptitude the impression of the ideas which

MEMORY. 151

are assigned to it. Is it not thus that the innumerable
divisions of the retina perceive with equal distinctness
degrees of light? and is it not rational to suppose that it is
the same with the region of the brain, 'which receives the
nervous filaments which spring from every portion of the
retina?

Very feeble in the first stages of life, the memory is deve-
loped along with the cerebral convolutions, and the gray or
cortical substance. It loses its facility as mature age succeeds
to youth, and retains with more difficulty the facts confided
to it in proportion as years accumulate. In the aged it
retains the impressions acquired during the first half of life,
though in some fortunately endowed organizations it con-
tinues to increase its stores. Cato learned Greek in his old
age; and Baron Humboldt at fourscore embodied in his
Cosmos the whole circle of the sciences, and their most
recent discoveries.

CHAPTER XI.

Sense of sight. — Organ of vision. — Globe of the eye; sclerotic; cornea;
choroid ; ciliary ring ; ciliary body; ciliary process; iris; pupil; nvea;
pigment; retina; vitreous body; hyaloid membrane; crystalline; anterior
and posterior chambers; aqueous humour. — Muscles of the eye. — Con-
junctiva.— Eyelids, eyelashes. — Lachrymal apparatus. — Vision ; func-
tions of the retina, reversed images; functions of the iris; optic centre,
visual angle, visual impressions, single or mixed, adaptation of the eyt to
distances, myopia, presbyopia; achromatism; single and double vision
with two eyes, stereoscope; alternation in the action of the eyes; persist-
ence of impressions on the retina; accidental images; irradiation; acci-
dental aureola; Daltonism; apparent motion of objects. — Optic nerve. —
Movements of the eye. — Extent of vision.

Organ of vision. — The visual apparatus consists of the
globe of the eye and its appendages, which are the eyelids
and eyebrows, the motor muscles of the eye, and the lach-
rymal apparatus.

The globe of the eye. — The globe of the eye is generally
described as a spheroid, to which the segment of a smaller
sphere is applied in front, and this definition is exact to the
senses if it is not so mathematically. The walls of the globe
of the eye are formed principally of two fibrous membranes;
one white and opaque — the sclerotic (sderos, hard)- — which
envelops the two posterior thirds of the globe; and the other
transparent, and resembling a horny plate, from whence its
name, cornea. The sclerotic is one of the strongest fibrous
membranes in the body; it is white on its external surface,
and of a brownish-red colour internally; it is thicker at the
posterior portion of the eye, where it opens to allow the pas-
sage of the optic nerve, than in front, where it terminates in
a circular hollow or slope, into the border of which the cornea
is set like a watch-glass. The two membranes are united by

CHOROID.

153

intimate adherence, so strongly as to seem but one. The
cornea is thicker than the sclerotic, and is composed of
superposed layers perfectly translucent; it is convex in front,
and concave behind, and appears to be circular, although its
transverse diameter is a little greater than the other.

Choroid. — On the internal surface of the sclerotic is a vas-

Fig. 34. — Vertical section of the eye on the median line.

A. Cornea.

B. Anterior chamber.

C. Pupil.

D. Iris.

E. Crystalline.

F. Zone of 2 'inn, forming the an-

terior •wall of canal of Petit.

G. Ciliary processes and circle.
H. Sclerotic.

I. Choroid.
K. Retina.
L. Vitreous body.
M. Optic nerve.
N. Right inferior imtscle.
O. Right srtperior imtscle.
P. Leitator muscle of eyelid.
Q. Lachrymal glands.
R. Lachrymal canal.

cular membrane called the choroid, which lines it closely
from the bottom of the eye to the circumference of the
cornea, and is attached to it by a very fine cellular tissue.
The choroid is composed of two layers, of which the external
corresponds to the sclerotic, and the internal, or membrane

154 THE HUMAN BODY.

of Ruysch, corresponds to the retina. These two layers,
attached to each other by their internal surfaces, are covered
externally with a layer of pigment, which is thicker next to
the retina than on the side toward the sclerotic. The choroid
is pierced behind by an opening, which gives passage to the
optic nerve; in front, near the circumference of the cornea,
it separates in order to form the ciliary circle and ciliary
processes. The ciliary circle, ring, or muscle, is a little band,
vascular, like the choroid, slightly adherent by its external
surface to the sclerotic, and united by its lesser circumference
to the cornea, at the point where the latter attaches itself to
the sclerotic. Behind the ciliary circle a series of membran-
ous rays are seen joined together, and forming a crown;
these are the ciliary processes (from processus, prolongation,
ray), the whole of which constitute the ciliary body or disk.
These rays, which are attached to the choroid, like the ciliary
circle, are of two kinds; one into which the crystalline is
set, and which gives attachment to its capsule, termed the
ciliary processes of the vitreous body; the others extend to
the iris, behind which they form a sort of circular curtain, by
folding back on themselves, and adhering to the larger cir-
cumference of this membrane. Thus fixed by one border,
the ciliary disk floats by the other, like a fringe behind the
iris, yielding to the slightest impulse which may be com-
municated to it. The ciliary processes are covered with a
thick layer of pigment.

Iris. — In the space between the ciliary circle and the
ciliary process the larger circumference of the iris is fixed.
This is a muscular membrane, according to some writers, and
vascular according to others, forming a vertical partition
behind the cornea. The iris is pierced in the middle by a
circular opening called the//////. It represents exactly what
is called a diaphragm in optical instruments. Its anterior
surface is coloured in different shades according to the indi-
vidual, but always remarkable for their delicacy or their
intensity; the variety of which has given to the membrane
the name of iris, or the rainbow. Its posterior face is
covered with a layer of pigment, which is called the uvea.

It is well known that the pupil dilates in the dark, and

IRIS. RETINA. 155

contracts on the contrary in a bright light, only allowing
that quantity of luminous rays to enter the eye which is neces-
sary to vision. Certain substances also when taken into the
system act similarly on the iris; such are opium and the
Calabar bean, which cause the pupil to contract; belladonna,
on the contrary, dilates it. Changes in the diameter of the
pupillary opening also result from certain affections of the
eye and brain. Physiologists consider the dilatation and
contraction of the pupil as belonging to muscular move-
ments; in fact the microscope demonstrates the existence of
muscular fibres in the iris; it contracts also under the influ-
ence of electricity.

It has been remarked that the posterior surface of the iris,
the ciliary processes, and the choroid were covered with a layer
of pigment. This name is also given to a dark brown substance,
appearing black in a mass, which colours certain portions of
the skin in the white man, and the whole tegument of the negro.
In the eye this pigment plays the same part as the lamp-black
in the interior of certain optical instruments, as the telescope
and magic-lantern; it absorbs the luminous rays, and prevents
them from being reflected, which would confuse the vision.

Retina. — The internal surface of the choroid, or rather the
pigmentary layer which covers it, is lined by the retina, a
nervous membrane, upon which the objects are depicted
that we see. It appears to be formed by the expansion of
the optic nerve, which enters the eye at its posterior part,
and forms at the bottom of the globe an enlargement, which
is called the papilla of the optic nerve. The retina develops
itself from the papilla, around which it forms a fold, and ex-
tends over the cavity of the eye to the circumference of the
ciliary processes of the vitreous body, where, according to
Cruveilhier, it abruptly terminates. It is of an opaline white
colour, semi-transparent, and easily torn. Its centre, which
corresponds to the antero-posterior axis of the eye, is to the
outside of the papilla of the optic nerve, where there is a
yellow spot (macula luted) and a depression (fovea centralis).
The yellow spot seems to be the point in the eye where
vision is most distinct. Microscopists describe the retina as
being composed of five, or even eight layers, of which the

156

THE HUMAN BODY.

external one is vascular, and in contact with the choroid; the
internal one, very important in a physiological point of view,
is the membrane of Jacob. It is composed of cylinders, or
rods, joined together like the stakes of a palisade, perpendi-
cular to the plane of the membrane, and forming by their
free extremities a mosaic, each microscopic division of which

Fig. 35- — Rods of Jacob under the microscope.

A. Rods of Jacob. D. Points of the retinal mosaic receiv-

B. Their extremities forming surface of ing different luminous rays.

retina. E. Points receiving each two different

C. Retinal mosaic formed by the rods. rays.

is about o'ooi of a line in diameter according to Robin,
and 0*0008 of a line according to Helmholtz; and repre-
sents a section of a rod. We shall see what part these ter-
minal points play in vision.

Vitreous body. — The cavity of the globe of the eye in its
three posterior quarters is occupied by a substance completely
translucent, the vitreous humor. According to most anatom-
ists, it is contained in an envelope called the hyaloid mem-
brane. The vitreous humor and the hyaloid together consti-
tute what is called the vitreous body, which is perfectly adapted
to the retina throughout its whole extent, and in front takes
the form of the posterior surface of the crystalline. According
to those anatomists who admit the existence of the hyaloid,

CRYSTALLINE. CHAMBERS OF THE EYE. MUSCLES. 157

it folds back on a line nearly corresponding to the border of
the crystalline, and is continuous with the ciliary zone of
Zinn, or the ciliary processes of the vitreous body; this zone
embraces the border of the crystalline, around which it forms
the cajial of Petit, and adheres intimately to its capsule.

Crystalline. — This is the name given to a double convex
lens, more curved posteriorly than anteriorly, translucent,
and placed vertically in the axis of the eye, so that the axis
of the lens corresponds to the centre of the pupil. The
crystalline is formed of superposed layers, which are less con-
sistent outside than towards the centre; it is contained in a
capsule, which applies itself closely without adhering to it.
The greater or less convexity of the surfaces of the crystalline
modifies the power of the eye, determining whether the vision
is long or short, i.e. presbyopic or myopic. The opacity of
the lens, or of its capsule, forms the disease called cataract.
We have already stated that its edge is set into the zone of
Zinn, to which its capsule adheres.

Anterior and posterior chambers of the eye. — Formerly a
certain space was supposed to exist between the crystalline
and the iris ; this was called the posterior chamber of the eye.
We now know that the posterior surface of the iris is in
direct contact with the anterior surface of the crystalline, and
the posterior chamber is only an imaginary space. The
interval which divides the iris from the cornea is the anterior
chamber, which is filled with a fluid called the aqueous humor,
translucent like the vitreous but less dense ; it is secreted by
the ciliary processes.

Muscles of the eye. Conjunctiva. — The globe of the eye is
situated in the anterior portion of the orbit, beyond which
it extends, and its axis, which is on the plane of that of the
orbit, is directed inwards towards the centre of the base of the
cranium. The eye is fixed in the orbit by an aponeurotic
capsule, the optic nerve, and by six muscles which turn it
in every direction. A mucous membrane, the conjunctiva,
so named because it unites the eye to the lids, spreads over
the anterior portion of the globe, as is proved by the injec-
tion of its vessels in some ophthalmic affections, and then
folds back on itself, and lines the internal surface of the eye-

158 THE HUMAN BODY.

lids. According to some anatomists, it is not the conjunctiva,
but only an expansion of its epithelium, which covers the
cornea.

Eyelids. — An elliptical muscle extends in front of the
orbit, which is formed of concentric fascicles, and which
presents a transverse chink closed during contraction, and
open in the shape of an almond when its fibres are relaxed.
This is the orbicular muscle of the eyelids. Its ocular surface
is covered by the conjunctiva, its external face by the skin, its
opening is circumscribed by the edge of the lids, which are
made firm by the tar sal cartilages. The upper lid is larger than
the lower, and is raised by a special muscle, the contraction
of which alternates with that of the orbicularis, which is its
antagonist. The points where the eyelids are united by their
commissures are called the angles of the eye. At the internal
or greater angle of the eye, the conjunctiva forms a fold,
the semi-lunar fold, which is in fact a rudimentary repre-
sentative of the third eyelid (membrana nictitans) of certain
animals. Inside of this fold is the lachrymal caruncle, a
small glandular body of a rose colour, which is covered by
the conjunctiva. The edges of the lids are ornamented with
a fringe of silky hairs which protect the eye, and add greatly
to its beauty. The greater or less extent of the opening of
the lids makes the eye appear larger or smaller; the confor-
mation of the palpebral muscles and the tarsal cartilages gives
to the eye an elongated and languishing form as in the East,
or round and bold as among the Occidentals; but the dimen-
sions and form of the globe are the same in all countries and
in all individuals.

The upper lid, which is attached to the arch of the orbit, is
surmounted by the eyebrow, which is designed to protect the
eye like a visor, and its movements play an important part
in the expression of the face.

Lachrymal apparatus. — This is composed of, firstly, the
lachrymal gland, which lies in a depression of the orbital arch,
and of little glands of the same nature, which form a granular
layer in the substance of the upper lid; secondly, of the lachry-
mal canals, by which the tears are poured out upon the con- ,
junctiva, a little above the border of the upper lid; thirdly ',

TEARS. VISION. 159

the lachrymal ducts, which are destined to receive the tears
after they have bathed the eye, and of which the orifices or
lachrymal points are seen near the internal commissure of the
lids; fourthly, the lachrymal sac, in which the lachrymal
ducts terminate, and which empties the tears into the nasal
canal.

The tears by running over the surface of the conjunctiva
render it supple and facilitate the movements of the globe
and eyelids by lessening the friction. They serve the same
purpose in the eye as the synovia does in the articulations.
The influence of moral or physical causes increases their
secretion, and the lachrymal ducts do not suffice to carry
them off when they run over the lids.

Vision. — Among the phenomena, all of which constitute
the sight, some belong to the domain of physics, and may
be submitted to investigation, many may even be demon-
strated by experiment; while others, on the contrary, are
patent to the observation, but little known as to their cause
or their mechanism, and await from the progress of science
an- explanation which physiology has as yet been unable to
give. Even in those phenomena which at first seem purely
physical, we must not forget that the refracting media of the
eye are organized, and cannot be compared except by
approximation to inorganic bodies, on the form and density
of which physicists base their calculations. This is necessarily
the cause of the differences in the theories promulgated in
regard to vision; for although the eye may in some respects
be considered as an optical instrument, we can never arrive
at exact deductions by comparing organs analogous or even
similar in their construction, but different in their nature.

Physicists claim as belonging to their proper province the
visual phenomena produced between the cornea and retina;
everything on the other side of that membrane belongs to
physiology.

The retina renders the eye sensible of light, and we may
therefore consider it as the essential organ of vision. The
function of the other portions is to convey the luminous rays
to its surface under conditions necessary to a nervous im-
pression, which all combine to insure, but which is accom-

l6o THE HUMAN BODY.

plished in the retina alone. Other causes besides the contact
of luminous waves may excite the retina; thus the pressure of
the finger on the eye for example, and the disturbance re-
sulting from a fall or a blow on the head, the action of elec-
tricity, and certain affections of the eye and brain, give rise,
in the absence of natural or artificial light, to luminous
images varying in form and intensity. Light produced
under these conditions is called "retinal light."

Like the optic and the other special nerves of the organs
of sense, the retina has a special sensibility; it receives the
impression from the light and transmits it to the brain, but it
is not itself sensitive to touch. No mechanical irritation
causes it the slightest pain. In a normal condition, the action
of a too brilliant light, and in certain affections of the eye
and brain, the least ray will cause a painful sensation, but
this pain must be referred either to the encephalon or to
the nerves of the iris or of the ciliary circle, independent of
the retina and the optic nerve.

Punctum cctcum or blind point.— Mariotte was the first to
recognize that all parts of the retina were not equally sensi-
tive. According to most authors, a limited portion of this
membrane, corresponding to the papilla of the optic nerve,
is totally insensible to light. M. Longet admits that there
it has, at any rate, a very obtuse sensibility. This "blind
point" is the only one on the internal surface of the eye
which is not covered with pigment.

If we trace two figures on a horizontal line on a piece of
paper placed vertically (fig. 36, p. 161), and then shut the
right eye, and fix the left on the right figure, at certain dis-
tances we can see both of them more or less distinctly; but
varying the distance of the paper from the eye, there is a point
when we only see the figure upon which the eye is fixed ; the
other disappearing entirely, but it reappears when we change
the position of the paper, or cease to look fixedly at one figure.
The greater the distance between the two figures, the greater
must be the distance of the paper from the eye, in order to
render one of them invisible. The image of the invisible
one is then projected on the blind point, and it reappears,
when by the displacement of the paper the angle which its

ENTOPTICS. REVERSED IMAGES.

161

rays form with those from the other becomes more or less
open.

Ent optics. — The eye perceives not only external objects, but
certain details of its internal organization.
This portion of the visual phenomena is
called interior vision, or entoptics. A
bruise of the cornea through the lids, or a
scar or foreign body on its surface, the
vascular ramifications of the retina, and
other causes of that nature, sometimes
throw images on the retina of different
forms, such as striae, spots, globules, dark
or luminous circles which appear to move
in the eye. Certain of these images are
called ilies, or motes (musccR voliiantes\
because they traverse the field of vision
from one side to the other. Their ap-
pearance results from nothing abnormal,
and they cannot be confounded, when
there is no other disturbance of the visual
functions, with the analogous signs which
accompany and denote some diseases of
the eye and brain. A. lateral movement
of the eye is sufficient to displace them or
cause them to disappear.

Reversed images. — The eye may be
compared to an optical instrument known
as the camera obscura. It is well known
that the image of objects appears re-
versed on the screen of the camera; in
the same manner the luminous rays which
spring from every point of an object at
which we look, traverse the cornea, the
aqueous humor, the crystalline, and the Fig. 36.

vitreous body, in order to reach the re-
tina ; and are refracted in this transit, so that the image which
they form appears reversed at the bottom of the eye. In
examining the eye of an ox, of which the sclerotic has been
previously made thin — or the eyes of albinoes, such as white

11

1 62 THE HUMAN BODY.

rabbits, for example, which are destitute of pigment, and in
which the sclerotic and choroid are transparent, we may see,
as Magendie pointed out, the flame of a candle reversed upon
the retina.

How then are we able to see objects in their real position?
BufTon and others have asserted that reason enables us to
restore the image depicted on the retina to its real position,
that touch enables us to rectify the visual sensation. But
Cheselden, having by an operation enabled a patient born
blind to see, does not state that the young man first saw
objects otherwise than in their real position; and the careful
observations made by this skilful surgeon do not permit us

Fig. 37. — Course of the luminous rays in the eye.

H, M, P. Luminous rays emanating from an object,
h, m, p. Lviminous rays refracted, forming the inverted
image on the retina.

to suppose that a circumstance of such importance could
escape his notice. According to M. Lame, we know that
objects are upright although we see them inverted, from the
consciousness of the movements which we give to the optical
axes of our eyes in looking successively at the different
points of objects from top to bottom.

Miiller avers that we see the objects inverted, but that all
presenting themselves to us under the same relative condi-
tions of position, nothing can appear inverted because we
see everything in the same position, and that our notions of
uprightness or inversion only exist by opposition.

THEORY OF UPRIGHT VISION. FUNCTIONS OF IRIS. .163

M. Longet explains upright vision by supposing that every
external luminous point is felt in the eye according to the
direction it takes relative to us. We must, says this eminent
physiologist, consider the concave spherical surface of the
retina as formed of a mosaic, each elementary part of which
is a sort of eye designed to perceive the different luminous
impressions in a determinate direction. Every pencil of
light emanating from a luminous point, and forming a cone
of which the apex and the normal axis correspond to one of
these portions, will be perceived in the direction of a line
joining the centre of the spherical surface to the object
looked at. If we reason in this way for every one of the
points which constitute the whole of a visible object, the
perception of each of these points will be in the real direc-
tion, and that of the whole will also be felt under the same
conditions, in regard to the observer. The image therefore
is not seen as a complete whole ; each luminous point assist-
ing in its formation milking a separate impression on the
brain, each one is felt according to the primitive direction of
the ray of light, and the whole is seen in its real position.

Functions of the iris. — In order that vision may be distinct,
it is necessary that the rays should enter the eye in the
direction of what is termed the visual axis, and the various
movements of the organ tend unceasingly to place it in a
position to fulfil this condition, and it is necessary, also, that
the light should be neither too strong nor too weak, and that
the rays shall traverse the central portion only of the
crystalline, and not its borders. In order to obtain an
analogous result in some of their instruments, opticians
divide them by means of a partition pierced by a hole in
the centre, which is termed a diaphragm. We find a similar
arrangement in the eye, " an intelligent diaphragm," to use
the expression of M. Longet, that is the iris, which dilates
or contracts the pupil in such a manner as to measure the
quantity of light necessary to vision, and which only allows
those rays to pass which are directed toward the central
portion of the crystalline lens. In the dark, or if we look at
an object but slightly illuminated, the pupil dilates in order
to admit the greatest possible number of rays which are

164 THE HUMAN BODY.

refracted by the cornea; it is the same if we look at a
distant object, the rays from which are less divergent; if this
object becomes more luminous, or if we approach it, the
pupil contracts in proportion.

Optic centre, visual angle, appreciation of the size of objects.

—The rays emanating from two points of an object, p H (fig.

38), converge toward the optic centre o, at a point in the eye

a little behind the crystalline, and thus form an angle P o H,

which is called the visual angle. From the optic centre these

rays diverge to the retina, and form an angle, / o //, equal to
the first, the base of which, corresponding to the retina,
measures the size of the image which they form upon it. The
visual angle therefore gives us an idea of the size of objects,
and enables us to compare them, but in order that our ideas
may be exact, they must be confirmed by our notions of dis-
tance. In fact, several objects of unequal size, P H, P'H',
P"H", may be placed at such distances, ABC (fig. 38), as to
subtend the same visual angle; we must therefore estimate
their relative distance, in order to judge correctly of their
size. We can also obtain a knowledge of their size, if we know
that of any portion of the object which we see, or the size
of another object placed at an equal distance. Thus, when
we look at a ship at sea, we can judge of its size by that of
the men whom we see upon it; the height of a balustrade
enables us to calculate approximately that of the building of
which it forms a part. When the means of comparison fail

ESTIMATION OF SIZE. VISUAL IMPRESSIONS. 1 05

us, it is very difficult to avoid errors, the very causes of
which escape us. Thus, the sun and the moon when they
are near the horizon, seem to present a much greater diameter
than when high in the heavens. The atmosphere causes
objects to appear near or distant, according as it is pure, or
charged with mist. These illusions are frequent, especially
among mountains, and the inexperienced traveller should not
count too much upon the exactness of his impressions.

Bravais points out a very common error in drawing a
rough hill-side in relief, or a mountainous horizon. In veri-
fying a sketch mathematically, the horizontal distances of
the different points in the landscape are found to be suffi-
ciently exact, while the height of the summits, or of inequalities
of surface, is in double proportion. But we must add, that the
design adjusted mathematically seems incorrect in an opposite
sense, and does not give the impression of the natural relief.

If a rainbow is formed over a cascade when the sun is
near the horizon, and the circle of this bow is nearly com-
plete, we seem to see not a circle, but an ellipse, of which
the principal axis is vertical; the same illusion is produced
when we look at a halo.

Visual impressions, separate or mixed. — If we look at a
print placed at a certain distance, the details of the engraver's
work disappears, the dots and the shading are confounded
with the white lines which separate them, and the eye per-
ceives only a grayish tint more or less distinct; so also, if a
red and blue powder be mingled together, the mixture gives
us the impression of a violet colour, although every grain of
each powder preserves its own proper colour. This is ex-
plained as follows. We have already stated that the internal
surface of the retina presents a mosaic of extremely small
terminal divisions, each one of which acts separately, and
transmits to the brain one single impression at a time. If
the image of a trace of the burin or of a grain of powder
covers one of these divisions, the impression is single (see
%• 35? P- J56); but if two lines, one white and the other
black, or two grains, one red and the other blue, are so
small and so near together, that their images are in juxtaposi-
tion on the same division of the retina, the impression is

1 66 THE HUMAN BODY.

mixed, and the brain perceives the sensation of gray or of
violet. Or, in other words, in order that two minute luminous
objects may be distinctly seen, the angle subtended upon the
retina by their images must not be greater than the diameter
of one of the retinal divisions. The distance of the two
objects from the eye being determined, the measure of the
angle subtended by them enables us to estimate the size of
these divisions.

Accommodation of the eye to distances. — When we make use
of the camera obscura, in order that the image may be dis-
tinct the screen must be placed in the focus of the instru-
ment, that is at the point where all the rays refracted by the
objective converge. If the objects recede or approach, the
screen must be placed at a proportionate distance from the
object-glass, so that its surface may correspond to the apices
of the refracted luminous cones. And yet we see with equal
distinctness the images of objects at very unequal distances,
without any variation in the form of the eye, or the relative
conditions of its media, or at least without our consciousness
of anything but a scarcely perceptible effort. This power of
accommodation of the eye has long been the subject of inves-
tigation, and the question is not yet settled. The most
generally received explanation is, that in order to see objects
at different distances, and especially very near to the eye, it
modifies its form, or that of its media, and adapts itself to the
distance in such a manner, that the retina is always in the
focus. According to some authors, the length of the axis of
the eye varies, the retina approaching or receding from the
crystalline. Others maintain that it is the crystalline which
changes its place, or that the curves of the refracting media
modify themselves in such a manner, as always to make the
apices of the luminous cones coincide with the immovable
retinal surface. This theory of adaptation or accommodation
is denied by some eminent savants, though a few of them
approach it in attributing this phenomenon to the contrac-
tion and dilatation of the pupil; while others have endeavoured
to demonstrate that the distance of objects from the eye may
vary to a great extent, without the image undergoing any
appreciable modification.

ACCOMMODATION. 167

Helmholtz maintains that the anterior surface of the crys-
talline increases in convexity in looking at objects near at
hand, and flattens when looking at a distance; the pupil
contributes also to the accommodation by contracting in
looking at objects near at hand, and dilating to see at a
great distance. Nothing positive is known regarding the
manner in which this change of form in the crystalline is
effected. M. Helmholtz inclines to the opinion that the
diameter of the lens is increased or diminished, and conse-
quently it becomes more convex, or more flattened, accord-
ing as the zone of Zinn, which is inserted into the crystalline
capsule, is distended or relaxed by the action of the ciliary
muscle.

Some simple experiments prove that the eye cannot see
distinctly, without an effort of adaptation, two objects placed
at unequal distances, and that the image distinctly perceived
by the retina when placed in the focus, is so no longer when
the focal distance is changed.

i. If we look with one eye at the heads of two black pins,
placed in a line at the same level, but at different distances, we
shall see one of them distinctly and the other vaguely. If we

Fig. 39. — Accommodation of the eye to different distances.

look at the nearest one the image is perfectly clear, while the
one farthest away is enveloped in mist; but if we look at the
latter we see it easily without change of position, but when its
image is well denned that of the other pin becomes confused.

2. In looking at a pin through a small hole pierced in a
card, we can see either the pin or the edge of the hole dis-
tinctly; but when the image of one is distinct the other is
confused.

3. By making two pin-holes through a card, at a distanc \

1 68 THE HUMAN BODY.

less than the diameter of the pupil, that is, not more than one-
twelfth of an inch from each other, then look through these
two apertures at a small object on a bright ground, at a black
point, for example, on a sheet of white paper. At a certain
distance the point is single, but if the head be moved back-
ward or forward it will appear double.

In the first two experiments the eye is compelled to adapt
itself to the distance, in order to see distinctly and succes-
sively two objects at unequal distances, and of which the
images are not distinct, except when the apex of the cones
formed by the refracted rays of light exactly corresponds to
the surface of the retina, that is, when the retina is exactly in
the focus. And also, the experiment of looking through a
pierced card at an object, and seeing it distinctly, that is,
looking at it through an immovable artificial pupil, seems to
prove that the movements of the pupil are not necessary to
accommodation.

The third experiment proves, that in order to see a single
image the retina must be in focus. In this case, in fact, the
rays coming from the external object converge and meet on
the same retinal divisions, hence there is but a single sensa-
tion; if the eye approaches or recedes, they reach the retina
either before their convergence is effected, or not until,
having converged, they cross each other, and diverge beyond
the focus, in either case in such a manner as to fall upon
different divisions of the retina, and in consequence produce
a double sensation.

The accommodation of the eye therefore seems to be in-
contestable, in spite of the want of accord in the opinions of
savants upon its mechanism. A very little attention enables
us to recognize the effort which accompanies it, especially if
the adaptation is prolonged without variation at a short dis-
tance, as in looking through a microscope. Then, in fact,
the eye loses sometimes for several hours the faculty of
adapting itself to great distances; it becomes myopic for a
certain time. Persons who are in the habit of using a glass
for one eye, as watchmakers and engravers for example, are
generally myopic in that eye; and this effect is very marked
in infants, who acquire the habit of looking at objects near

MYOPIA. PRESBYOPIA. 169

at hand. Short-sightedness is thus much more common in
towns than in the country. Sailors, mountaineers, and in-
habitants of deserts are generally very long-sighted; the
habit of looking at great distances doubtless develops this
faculty.

Myopia, presbyopia. — The range of sight at which we read
or write is, in a normal condition, about 12 to 14 inches;
this point in myopia is much nearer, and in presbyopia
much farther off; but for the latter, distinct vision does not
go beyond 28 to 32 inches, that is, about double the dis-
tance considered normal; in myopia, on the contrary, this
distance may diminish to within an inch. This condition
of the sight is the result of modifications of the media of
the eye. In myopia the cornea or the crystalline is more,
and in presbyopia less, convex than in the normal condition.
In myopia, therefore, the focus is in front of the retina
for objects which, not being very near the eye, send to it
rays which diverge but slightly; in presbyopia, on the con-
trary, the slight refraction caused by the flattening of the
cornea, or the crystalline, tends to place the focus behind
the retina, the point of convergence of rays coming from
objects near at hand. The faculty of accommodation is
rather limited in myopia, as well as in presbyopia, and is
necessarily almost entirely wanting in the very near-sighted.

To remedy these modifications of the eye, the short-
sighted person requires double concave glasses, which increase
the divergence of the rays in proportion to the refraction by
the media of the eye; the long-sighted person requires
double convex glasses, which produce the opposite effect.

It is not uncommon to find persons who can only read
and write at a very short distance, but who can notwith-
standing see objects at a distance perfectly well. In this
case only one eye is myopic, the other is normal. A slight
inequality in the eyes is very common, and often unper-
ceived. This is undoubtedly the reason that many persons
use but one eye even when looking with both, without being
conscious of it, and this inequality, which is either the cause
or effect of this exclusive action, can only be augmented
by it.

1 70 THE HUMAN BODY.

Short-sightedness, even when slight, is an infirmity from
which its subjects suffer all their lives, and it may be aggra-
vated by the use of too strong glasses, and, as we have
already stated, by the use of the microscope. Long-sighted-
ness, on the contrary, does not make itself felt much before
the age of forty, and then only in persons whose sight is
good. It is, as the name presbyopia indicates, a mark of
age, and a little philosophy enables us to resign ourselves to
it, and wear the glasses which were useless in youth.

Achromatism. — In ordinary vision objects appear to us in
their natural colours distinctly defined, and not surrounded
with the iris-like fringe which results from the decomposition

Fig. 40.

<7, a. Globes of the eye.
bb, b' b' . Objects placed in front of or beyond the point of convergence of

tJie two axes,
c. Point of convergence.

of light. It would seem therefore that the eye is achromatic.
But the experiments of Arago, Frauenhofer, and other scien-
tific men, prove that it does not absolutely possess this pro-
perty, though it is only when placed under abnormal condi-
tions that we discover this. If, for example, we look at an
object, and adapt the eye to an imaginary point, either in
front of or beyond it, the image both becomes indistinct,
and its edges become rainbow-like. If a body is placed
near the cornea, in such a way as to cover a portion of the
pupil, the same effect is produced.

Single or double vision with two eyes. — Although a separate
image is produced in each eye when we look at an object,
the object appears single under normal conditions of the

SINGLE VISION WITH TWO EYES. STEREOSCOPE. 171

sight, that is to say, when it is placed at the point at which
-the optical axes converge; but if the direction of one of
these axes is changed, from pressing lightly with the point of
the finger on the external angle of one of the eyes, for in-
stance, the object appears double, and the images are sepa-
rated more and more as the pressure is increased, and as it
changes the direction of the axis more and more. On the
other hand, two objects, one placed in front, and the other
beyond the point of convergence of the two axes, but in
the same direction, give but one impression, and we see but
one.

Double or single vision with two eyes is explained by the
correspondence of the terminal divisions of the retina in each
eye. These are called the identical points. When the rays
of light strike corresponding divisions in each eye, the sensa-
tion is single, but when they strike portions which do not
correspond, it is double. This correspondence of the parts
of the retina is shown by pressing lightly with the fingers on
the closed eyes. If the internal or external angle of the eyes
be pressed simultaneously, luminous images will be formed at
the points directly opposite those which are pressed, and if
the pressure be applied to the internal angle of one eye and
the external angle of the other, or if we press the upper por-
tion of one and the lower portion of the other, we see but a
single image. From this we conclude that in the first ex-
periment the two points pressed upon do not coincide because
we see two distinct images, and that in the second they do
correspond because we see but one. According to Miiller,
if we consider the retina as a sphere, the pole of which is the
middle of the membrane or at some point in the same direc-
tion and at the same distance from the middle, the corres-
ponding or identical points, on a section of this sphere,
occupy the same meridian and the same parallel. Thus, in
seeing with two eyes, the two images cause but a single
sensation when they are formed on the corresponding por-
tions of the retina, and consequently we receive a double
sensation when they are placed on divisions which are not
identical.

Stereoscope. — From what has been already stated it would

172 THE HUMAN BODY.

seem that in order to give but a single impression, the images
perceived by both eyes should be exactly alike. But experi-
ment demonstrates that two images differing in some respects,
do notwithstanding give but a single sensation to the brain.
When we look at a solid like the pedestal of a column or a
monument, a moment's attention shows us that the outlines
corresponding to the right of the spectator give a larger image
to the right eye than to the left, and that each image differs
from the other; the combination of the two sensations gives
us the idea of relief.

If now we obtain by photography, or if we trace by a single
white line on a black ground, the projection of this monument
or pedestal, in conditions identical with those under which
our eyes receive a double impression, the two images placed
in the direction of the optical axes, as the surfaces would be
which they represent, will give us the impression of the solid
in question by a single image. We owe to Mr. Wheatstone
the demonstration of this phenomenon, and the invention of
an instrument which renders the proof very easy and simple.
This is the stereoscope, the application of which is so widely
known.

When the eyes are first applied to the instrument, in pro-
portion as the optic axes converge, the two images are seen
one over the other, and when at last we perceive but one,
instead of a plane surface we have a relief under our eyes,
which, in certain cases, produces a complete illusion. But
as M. Longet observes, the unity of the image does not
prove that there is but a single sensation, and the two dif-
ferent images do not give birth to a simple sensation, but are
the source of one complex though indefinable one, that of
solidity. How this blending of two different impressions is
effected, is one of the mysteries of our organization ; but the
sensation of relief evidently arises from a combination of
conditions different from those which determine single vision
by means of two eyes.

When vision embraces a certain extent of space, as a land-
scape or a gallery of pictures for instance, the objects appear
single to us, although for the most part they are out of the
direction of the optical axes, but on observing closely we find

ALTERNATION IN ACTION OF THE EYES. 173

that we never fix the eyes except on a very limited portion
of the space spread out before us; the objects thus normally
seen occupy our whole attention, and turn it away from the
other images of which the vagueness or duplication passes
unperceived. When we endeavour to determine these facts
we find that the boundary lines of the objects and the borders
of the pictures appear double, but dim and confused, when
outside of the point of convergence of the ocular axes.

Alternation in the action of the eyes. — When we look at two
circles in the stereoscope, alike in size but of different colours,
or if they are traced on white paper, and contain two different
letters, we distinguish alternately one image and then the
other, and when after a longer or shorter time we succeed in
seeing them superposed, very soon they again alternate. The
two eyes do not act simultaneously in experiments of this
nature, and it is sometimes the impression produced on the
right eye, and sometimes that of the left, alone which reaches
the brain. This periodicity is especially regular in persons
whose sight has the same range in both eyes. And we
remark also that the distinct image is covered with spots of
the same colour as that which is invisible.

This last phenomenon seems to indicate that the retina is
not equally sensitive throughout its whole extent. The alter-
native preponderance of one eye over the other in vision is
due to causes not thoroughly known, though it may be
attributed, partially at least, to the fact that the eyes are
• . unequal in extent of vision, or rather in skill in seeing. We
ostly all of us use one eye more than the other in ordinary
vision, and especially when we look attentively at an object.
It is with the eyes nearly the same as with the hands in this
respect, one is exercised more than the other, and it is
generally the right eye. We have seen that the difference
between the two eyes may amount to myopia in one while
the other is perfectly normal. This inequality, even if slight,
must tend to a difference in the power of accommodation
and to discord in action which constantly inclines to cease
and then to again reproduce itself.

As for the inequality in sensibility of the different portions
of the retina outside of the blind point (punctum ccecum) the

174 THE HUMAN BODY.

displacement of the spots proves that it is not permanent.
We know also that this partial insensibility may be induced
by a brilliant light, and particularly by the rays of the sun.
It is an experiment we all make involuntarily, and which will
be discussed in another place.

Persistence of retinal impressions. — The impressions made
by the luminous rays remain for a certain time, and are then
gradually effaced; it is plain then, that if the action is repro-
duced at shorter intervals than the duration of the impres-
sions, the brain perceives, not a series of sensations, but a
continuous one. Thus in the rapid rotary movement of a
burning coal, the eye perceives only a luminous circle, and
when a wheel revolves rapidly, the spokes seem to approach
each other and form a continuous surface. The impression
of colour persists as well as of form ; and if we cause a circle
divided into party-coloured sections to revolve rapidly, they
produce the sensation formed by a blending of them together;
reel and blue, for example, look like violet, and a great
variety of different shades produce an impression as of gray.
According to M. Plateau, the duration of impressions on the
retina is about half a second.

This persistence of impressions has given rise to the con-
struction of an apparatus, which is at the same time an
object of amusement and a curious philosophical instrument.
Such is, for example, the phcnakistiscope. It was upon the
same principle that the beautiful experiments were founded,
by the aid of which Wheatstone measured the duration of
lightning flashes.

Accidental images. — We may compare to a certain extent
the action of light on the retina to that of pressure on an
elastic surface. When the rays of any colour strike the
retina, it resists the impulse of the luminous wave, and
strives to regain a state of repose. When the action of light
abruptly ceases, as when we close the eyes, for example,
after a very short time, which is measured by the duration of
the impression produced, the retina returns to its normal
state by a reaction which is more energetic in proportion to
the length or duration of the action. It passes by a sort of
oscillation from the condition in which it was placed by the

ACCIDENTAL IMAGES. 175

luminous rays, that is to say, from the positive condition of
impression to a negative one, and then forced by the re-
action, it passes the point of repose, and recedes in an
opposite direction. These oscillations continue for a variable
time, growing feebler and feebler. The reaction of the
retina, and the negative phases of impression, give rise to a
new sensation independent of any external agent, by pro-
ducing what are termed accidental or consecutive images.

We know that two colours are complementary to each
other, which when mingled together produce white; but the
accidental images have the peculiarity of presenting them-
selves in the colour complementary to that of the luminous
rays which have excited the retina; thus, if we look steadily
for a certain length of time in a very clear light at a wall
painted red, the accidental image is green, and if the wall is
orange, the image will be blue, &c.

If, on going into a dimly lighted gallery, we fix our eyes
for a minute or two on a window which receives the diffused
light, and then shut them suddenly and cover them so as to
place them in complete darkness, the primitive impression
of the window, with the panes lighted and the sashes dark,
remains for a time, but very soon the consecutive image
appears with the frame luminous and the glass obscure.
This last image will appear sooner if a little light be admitted
through the closed lids; but in all experiments of this kind,
the eyeballs must be kept perfectly still under the veil with
which they are covered, for the slightest change in the direc-
tion of the optic axes will cause the images, whether primi-
tive or accidental, immediately to disappear.

One of the most important facts in this portion of the
history of the eye, we owe to the observation of M. Plateau.
It is that the duration of the uniform intensity of the retinal
impression, up to the moment when it begins to decrease, is
short in proportion to the intensity, that is in proportion as
the light which produced it was brilliant and white ; so the
impression is less and less durable in its first intensity ac-
cording as it is produced by looking at a blue, red, yellow, or
white disk; if, on the contrary, we measure the impression
not only in its period of uniform intensity, but from its

i76

THE HUMAN BODY.

maximum to its minimum, it is long in proportion to the
brilliancy of the light, that is to say, as the disk is white,
yellow, red, or blue.

Several physiologists explain the formation of accidental
images by persistent excitation of the retina with diminution
of sensibility. They think that the light proper of the retina
plays a part in this phenomenon.

Fig. 41. — Irradiation.

Irradiation, accidental fringes of light. — When one portion
of the retina is excited by the luminous rays, the vibration
is extended to the neighbouring portions, and more strongly
in proportion as the light is white ; the result of this is, that
of two objects of equal dimensions but of different colour,
the lighter one in colour appears the larger in size. If
a black circle is traced on a sheet of white paper, and a
white circle of the same size on a sheet of black paper, and
both placed at an equal distance from the eye, the white one
appears larger than the black. In the same way, if we make
a disk half white and half black, the white half appears the
larger. In both cases the white encroaches upon the black,
because the impression made by it upon the retina is more
vivid, and the longer the experiment is continued the greater
appears the difference in diameter. The name of irradiation
has been given to the group of phenomena of this nature.
It is the same cause which produces a ring of complementary
colour around an image impressed on the retina by a coloured
object. If a square of red be placed upon a white ground,

DALTONISM. APPARENT MOTION. 177

and the eyes are fixed upon it for a time, a border of pale
green forms itself round the red ; and in the same way a yellow
square on a white ground produces a blueish crown round
the yellow image: these are called accidental fringes of light.

M. Chevreul has discovered some remarkable laws which
govern the contrast of colours, and the mutual influence
which two colours placed in juxtaposition have upon each
other. The investigations of the eminent professor are not
more important for the arts than for science, for the pheno-
mena of irradiation are produced constantly in vision, and
artists should not forget them for a moment in painting or in
architecture. It is unnecessary to remark that the harmonious
or discordant effect produced by the association of colours in
these two arts is of the utmost importance, and although in
general the spectator troubles himself very little about the
law of contrasts, yet he is notwithstanding very sensible of
the impressions which result from its observance.

Daltonism — The effects of a disturbance in vision described
for the first time by an English chemist who was attacked
by it, are commonly designated by this term. It consists of
a difficulty, more or less great, of distinguishing colours, some
of which are entirely confounded although very different, as
rose and gray, red and green, &c. Very marked cases of
Daltonism are rarely met with, but in a slight degree the
affection is not uncommon.

Apparent motion of objects. — Among the most common
optical illusions we may cite those which consist of the
apparent motion of external objects. When on a boat, for
example, or in a carriage which is in motion, we seem to be
at rest while the shore or the sides of the road seem to be in
motion. We have no consciousness of the movement of
external objects except by being ourselves at rest, and when
the image of an object moves across the retina while the eye
and the body are in repose, the object seems to change its
position relative to us. Carried along by the boat or carriage,
without our bodies taking any active part in the movement,
we judge of the relative displacement instinctively, and from
habit we refer to external objects the movements which we
d-^ not ourselves feel.

12

178 THE HUMAN BODY.

Sometimes there is an apparent displacement of objects,
although neither the objects nor the eyes are in motion, but
in a normal condition it is always after a movement of the
body that this phenomenon appears. As when the body is
whirled round rapidly and then suddenly stopped, every-
thing seems to turn in an inverse direction. It is probable
that the illusion then depends on the impulse to movement
in a certain direction imparted to the brain; in fact, if we
stop after turning round, the sensation of turning persists for
some moments, especially in the head; and if we refer it
instinctively to external objects, it is in consequence both of
the persistence of the previous sensation, and of the idea of
our actual immobility. We turn still, just as after having
laid down a burden we continue to feel its weight upon us.

Gratiolet ascribes the apparent motion of objects under
these circumstances to insensible oscillations, which displace
to a limited extent the ocular axes, but he does not indicate
the cause of these oscillations.

Optic nerve. — The visual impressions are transmitted from
the retina to the brain by means of the optic nerve, of which
that membrane appears to be the expansion. The two optic
nerves converge from the base of the orbit toward the centre
of the base of the skull, where there is an interlacement of
their fibres in such a manner, that a portion of the right
nerve goes to the left side of the brain, and a part of the left
nerve to the right side; this is called the chiasma, or commis-
sure of the optic nerves. Physiological theories, which are
no longer tenable, have been deduced from this crossing of
the nerves, and nothing positive is yet known of the relation
between this disposition and the visual function. Mechani-
cal irritation of the nerve seems to develop luminous impres-
sions as in the retina, but it causes no pain whatever.

Movements of the eye. — The ocular globe is put in motion
in the orbit by six muscles, grouped two by two, which raise
or lower the eye, turn it inward or outward, or on its antero-
posterior axis. In these movements the centre of the
globe is immovable, and the eye moves around its transverse
and vertical diameters. These, three orders of movements
are independent of each other, and may be made singly, or in

MOVEMENTS OF EYE. RANGE OF VISION. 179

combination, in such a manner as to direct the pupil towards
all points of the circumference of the orbit. The straight, supe-
rior, inferior, external, and internal muscles move it upward,
downward, inward, and outward, and their successive action
gives it a movement of circumduction. The two oblique
muscles turn the eye on its antero-posterior axis, in such a
manner as always to maintain the horizontal position of its
transverse diameter, when the head or the body inclines to
the right or the left. All these muscles take a direct or indi-
rect part in every movement of the eye; if looking up or down,
for example, the straight, superior, or inferior acts alone ; the
other muscles assure the movement, and confine it to the
transverse axis. Such is the perfection of this mechanism,
that the cornea is raised or lowered without the least lateral
deviation, like the objective of a meridian glass; and the eye
perceives by this succession of movements if the image of a
line on the retina deviates o '00002 of an inch from the
vertical.

The eyelids follow the movements of the globe when it is
raised or lowered, obeying the action of the muscles of which
they receive the aponeurotic prolongations.

The movements of the two eyes are always symmetrical,
and of the same kind; both are raised or lowered at once,
directed to right or left, or around their axes; they can be
turned inwards simultaneously to see an object very near at
hand, or slightly outwards, when they turn from such a point
to one in the distance. Even when one eye is closed, the
globe turns in the same direction as that of the open eye.
This unity and variety of movement contribute to make the
eye the most important feature of the physiognomy.

Extent and delicacy ' of vision. — As regards the distance at
which man can distinguish objects, he is less gifted than
many other animals; but in every other respect his visual
powers are at least equal to that of inferior beings. We know
very little of the sensations produced in animals by colours;
it seems probable that they have a relative perception of
them to a certain extent, as the sight of red irritates the bull,
for example; and we know that birds of prey from a great
height in the air distinguish the colour as well as the form of

I So THE HUMAN BODY.

a lark or a quail hiding in the ploughed fields, although it so
closely resembles that of the soil. But if we should suppose
them endowed with sensitive faculties, useless within the
limits of their instinct, could we find anything in animals
more perfect than the organs to which man owes the prodi-
gies of painting? We must, however, distinguish here between
that which pertains to the visual apparatus, and that which
proceeds from the intellect. The eye perceives the tints
which nature offers in almost infinite variety; the mind com-
pares them, and recognizes the elementary colours of which
they are composed; the eye reflects in turn the model, the
palette, and the picture; the mind perceives the relation of
shades, and combines them in such a manner, that by
mingling or contrasting them such a result is produced as
conforms to the first impression; but in order that an artist
may judge whether red or blue predominates in a violet tint,
in order to appreciate the shade, the retina must transmit it
to the brain in its purity.

At the manufactory of the Gobelins, we see the wools used
in the fabrication of the tapestries arranged according to their
shades. The number of these shades exceeds 28,000, and
yet when we compare two approximate shades we distinguish
them with facility, and perceive the interval which separates
them.

The people who live in the country, seamen, and especially
men living in a savage state, generally have sharper sight
than the residents of cities. May not the habit of seeking to
distinguish objects at a distance give the eyes a power which
is not acquired when they always act within a limited hori-
zon? Without assimilating exactly the effects of exercise on
the eye to those which result from exercise of a muscle, we
are justified in thinking that an almost incessant accommo-
dation to great distances must influence the eye in that
respect, and if, as is very probable, the accommodation takes
place by the contraction of muscular fibres, the explanation
of the increased range of the eye from exercise is very simple;
but facts are wanting which verify and measure this increase
in individuals. There is no doubt, however, that men from
whom the horizon is habitually distant distinguish certain

RANGE OF SIGHT. l8l

objects at a point where they are confused to other persons,
although within the reach of their vision.

A ship appears on the horizon, a man unacquainted with
the sea can hardly distinguish the sails of this white cloud
springing from the waters; but a sailor will tell you that is a
brig or a three-master, a war vessel or a merchant ship, and
often he will even come at its tonnage, its lading, its nation-
ality, and its name. The Arab and the European in the
midst of the sands of Sahara see on the horizon an object,
which to the European is only a black point without appre-
ciable form ; the Arab sees a camel distinctly, and declares
that it is at such or such a distance, without ever being de-
ceived.

The inexperienced mountain traveller sees before him a
chaos of slopes and abrupt walls, of elevations and windings,
among whicn he can distinguish neither route nor practicable
passage; but the mountaineer sees at once the accessible
points, and the turns which he must take to reach the summit
of the apparently impassable barrier. This proves not that
the sailor, the mountaineer, or the Arab have sharper sight
than the stranger to their country; but that they have learned
to know the signification of such and such details of form,
such a particularity of colour and the like, which are for them
distinguishing marks, which seem to trace before their eyes
the description which they give to their fellow-voyager of
objects that are either confused or imperceptible to him. It
is therefore to acquired notions, and skill in seeing objects,
rather than to extent of vision, that they owe the faculty of
distinguishing objects at great distances.

We find also in all countries, and in all climates, men who
have extraordinary powers of vision. Wrangel speaks in his
voyage to the Polar seas, of a Yakoute who related having
seen a great star swallow little ones, and then vomit them up
again. That man, says Wrangel, had seen the eclipses of
the satellites of Jupiter. Humboldt tells, in his Cosmos, of a
tailor in Breslau, named Schcen, who also had seen the
satellites of Jupiter with the naked eye. No examples of a
greater range of vision are known.

CHAPTER XII.

Sense oj hearing. — Organ of hearing.— External ear; pavilion of the
ear, auditory canal. — Middle ear; tympanum, drum, or membrana
tympani, fenestra ovalis, fenestra rotunda, Enstachian tube, the small
bones of the ear, muscles and movements of the small bones. — Internal
ear; labyrinth, vestibule, semicircular canals, cochlea, membranous
labyrinth. — Auditory nerve. — Noises and sounds; duration, pitch, in-
tensity and quality of sound; passage of sound through air, water, solid
bodies; gravity, sharpness of sound. — Mechanism of hearing ; functions
of different parts of the ear; movement of sounds in the ear; propagation
of sounds to the audilory apparatus by the vibrations of the bones of the
skull. — Opinions of physiologists on the functions of different portions of
the labyrinth; theory of llelmholtz. — Fineness and delicacy of hearing. —
Correctness of the ear. — Estimation of the intensity, the distance, and
the direction of sounds; ventriloquism. — Duration of auditory impres-
sions.— Sensations having an internal origin. — Parallel between the
eye and ear.

The ear. — The organ of hearing is not placed on the face,
like those of sight, smell, and taste; but in the thickness of
the base of the skull. But we may say it belongs to the face
as one of the elements of the physiognomy, by its external
apparatus, which contributes to the expression of the head.
The ear is divided anatomically into three regions — the exter-
nal, middle, and internal ear.

External ear. — This is the least complicated portion of the
organ; it is composed of the pavilion, or projecting part, and
the auditory canal.

T}\e pavilion of the ear is similar, as the name implies, to
the open portion of wind-instruments or a speaking-trumpet.
It is an acoustic horn, which gathers the sonorous waves, and
conducts them to the intricacies of the auditory apparatus.
It consists of an elastic cartilaginous layer covered with a

EXTERNAL EAR.

delicate skin, and is curiously modelled. Its border, rounded
in its upper portion, and folded back on itself, forms the
rim or helix, and terminates at the lower portion in the lobe.
The concha is in the centre, and is bounded behind by the

Fig. 42. — Section showing the different parts of the ear.

A. Pavilion, or projecting ear.

B. External a^^ditory canal.

C. Meinbrana tympani.
I). Tympanum.

E. Incus, or anvil.

M. Malleus, or hammer.
G. Semicircular canal.
H. Cochlea, or shell.
I. Ettstachian tube.

antihelix, and terminates in the auditory canal. The pro-
jections of the tragus and antitragus, separated by an ellip-
tical slope, protect the orifice of this canal, and a down,
which might be called the lashes of the ear, sifts the air as it
passes into the organ.

The pavilion of the ear is directed forward, projects from
the head, and its lines are in beautiful harmony with the oval
of the face.

184 THE HUMAN BODY.

De Blainville compares the curves and the surface of the
pavilion of the ear to those of the head. According to this
naturalist the curve of the superior portion of the pavilion
corresponds to that of the cranium, and the free border of
the rim describes a curve parallel to that which marks the
temporal fossa. When the head is not prominent .in its
middle region, and the temporal fossae are slightly marked, "•
the rim is absent; it is, on the contrary, broad and prominent
when the arch of the skull overhangs the temporal fossae.
The concha corresponds to the upper jaw, and is propor-
tional to it; and the prominence of the origin of the helix
represents that of the zygomatic arch; and lastly, the profile
of the lobe is like that of the upper jaw. It is remarkable
that this lobe exists only in man, and that man only has also
a prominent and angular chin.

The auditory canal, which represents the tube of the acoustic
trumpet formed by the external ear, is cartilaginous next the
concha, and the remaining part is excavated in the petrous
or stony portion of the temporal bone. This canal is about
one and a fifth inch in length, and its entire disposition is such
that foreign bodies suspended in the air cannot pass with it
to the membrana tympani. It is bent near the concha in
such a manner that the air, in transmitting sound to the middle
ear, does not penetrate in right lines, thus protecting the
sensibility of the membrane.

The middle ear. — The membrana tympani (membrane of
the drum), of which the name indicates the function, is a
membranous partition stretched obliquely across the bottom
of the auditory canal, which it separates from the middle ear
or drum. This membrane is semi-transparent and very thin,
although it is composed of three layers; it vibrates under the
impression of the sonorous waves, and transmits the vibratory
movement to the little bones of the ear. Between the
membrana tympani and the internal ear is the drum or the
tympanum, a cavity hollowed out, like all those of the middle
and internal ear, in the petrous portion of the bone. Among
the details of its form and organization, we remark the
fenestra ovalis, which communicates with the vestibule, and
\\\zfenestra rotunda, which leads to the cochlea. The drum

SMALL BONES OF EAR. INTERNAL EAR. 185

also communicates with the mastoid cells, numerous sinuses
which are found in the mastoid process of the temporal bone,
containing air, and designed to multiply the vibratory surfaces;
and lastly, it unites by a sort of funnel with the Eustachian
tube, a canal about one inch and a third in length, which
opens into the upper portion of the pharynx, and admits the
air into the middle ear.

The ossicles or small bones of the ear. — These are four in
number; they are articulated together, and form a bony
chain which runs from the membrana tympani to the fenestra
ovalis, following a broken line. They have been named the
hammer (malleus), the anvil (incus), the lenticular\)QK<t, and the
stirrup (stapes), from their form or their functions. Special
muscles act upon the malleus and the stapes, which are at
the two extremities of the chain ; the incus and the lenticular
bone serving as media for the propagation of the vibrations.
The motion impressed upon one of these extremities is com-
municated to the other by a sort of see-saw movement of the
little bones, the mechanism of which is pretty nearly repre-
sented by that of a bell. One extremity of the hammer, the
handle, is fitted into the membrane of the tympanum, and
when the muscle of the hammer contracts, the membrane
tightens, a phenomenon which will be discussed further on.
The muscle of the stirrup attaches the flat part of this bone
to the fenestra ovalis, and according to M. Longet prevents
it from being forced in a contrary direction under the influ-
ence of the muscle of the hammer, of which it is the an-
tagonist.

Labyrinth or internal ear. — The internal ear is that por-
tion of the organ of hearing which perceives the impression
of sound, and transmits it directly to the brain. It is hollowed
out in the petrous bone, and is divided naturally into three
distinct compartments, named the vestibule, the semicircular
canals, and the cochlea or snail-shell. These divisions form
together one of the most complex and delicate pieces of me-
chanism in the human body.

The labyrinth is composed of a bony cavity which incloses
a membranous cavity in a portion of its space, and from this
circumstance arises the distinction made by anatomists

1 86 THE HUMAN BODY.

between the osseous and membranous labyrinths. We shall
first consider the osseous labyrinth.

The vestibule is an ovoid cavity placed in the centre of the
internal ear, between the semicircular canals and the cochlea.
It communicates with the drum by the fenestra ovalis, which
is closed by the base of the stapes. In it are seen the open-
ings of the five semicircular canals, of the vestibular stair of
the cochlea, and of the vestibular canal. This latter is the
opening of a vascular canal which traverses the petrous bone.

Semicircular canals. — This is the name given to three
curved tubes forming axes of circles, one which is horizontal
and is placed between the two others, which are vertical.
They are each enlarged into a bulbous cavity (ampulla) at
one extremity, and communicate with the vestibule by five
orifices.

Cochlea (or snail-shell). — This is the name given to a
conoid cavity which is separated from the semicircular
canals by the vestibule, with which it communicates, and
terminates at the fenestra rotunda. The cavity of the cochlea
is a spiral, describing two turns and a half round its columella
or axis; it is divided transversely into two portions by a
partition — -the lamina spiralis, throughout its entire length.
That portion opening into the vestibule is called the scala
vestibuli; and that opening into the fenestra rotunda the
scala tympani — by which it would, if it were not for the
membrane which closes it, communicate with the cavity of
the tympanum.

The lamina spiralis is divided lengthwise into a bony por-
tion, which corresponds at its internal border to the axis;
and a membranous portion, which attaches the osseous por-
tion to the external wall of the cochlea. This wall is formed
by the spiral plate. The cochlea is lined by a fibro-mucous
membrane, which appears to be a continuation of the perios-
teum of the other two cavities of the labyrinth; the mem-
branous portion of the spiral plate may be considered as a
prolongation of the membranous labyrinth. Lastly, the
vascular canal, called the canal of the cochlea, analogous to
that of the vestibule, communicates also with the cavity of
the skull. The base of the cochlea rests on the bottom of

MEMBRANOUS LABYRINTH. AUDITORY NERVE. 187

the internal auditory canal, by which the auditory nerve
enters the organ of hearing.

Mffttbranous labyrinth. — -The bony walls of the vestibule
and of the semicircular canals inclose and protect a mem-
branous apparatus of the same form, which is separated from
them by a space filled with a limpid fluid vd\\z& perilymp/i or
liquor Cotunnii. The membranous labyrinth is therefore
smaller in proportion than the osseous ; the difference in size
is about one-half. Its cavities contain a fluid analogous to
the perilymph, and which De Blainville has compared to the
vitreous humor of the eye; they also contain semi-transparent
tubes and membranous sacs, the appearance of which is
closely analogous to that of the retina. The membranous
vestibule is composed of two distinct parts, the saccule and
utricle, in which there exists a calcareous dust, which appears
to represent in man and the mammifera the auditory stones
or otoliths of fishes.

Auditory nerve. — The auditory or acoustic nerve specially
belongs to the organ of hearing, and is remarkable for the
softness of its texture: it enters the ear by the internal
auditory canal, and divides into two branches, one of which
distributes itself to the vestibule and to the ampullar extremi-
ties of the semi-circular canals; the other goes to the cochlea,
and has been called the cochlear branch. Its ramifications
are extremely minute; they line the surface of the modiolus
and spread themselves regularly over the spiral plate, dimin-
ishing in length from the base to the summit in such a manner
that if we suppose the spiral plate to be placed upright, and
forming a triangular plane, these filaments would resemble
the strings of a harp — the longest at the base of the triangle
and the shortest at the summit. They are called the fibres of
Corti, from the anatomist who first described them. The
microscope enables us to count more than three thousand,
and we shall see later the part they are supposed to fill in
audition.

But before opening the physiological question, we will
notice summarily some of the phenomena, the existence of
which is revealed to us by the ear.

Noises arid sounds. — Physicists divide sounds into two

1 88 THE HUMAN BODY.

classes — musical sound and noise. They both have the same
origin, the vibrations of a body transmitted to the air. The
short duration of a noise, and the lack of isochronism in its
vibrations, do not permit us to appreciate its musical value,
and this distinguishes it from musical sound. Thus the ex-
plosion of gas or powder, the crack of a whip, or the
breaking of a branch make a noise, but give no musical
sound. The limit between sound and noise is otherwise in-
sensible, and varies according to the individual. A noise as
well as a sound may be grave or acute, feeble or intense.
The difference in the duration of the sensation does not
permit us to compare noise to sound, but yet the ear seizes
the relation between two noises as well as between two
musical sounds.

A sound is called musical when its pitch can be estimated
absolutely and relatively to other sounds grave or acute; or,
in other words, when the number of vibrations follows a
constant law and can be determined.

Whatever may be the difference, however, between a noise
and a musical sound, the one is only a variety or degree of
the other, and both, proceeding from the same source, may
be studied under the generic denomination of sound.

Sound has four fundamental properties — duration, pitch,
intensity, and timbre or distinctive quality. The three first
named are defined by the words which express them: as
for the timbre, it is the resonance peculiar to each instru-
ment, to each voice, which enables us to distinguish without
difficulty the notes of a violin, a clarionette, or a flute, and
to recognize individuals by hearing them speak or sing.

The duration of a sound is measured by the time that the
body vibrates from which it proceeds ; it is high and acute
according to the number of vibrations, and its intensity is
measured by the amplitude or range of the vibrations which
cause it, and this amplitude is in proportion to the force
acting on the sonorous body.

The "timbre" of sounds was long an insoluble enigma to
the physicist. and the physiologist. |. Miiller had suspected
its origin in attributing it either to the isochronism of
sonorous waves of different velocity, or to waves' of different

TIMBRE. SPEED OF SOUND. 189

length, producing a compound wave of a peculiar form,
or else to a longitudinal vibration in the sonorous body
taking place at the same time as the transverse vibration.
M. Longet states, with greater precision, that the timbre
of the human voice, and of wind-instruments, results from
the co -existence of several sonorous waves of different
tone and intensity, which modify the general form of the
principal wave. But at last the beautiful experiments of
M. Helmholtz have demonstrated, that the timbre of a sound
depends upon the number of the harmonic notes which are
produced at the same time as the fundamental note, and
upon their relative intensity.

When a cord of a piano giving the C, for example, is
struck, that note is heard, but a little attention enables the
ear to hear other simultaneous and weaker sounds; they are
the result of partial vibrations which take place in the length
of the cord, according to certain laws which cannot be ex-
plained here. The C given by the shock impressed on
the cord is the fundamental note, the other notes which are
superposed upon it are the harmonics. From their fusion
with the fundamental note, there results to the ear a complex
sound which it decomposes instinctively into simple sounds,
but they cause only a single sensation in the brain, that of
a C having a special timbre. Whether the fundamental
note be given by an instrument or by the human voice,
the same phenomena are produced, and the timbre proves
equally characteristic to the ear. The timbre is therefore
the distinctive quality of the sonorous body — the form, in a
certain sense, of sounds.

Sound moves more rapidly in warm air than in cold; its
velocity in the atmosphere is 1 1 18*45 ^ee^ m a second at 16° C.
(60 '8° F.) or 1 086 '3 7 feet at zero, according to experiments
made by the Bureau of Longitudes in 1822; and according
to those of Bravais and Martins made in 1844, it is 1092*89
feet at zero (Cent.) This velocity is not modified by the varia-
tions in the pressure of the atmosphere, and it is the same
whether in a horizontal, vertical, or oblique direction. It is
increased or diminished by the wind, according as it blows
in the direction of the sound or contrary to it, though the

190 THE HUMAN BODY.

velocity is not changed if the wind blows perpendicularly to
this direction. Sound cannot be produced in a vacuum, and
it is therefore less intense in proportion as the air is more
rarefied. It is weaker, for instance, on the tops of high
mountains than in the lower strata of the atmosphere,
although the profound silence which reigns at times in these
elevated regions permits even very feeble sounds to be
heard at great distances. We were enabled to prove this
with M. Martins in 1844. Near St. Cheron (Seine-et-Oise),
at an elevation of 459 feet, a diapason placed on a drum
could be heard in the daytime 277 yards off; while on the
great plateau of Mont Blanc, at a height of 13,123 feet,
the sound of the same instrument could be heard at a
distance of 368 yards. On the top of Mont Blanc, we
could hear our guides talk at a distance of 437 yards, and
they could hear us speak also.

Humboldt observes that sound is more intense and is
propagated farther in the night than in the daytime, in spite
of the noises and of the wind which in tropical countries
increase after sunset. This diminution in sounds during the
day is attributed by the illustrious observer to the unequal
temperature of the strata of the atmosphere, under the influ-
ence of the sun and the radiation from the earth.

Sound moves much more quickly in water and in solid
bodies than in the air. Colladon and Sturm found its
velocity to be 4708 feet in a second in the waters of the
Lake of Geneva at 8° C. (46*4° F.) of temperature; according
to the experiments of Biot, its average velocity is 10,663 ^eet
in cast-iron pipes. This is about five times greater in water
than in air, and nine times greater in the pipe.

Humboldt records that sometimes volcanic detonations
have been transmitted through the earth a distance of 500 to
745 miles.

It is stated that the gravest sound which can be perceived
by the ear is 32 vibrations in a second (16 according to
Savart), and the most acute, according to Despretz, is 73,700
vibrations. A sound of 60,000 vibrations is, according to
M. Martins, very feeble, difficult to hear, and of such sharp-
ness as to cause a painful impression on the ear. The

MECHANISM OF HEARING. IQI

sounds which are easily perceived and appreciated by the
ear vary from 100 to 2000 vibrations. The gravest C of
a piano of six octaves and a half counts 128, and the most
acute 8192.

Mechanism of hearing. — The sonorous waves penetrate
directly into the auditory canal, or after they have en-
countered the outer portion of the ear, the sinuosities of
which they follow, and the ear itself vibrates to the shock of
sounds, and these vibrations are transmitted gradually to the
organ. Savart, who has demonstrated this phenomenon by
experiments, observes that the very irregular surface of the
ear always presents some portion at an angle most favourable
to the sonorous waves, whatever may be their direction ; in
fact, the force with which they act upon its walls is in direct
proportion to their approach to the perpendicular.

If, for example, the pavilion of the right ear be covered
with some substance which obliterates all the inequalities
and transforms it into a plane surface, a sound cannot be
heard on that side so well as on the left, when produced at
an equal distance from both ears. It is to be presumed,
also, that the pavilion, which increases all sounds equally,
does not vibrate in unison with any one sound, nor has it,
owing to the irregularities of its surface, any one peculiar to
itself. And finally, the form of the pavilion, and its inclina-
tion in relation to the head, seem to have a certain influence
on the acuteness of hearing.

Besides the vibrations which enter directly into the audi-
tory canal, and those which come from the pavilion, this
canal receives also those of the bones of the cranium and
transmits them to the tympanum. These last and those of
the pavilion reach the tympanum sooner than the first, for
the reason already stated, that sounds move more rapidly in
fluids and solids than in the atmosphere. It receives there-
fore two orders of vibrations, but in passing to this membrane
the vibrations of the air are transformed into those of a solid
body; from which we may conclude with Savart and Miiller,
that the function of the tympanum is to serve as a medium
between the air and the small bones of the ear, by changing,
as we have just seen, the atmospheric vibrations.

192 THE HUMAN BODY.

Sounds, augmented by the external ear, and concentrated
upon the tympanum, are transmitted to the little bones,
and again augmented during this transit, by a more close
concentration upon the base of the stapes.

We have seen that the contraction of the muscle of the
hammer causes tension of the tympanum. This membrane
then passes from a state of repose to a variable degree of
tension, upon the effects of which physiologists are not
agreed. According to Bichat, it is more tense in proportion
to the feebleness of the sounds, and to the greater necessity
of action of the organ in order to perceive them. Accord-
ing to Miiller and Savart, the tension protects the organ
of hearing against too violent sounds by lessening the con-
ducting power of the tympanum. According to Longet,
the muscle of the malleus has no other function than to
obviate variations in the tension, and especially to prevent
the entire relaxation of the membrane; in a word, it is the
key of the tympanum.

The sonorous waves traverse the chain of little bones, and
are transmitted by it to the fluid in the labyrinth, thus
changing their medium without losing their intensity. If the
little bones were articulated in such a manner as to form a
rigid straight line, instead of an elastic broken one, the dis-
tance between the tympanum and the fenestra ovalis being
susceptible to variation, the result would be that in certain
cases the pressure on the tympanum and on the fenestra
ovalis would be too great, which the elasticity of the chain
and its articulations prevent. The tympanum can only exert
a limited pressure on the fenestra ovalis, and when it is at
its greatest distance from it, the stapes is held in its place, in
front of this opening, by its muscle. This is the theory of
Savart, which was adopted and developed by M. Longet.

The walls of the tympanum inclose air, which propagates
the vibrations from the tympanum, and transmits them by
means of the membrane of the fenestra rotunda to the fluid
of the labyrinth. These vibrations lose their intensity on
becoming aerial, and this fact has led to the idea that possibly
they may differ in their timbre from those transmitted by the
little bones.

HEARING. THE MIDDLE EAR. 193

However this may be, the principal use of the air in the
cavity of the tympanum is not to transmit the vibrations of
that membrane; but to balance the pressure of the atmosphere
on its external surface, and thus to render it completely in-
dependent between two equal pressures. This is effected by
means of the Eustachian tube, which conducts the air into
the middle ear. The temporary obstruction of this canal
induces buzzings in the ear, causing temporary deafness,
which is intensified by its entire obliteration. The canal
also serves as an outlet for mucus and other fluids, which
may be secreted in the cavity of the tympanum.

The sonorous waves enter the vestibule by the fenestra
ovalis; this opening is closed by the base of the stapes, and
receives the vibrations from the chain of little bones. The
membrane of the fenestra rotunda transmits to the scala
tympani of the cochlea the aerial vibrations of the cavity of
the tympanum. This membrane, as Scarpa has remarked, is
a secondary tympanum.

On reaching the labyrinth the vibrations are propagated to
the fluid which bathes it, and thus reach the membranous
labyrinth, and the scala vestibuli of the cochlea, where finally
they encounter the extremities of the ramifications of the
auditory nerve.

Besides the sonorous aerial waves, the ear perceives, as
has already been stated, those which have been caused by
an impression on the bones of the skull. Thus, when a
sonorous body is held between the teeth, or against the walls
of the cranium, the sound is perceived by the auditory
apparatus. It is in this way that, in spite of the loss of the
tympanum and the small bones of the ear, some persons can
still perceive sounds of external origin. But it is indispens-
able that the membranes of the fenestra ovalis and fenestra
rotunda, which close the openings of the labyrinth into the
cavity of the tympanum, should still remain perfect, and that
the fluid of the labyrinth should still bathe its cavities. But,
as may be easily conceived, hearing under these circumstances
is very limited, since it can only take place when the sonor-
ous body is in contact with the bones of the head.

The functions of the three divisions of the labyrinth have

194 THE HUMAN BODY.

been differently stated by different physiologists. According
to Duges, the vestibule concentrates the sound, measures the
intensity, and consequently judges of the distance. It has
been supposed that the semicircular canals either give the
idea of the direction of the sonorous waves, and of the posi-
tion of the body from whence they emanate, or are simply
organs for increasing the sound. De Blainville thinks that
the function of the cochlea is to appreciate very acute sounds,
Duges makes it the musical portion of the auditory organ,
the appreciator of notes, and the special apparatus for the
perception of voices and articulate sounds.

Other authors have thought that the spiral plate (lamina
spiralis), which narrows regularly from the base to the summit
of the cochlea, corresponds to the scale of notes, from the
gravest to the most acute, and that it vibrates in unison
with each one of them.

According to Miiller and Longet, the object of the cochlea
is to furnish a solid plate upon which to spread the nervous
filaments, in contact with the bony walls of the labyrinth and
of the head, as well as with the fluid of the labyrinth; thus
being able to transmit to these filaments the vibrations com-
municated to the solid or fluid portions of the auditory
apparatus. And also, the spiral form of the cochlea gives in
the least possible space a relatively large extent of surface
for the expansion of the nervous filaments.

This diversity of opinion is easily understood, the moment
we pass from natural facts to physiological speculations.

The auditory nerve is distributed to every portion of the
labyrinth; but before entering it, while in the internal auditory
canal, it divides into two branches, the smaller one running
to the cochlea, and the larger to the vestibule and the semi-
circular canals. If we admit that the two branches are homo-
geneous, and only constitute two divisions of the auditory
nerve, we must conclude that the auditory impression is per-
ceived all over the labyrinth, just as the visual impression is
felt on every portion of the retina. The division of the
nerve, and the peculiar disposition of the ramifications in
each of the labyrinthine cavities, seem to indicate a special
function for each of these cavities. It seems natural to sup-

HEARING. THE INTERNAL EAR. 195

pose that apparatus so different in form, and so distinct
in the different parts of the organ, should have a special
object, and that they combine their functions to produce the
complex sensation of hearing. Miiller has demonstrated that
the same aerial vibrations act with much more intensity on
the fluid of the labyrinth, after having traversed the chain of
small bones and the fenestra ovalis, than they do after
traversing the air in the cavity of the tympanum, and the
membrane of the fenestra rotunda ; he thinks that the waves
of the same sound transmitted through the two fenestrse
differ not only in intensity, but also in their timbre up to a
certain point, since those reaching the fenestra rotunda are
aerial vibrations, and those reaching the fenestra ovalis, by
the chain of small bones, are in the state of vibrations of
solid bodies. But the cochlea also receives sonorous waves
of both kinds by the scala tympani and the scala vestibuli;
and farther, the cavities which form the labyrinth communi-
cate with them, all being filled with a common fluid, and
all united by their walls ; they would seem therefore to be
bound together up to a certain point as regards auditory im-
pressions, and nothing demonstrates that vibrations are elec-
tively directed in their movement on leaving the vestibule,
either toward the cochlea or the semicircular canals.

It must be admitted notwithstanding, that authors gener-
ally agree in placing the principal, and indeed only seat of
auditory impressions in the cochlea, and this is the doctrine
now professed by M. Helmholtz, to whom we owe our know-
ledge of the origin and mechanism of the timbre of sounds.
We will briefly state his theory of hearing.

We have already seen that the terminal filaments of the
acoustic nerve spread themselves regularly side by side over
the lamina spiralis of the cochlea, like the cords of a key-
board; the eminent professor of Heidelberg compares these
nervous filaments to the strings of a piano, and explains their
functions in the following manner. If the piano be opened,
and a person sings loudly above the strings any note what-
ever, the sonorous waves cause the strings which respond
to the harmonics of the voice, to vibrate also; each one of
these strings vibrates exclusively in unison with one har-

196 THE HUMAN BODY.

monic, and the note is thus decomposed by their sympathetic
vibration. The same phenomenon takes place in the in-
ternal ear. The fibres of Corti decompose the sounds, each
one vibrating in unison with the harmonic with which it
accords, arid these vibrations transmitted collectively to the
brain by the acoustic nerve give the sensation of the funda-
mental note, and of its timbre. But here, as in every other
instance, the living organ is infinitely superior to the machine
constructed by man. The fibres of Corti number upwards of
three thousand, and this gives four hundred sensitive cords
to each octave, of which the interval or space is one sixty-
sixth of a note. It is easy to understand from this how a
cultivated ear can appreciate the slightest difference in
sounds, as the eye perceives the least difference in the
degrees of light.

This theory explains one of the most mysterious parts of
the mechanism of audition, it shows us the sonorous waves
exciting the Eolian harp of the acoustic nerve, just as direct
observation enables us to see the luminous image painted on
the retina. Just as a mirror and the camera obscura repre-
sent the eye, an instrument of music represents the ear; and
we follow the sonorous and the luminous waves to the point
where all is shrouded in mystery — to sensation, to comprehend
which we must as little pretend, as to penetrate the mystery
of life, or of our own intelligence.

But the ingenious explanation of M. Helmholtz does not
at first seem to make the phenomena of hearing as accessible
as those of seeing have become by means of optical instru-
ments. The convex mirror, and the productions of photo-
graphy, show us magnificent monuments and vast landscapes
reproduced in microscopic proportion; we have nothing like
this for the ear, and we are involuntarily led to contrast the
auditory organ and its fine canals with the grandeur of
sounds, and of the bodies from which they emanate. Phy-
sicists admit that the sonorous waves cross each other in the
air in nearly the same manner as in a fluid, without modify-
ing their curves, and it is thus that the distinctness of each
particular sound is perceived in an accord executed by
several different instruments; but, in order that this pheno-

ACUTENESS AND DELICACY OF HEARING. 197

menon of hearing may be displayed, the sonorous waves
must move through the windings of the labyrinth with the
same facility that they traverse space; the rush of meteors,
and the immeasurable voices which nature has given to the
atmosphere, to the ocean, and to mountains, must be trans-
mitted to our ears in their relative proportions, as well as
the sound of a falling dew-drop. How can the ear in its
infinitesimal proportions perceive with equal precision the
sound of the gigantic instruments which vibrate under the
hand of nature, and the feeblest noise which traverses the
air?

Let us remember that if we get a glimpse of the details
of natural phenomena, and of those movements which con-
stitute life, it is not in considering them as a whole, but in
analyzing them as far as our limited means will permit. In
the vibrations of the globe of air which surrounds our planet,
as in the undulations of the ether which fills the immensity
of space, it is always by molecules which are intangible for us,
put in motion by nature, always by the infinitely little, that
she acts in exciting the organs of sense, and she has modelled
these organs in a proportion which enables them to partake
in the movement which she impresses upon the universe.
She can paint with equal facility on a fraction of a line of
space on the retina, the grandest landscape or the nervelets
of a rose-leaf; the celestial vault on which Sirius is but a
luminous point, or the sparkling dust of a butterfly's wing :
the roar of the tempest, the roll of thunder, the echo of an
avalanche, find equal place in the labyrinth whose almost
imperceptible cavities seem destined to receive only the
most delicate sounds.

Acnteness and delicacy of hearing. — It has been said that
hearing is the most perfect of the senses in man. Considered
as a musical instrument the ear is in fact a most admirable
organ, and which man alone possesses; but here, as in the
eye, we must distinguish between the apparatus of hearing
and what pertains to the domain of the mind. The ear
perceives sounds, but the mind estimates their regularity,
measures their intervals, judges them melodious or the re-
verse, determines their discord or their harmony. If the

198 THE HUMAN BODY.

painter is provided with a faithful mirror, the ear is for the
musician a still more infallible guide; not that it surpasses the
eye in delicacy of mechanism, but that the mathematical divi-
sions of sound, and of their intervals, much more minute
than shades of colour, do not admit of confusion. The eye
perceives a great number of tints at the same time, which
may mingle upon the retina either from their vicinity, or from
the rapid displacement of objects, as we see when the
molecules of two colours are mixed together, and when a
disk of several colours turns on its axis. On the contrary,
however rapid the movement in a piece of music, each note
produces a distinct sound, and when several reach it simulta-
neously they always cause isolated impressions. It is thus
that a musician in the midst of the accords of a large or-
chestra is able to distinguish a false note and the instrument
from which it proceeds.

The acuteness of hearing has more influence upon the
delicacy of auditory impressions, than extent of vision has
upon visual impressions; acute vision is not necessary to the
painter in judging exactly of colours, but the ear of the
musician must have an exquisite sensibility in order that he
may appreciate the truthfulness of notes and their harmonic
relations; but when once this idea is acquired it is ineffaceable,
and enables him to create master-pieces which his ear cannot
hear. Beethoven became deaf at forty, and composed all
those immortal works which for himself were never per-
formed except in his mind.

It is not rare to find persons who distinguish musical
sounds with difficulty and confound them as regards the
notes. For those in whom this Daltonism of the ear is ex-
treme, music has no existence; they hear only a succession
of sounds more or less intense, without harmonious relation
or rhythmical succession. Between this condition and that
delicacy of ear which marks the leader of an orchestra or a
good tuner, the degrees are infinitely varied, and absolute
correctness of ear is as rare, at least, as a perfect perception
of colour, although musical impressions seem to demand
less effort, and to be a more common endowment than the
ability to appreciate painting.

MUSICAL EAR. INTENSITY OF SOUNDS. 199

It is said that a false note disturbs more than false colour-
ing, but this is true only within certain limits. A mediocre
amateur listening to the overture of "Der Freischiitz" at the
Conservatory would be shocked, no doubt, if the horn should,
by one of those accidents which it is impossible always to
avoid, be out of tune; but the same amateur after having
heard this same piece executed by a second-rate orchestra
would be very well satisfied with the concert, and would
take into account neither the false notes which might have
escaped nor the want of regard to time or expression, and if
he does not place the two orchestras on the same level, it
will be from personal feelings. Among the crowds which
visit the galleries of the Louvre every year, how many people
prefer a common and inharmonious picture blazing with
colour to a master-piece of Titian !

A person who sings falsely is said to have "no ear," and
often, in fact, it is to the want of exactness in the ear that
the faults in the voice are due. In this case the evil is* be-
yond remedy, the musician who has an incorrect ear can
never be sure of producing correct sounds. But if the falsity
of the note is due solely to an imperfection in the vocal
organ, a man who cannot sing correctly, can play the violin
or violincello perfectly, because his ear judges correctly of
the sounds which he produces from his instrument.

Intensity, distance, and direction of sounds. — As we have
seen, authors do not agree upon the functions of the different
parts of the auditory apparatus in the perception of the in-
tensity, the distance, and the direction of sound. The per-
ception of the intensity of sound seems to depend more on
the relative perfection of the whole organ than on any one
of its parts. Vibrations are transmitted to every part of the
ear, and even to the whole body, in loud noises and sounds.
Thus thunder, the report of cannon, the grave notes of an
organ or of a double-bass viol, cause a tremor in the whole
body; but it is by the vibratory excitement of the auditory
nerve that we judge of the intensity of sounds, as the optic
nerve enables us to appreciate that of light.

In regard to distance, if it is a sound with which we are
familiar, that of the human voice, for example, we judge of

200 THE HUMAN BODY.

it by the greater or less force of the auditory impression. As
for noises of which we do not know the intensity at a given
distance, as thunder, we estimate it in the same way, but
with less certainty according as it is faint or loud.

It is therefore to reasoning, founded on the sensation, that
we owe the ability to judge of the distance as well as the
intensity of sounds, and it is the same as to their direction.
When we hear a sound more distinctly with one ear than
with the other, we judge that it comes from the side on
which the impression is strongest, and the ability of the
organ to seize slight degrees in the intensity enables us to
tell in what position of the head the sound is most clearly
perceived. We are therefore led to place it in a certain
position in regard to the direction, and by this means we
acquire an idea of it within certain limits. Hence, if the
ears are both in the same situation relative to the sound, as
when it is in front of or behind us for example, we find it
impossible to distinguish in which direction it is without
turning the head.

This uncertainty which we always feel in regard to the
exact distance and direction of sounds enables the ventrilo-
quist to produce what are wrongly supposed to be illusions
of hearing, but which are simply errors of judgment guided
by the imagination. The hollow, feeble voice of the ven-
triloquist seems to come from a great distance, from above
or from a certain depth below us, the sense of the words, the
expression of the voice, the varied tones and mimicry of the
juggler, do the rest.

Duration of auditory impressions. — Savart has demonstrated
that the duration of acoustic impressions is about the tenth
of a second. Thus when the vibrations of a body do not
exceed nine in a second, the ear perceives a series of distinct
impressions, but beyond ten or twelve the sensation becomes
continuous.

Sensations of internal origin. — As the eye may be the seat
of luminous impressions produced by other means than light,
so sounds and noises may be heard, without the ears having
been excited by sonorous waves. Ringing and humming
sensations may be produced in or imparted to them, under

PARALLEL BETWEEN THE EAR AND EYE. 2OI

abnormal conditions into which we shall not inquire; and
of which the mechanism is obscure or unknown. A pro-
longed shock to the auditory nerve by a loud sound or noise
will cause a persistent confused sensation, which is felt by
everyone after a long journey by railway, or after being near
a great waterfall or in a mill for a length of time.

Parallel between the ear and the eye. — The eye and the ear
present many analogies, both in regard to their functions
and their anatomy. The pavilion of the ear has been com-
pared to the eyelids, the auditory canal to the anterior
chamber of the eye, the tympanum to the iris, the cavity of
the tympanum to the posterior chamber, the small bones to
the crystalline, and the liquor Cotunnii to the vitreous body.
These organs differ in their nature, like the exciting agents
which pass through them. Sound and light both originate
in vibrations, but transparency is the essential condition of
the organ through which light passes, while sounds are pro-
pagated through all bodies, solid, fluid, or gaseous.

The sense of light enables man to contemplate the admir-
able spectacle of the universe, but for the eye nature is
mute ; to it motion alone denotes life ; hearing completes
our impressions, everything is animated by it, and man takes
part in the life of the external world, and shares the thoughts
of his fellows. The perfection of these two senses enables
us the better to appreciate the connection between the
functions, and the unity of our organs. The sight speaks
more directly to the intelligence, it enlarges the field of
thought, it gives birth to precise notions of light, of form,
of extent; and it permits the communication of thought by
conventional signs. Hearing is a necessary condition of
articulate language ; without it man lives alone, affection and
confidence lose their most precious forms of expression, and
friendship cannot exist.

Auditory sensations act upon the nervous system with
more force than visual sensations. We are carried away by
rhythm, or it adapts itself to our ideas and our passions;
music plunges us into an ideal world, and holds us by an in-
definable charm; in a word, if sight speaks more especially
to the intellect, hearing addresses itself to the affections.

2O2 THE HUMAN BODY.

Sight is certainly more necessary to man than hearing, but
still the blind are generally gay and communicative, while
the deaf seem inclined to melancholy. As to the relative
influence of these two senses on the development of the
intellect, we know that the education of the deaf is slow but
may be complete, while that of the blind is, on the contrary,
rather rapid, but is almost always very limited; many ideas
cannot be acquired by them, and, as has been remarked by
M. Longet, their minds rarely attain maturity.

CHAPTER XIII.

Sense of smell. Olfactory organs. — Nose; nasal fossa ; turbinated bones,
pituitary membrane. — Olfactory nerve. — Odoriferous principles; their de-
velopment, their action on the nervous system. — Smell, — its seat; dura-
tion of olfactory impressions. — Uses, and acuteness of smell.

Olfactory organs. — The smelling apparatus is situated in
the middle of the "face, between the orbital cavities and the
palatine arch. Placed thus above the organ of taste, which
it resembles in many respects, it forms the entrance to the
respiratory passages, and controls to a certain extent the
purity of the air which enters them. It is composed of the
nose and the nasal fossae.

The nose. — Two thin, flattened bones, slightly curved in
their breadth, form the superior portion of the nose. They
are articulated by their internal border in the median line;
at their external border they are united to the ascending
processes of the upper jaw, and they are attached at the root
of the nose by sutures to the frontal bone. Their inferior
borders are attached to the cartilages which complete the
nasal walls. The arch formed by the nasal bones is sup-
ported by a bony partition, to which is attached a cartila-
ginous plate, which divides the nasal cavity into two symmet-
rical halves, and separates the nostrils. A delicate skin
envelops the nose and covers its little muscles, which are
more important from a physiognomical point of view than
from their organic functions.

Nasal fossa. — This is the name applied to two irregular
cavities which are continuous with the nasal cavities; they
rest against each other on the median line, and are bounded
below by the palatine arch, and above by the cribriform

204 THE HUMAN BODY.

plate (cribrum, a sieve, being perforated with numerous holes)
of the ethmoid bone. They open posteriorly just above the
throat. A partition formed by the perpendicular plate of the
ethmoid, the vomer (a ploughshare), and a cartilage separates
the nasal fossae on the median line ; the prolongation of this
cartilage separates the nasal cavity into two parts, as we have
already seen. On the external walls of the nasal fossae there
are bony folds, which are called upper, middle, and lower
spongy bones, and are separated from each other by corre-
sponding passages. The nasal fossae communicate with
numerous sinuses in the substance of the bones of the face
and skull.

The whole internal surface of the olfactory apparatus is
lined with a mucous membrane called the pituitary mem-
brane, this is the immediate organ of smell. This membrane
dips into the numerous inequalities of the spongy bones and
the passages, thus presenting a larger surface to olfactory
impressions. The olfactory nerve is ramified in the pituitary
membrane. It penetrates the nasal fossae through the cribri-
form plate of the ethmoid, but is distributed over the upper
portion only. In the lower portion of the fossae the pituitary
membrane receives only nervous filaments from the fifth
pair, a circumstance to be noted in reference to the mechan-
ism and seat of smell.

Odours. — The philosopher calculates the velocity and in-
tensity of light, he can analyze it, he knows from what sub-
stance a given colour emanates, and if this substance exists
in the star, the rays of which he is observing; he demon-
strates in the vibrations of bodies the origin of the sonorous
waves, and sees in light as in sound, not particles of matter
traversing space, but a movement excited in the surrounding
media. Some learned men have thought that odours also
result from a vibratory movement transmitted to the ambient
air by the molecules of odoriferous substances, but Fourcroy
demonstrated the origin of odoriferous emanations in the
volatility of the immediate materials of vegetables; and
odours are now generally considered as bodies existing by
themselves, and not as a purely physical result comparable
to sonorous or luminous waves; they are extremely minute

MINUTENESS OF ODORIFEROUS PARTICLES. 205

material particles, volatilized in the atmosphere. But here
matter seems to become intangible. The chemist can ex-
tract from a body the essential oil which gives it its odour,
but he cannot separate the odoriferous principle from the oil
itself, and he can only recognize its presence by the special
impression received by the olfactory nerve.

Nothing gives us a more exact idea of the divisibility of
matter than the diffusion of odours. Three-quarters of a grain
of musk placed in a room cause a very powerful smell for a
considerable length of time without any sensible diminution
in weight, and the box in which musk has been placed
retains the perfume for an almost indefinite period. Haller
relates that some papers which had been perfumed by a
grain of ambergris, were still very odoriferous after a lapse
of forty years.

Odours are transported by the air to a considerable dis-
tance. A dog recognizes his master's approach by smell
even when he is far away; and we are assured by navigators
that the winds bring the delicious odours of the balmy forests
of Ceylon to a distance of ten leagues from the coast.

Simple experiments prove that odoriferous bodies emit a
stream of particles so small as to seem to be immaterial.
When a morsel of camphor or a small body saturated with
ether, or minute portions of benzoic acid, are thrown upon
water, they are animated by a peculiar movement, which is
due to the propulsion produced by the invisible vapour
which emanates from these substances.

Heat, light, and other influences modify the production of
odours, and their transmission in space. Certain plants are
odoriferous only at night, and it is especially in the morning
and evening, when the dew is scanty, that flower-gardens
perfume the atmosphere. Rain destroys the perfume of
flowers, probably by its mechanical action, and by lowering
their temperature. It is remarkable also that animal or
vegetable odours are feebler, as the countries are colder in
which the plants or animals live from which they emanate.
Hence perfumes come principally from tropical countries.

It has been stated that substances absorb and retain odours
according to their colour, Thus, the experiments of Stark

206 THE HUMAN BODY.

tend to prove that black garments are more quickly impreg-
nated with an odour, and retain it longer, than light-coloured
garments. On the other hand, A. Dumeril assures us he has
ascertained that white stuffs absorb odours as quickly as
others, but that the odoriferous particles are sooner evapor-
ated from them. There must consequently be in this respect
a difference in odours like that in luminous rays, but the first
of these phenomena has not been at all so clearly demon-
strated as the latter.

Under the influence of a shock, or from friction, certain
vegetable and mineral bodies emit odours more or less power-
ful. Such are several varieties of wood, especially lilac and
Saint Lucy, the leaves of mint, lemon verbena, and southern-
wood, and certain calcareous or silicious rocks. Other plants,
on the contrary, lose their aroma on being bruised, like the
mignonette, the violet, &c. The contact of water, or of
vapour, also develops odours in argillaceous rocks and
several vegetable substances.

Odours have a very marked effect on the nervous system;
but some persons are far more impressible in this respect
than others. There is no doubt that certain odours may
cause grave disturbance in the nervous system; but the ima-
gination sometimes plays a prominent part in the discomfort
produced by a bouquet of roses or violets; the sight of artifi-
cial flowers is sometimes sufficient to excite persons painfully
who believe them to be natural. People often ascribe to
this influence of odours on the brain, what is really due to the
effects of carbonic acid gas, or of poisonous emanations ab-
sorbed by the lungs; and how many persons there are who
do not believe the open combustion of charcoal is innocuous,
because it does not emit so much smell as coal.

But even after making due allowance for the effects of the
imagination, it is certain that odours act as an excitant on
the brain, which may be dangerous when long continued.
They are especially dreaded by the Roman women. It is
well known that in ancient times the women of Rome in-
dulged in a most immoderate use of baths and perfumes; but
those of our times have nothing in common with them in this
respect; and the words of a lady are quoted, who said on

SMELL. 207

admiring an artificial rose, "It is all the more beautiful that
it has no smell."

We are warned by the proverb not to discuss colours or
tastes, and we may add odours also. Men and nations
differ singularly in this respect. The Laplander and the
Esquimaux find the smell of fish-oil delicious. Wrangel says
his compatriots, the Russians, are very fond of the odour of
pickled cabbage, which forms an important part of their food;
and assafcetida is. it is said, used as a condiment in Persia,
and, in spite of its name, there are persons who do not find
its odour disagreeable any more than that of valerian.

Smell. — The air which enters the organ of smell deposits
on the surface of the pituitary membrane the odoriferous
principles with which it is charged, it becomes impregnated
with them, arid it is in its tissues that these principles come
in contact with the terminal fibres of the olfactory nerve.
We have already stated that this nerve is only distributed
over the upper portion of the nasal fossae; in order to produce
the sensation of odours, therefore, the air inspired must reach
not only the inferior but also the superior parts of these
cavities. The nose is contracted at the root like a funnel,
and tends to guide the odoriferous effluvia towards the point
where the impression is to be perceived; and the stronger
the inspiration the higher up the column of air is carried, and
the more it excites the filaments of the special nerve. Some
physiologists have thought, with Magendie, that the nerves of
the fifth pair, which ramify over the lower portion of the
pituitary membrane, were designed to serve the purpose of
smell; it seems to be clearly demonstrated that the sensa-
tions caused by acid or ammoniacal vapours are not olfactory,
but simply painful.

The pituitary membrane in its normal condition is con-
stantly humid, and the secretion with which it is bathed is
one of the indispensable conditions of the function of smell;
and, therefore, we remark at the commencement of a cold in
the head, when this membrane becomes dry, that the sense
of smell is more or less impaired. The nose, by shielding
the membrane from the immediate contact of the air, pre-
serves its functions, and the loss of this organ diminishes,

208 THE HUMAN BODY.

or even completely destroys, the sense of smell. Smelling
is ordinarily involuntary, but it may be rendered more
active by the exertion of the will. The inspirations are
then stronger and more frequent, in order that the odour
which we wish to perceive or enjoy may be carried in greater
quantity toward the nasal arch. But if, on the contrary, we
wish to avoid a disagreeable odour, a sudden expiration takes
place from the nose, and we breathe instinctively through
the mouth, and the soft palate closes the olfactory cavities
behind. It is in this way that we are able to diminish the
disagreeable impression arising from the odour in drinking
sulphureous waters.

Whether odours reach the seat of smell by the nose, or
through the posterior opening of the nasal fossae, the result
is the same; it is by this means that we perceive the aroma
of the food when eating with the mouth shut; but under
these latter conditions the persistence of the impressions
very soon blunts the sensibility. A man fasting immediately
perceives it, if a man with whom he is speaking has taken
the smallest quantity of alcohol, even though it was only a
glass of red wine; after eating we distinguish much less easily
in others the odour of the aliments of which we ourselves
have partaken, and the odoriferous principles of which have
already saturated the olfactory membrane.

The sinuses of the bones of the skull and of the face,
which are in communication with the nasal fossae, take no part
in the perception of odours. It has been thought that they
may contribute by their secretions to moisten the pituitary
membrane, or serve as receptacles for the air, which is after-
ward carried from their cavities to the organ of smell.

Duration of olfactory impressions. — When we have inspired
a strong and penetrating odour, the sensation is prolonged
for a certain time, sometimes for several hours. It is pro-
bable that in this case the impression is not single, but is in-
cessantly renewed by the odoriferous particles with which
the mucus of the pituitary membrane is impregnated, or
which is confined in the air in the sinuses. Sometimes also
the odour has penetrated the garments, or is attached to the
skin or the hair, and from thence continues its impressions.

ACUTENESS OF SMELL. 209

%

Any vigorous exercise, or eating, by exciting the secretions,
generally causes the sensation to disappear, the persistence
of which might be exceedingly inconvenient.

Gerdy makes the sense of smell the counsellor of the
stomach. When the appetite is excited the smell of food is
agreeable; but it is repugnant, on the contrary, when hunger
is appeased, and the sense of smell warns us to take no more
food. We may say, with reason perhaps, that this sense
completes that of taste, by enabling us to appreciate the
aroma, without which food and drink would cause only a
gross sensation, or one at least entirely devoid of all delicacy.
When the sense of smell is lost, or even enfeebled, the taste,
perceiving flavours only, seems almost extinguished, existing -
alone.

The sense of smell is very unequally developed in indivi-
duals, but it is said to be of extreme delicacy in some races
of men, and especially among savages. The stories recounted
of individuals following game by tracking, and of negroes
who could distinguish by smell the tracks of a negro from
those of a white man, seem to indicate a faculty quite as
nearly related to the sense of sight as to the one under con-
sideration; and it must be admitted also that individual ex-
perience and careful attention to particular circumstances
produce the same results when applied to the sense of smell,
as to sight or to hearing.

CHAPTER XIV.

Sense of taste. — Organ of taste. — Special nerves of the organ. — Flavours.
— taste.

Organ of taste. — In describing the mouth as a part of the
digestive apparatus, the functions of its several parts were
explained, as well as of the organs which surround or fill its
cavity. It is only requisite here to repeat that the tongue
receives three nerves, of which one, the great hypoglossal,
gives it motion; and the two others, the lingual and the
glosso-pharyngeal, give it gustatory sensibility. The tongue
participates by its movements in the digestive functions, and
in the articulation of sounds; but it has besides a special
sensibility — it is the principal organ of taste.

Flavours, taste. — The cause and intimate nature of tastes
are no better understood than those of odours. It is by
volatilization that the intangible particles of the odoriferous
principles reach us; it is by a solution more or less complete
that substances impart their flavour, that inherent property
which taste alone reveals to us. We recognize in this way
their acidity or saltness, whether they are sweet or bitter, &c.;
but nothing in the nature of bodies, in their texture, or in
their constituent elements, has ever yet explained their
sapidity. Flavours elude analysis and defy classification,
even that which divides them into agreeable and disagreeable,
for the taste of individuals and of nations singularly differs in
this respect. The Laplander and the Esquimaux drink great
quantities of train-oil, which for them is a greatly esteemed
article of food, and is most admirably adapted to the exigen-
cies of a Polar climate; the Abyssinians eat raw flesh, and
find its flavour excellent, while the inhabitant of the West

FLAVOURS. 211

partakes of it with the greatest repugnance, and only as a
medicine. Oysters, which are so generally esteemed in our
country, are to some persons disagreeable and nauseous;
and truffles, the delight of the gourmand, are rejected by the
uninitiated on account of their flavour and their perfume. It
is the same with almost all alimentary substances ; they are
eagerly sought after by some, and despised or abhorred by
others. Let us remember the proverb, and not dispute in
regard to tastes; each is suited to its own country, and goodly
numbers acclimatize themselves, to the great advantage of
peoples, among whom at first they seem exceedingly strange.
Man should control his taste, and habituate it to all whole-
some aliment; this neither excludes choice, nor blunts the
delicacy of the sense; and while we resist its seductions, we
should give timely heed to its instincts and its counsels, for
they are often invaluable.

Among the substances which we taste, there are few which
address themselves solely to that sense, and not at the same
time to the sense of smell. This mingling together in the
same substance of flavours and odours, and the simultaneous
action of the senses which perceive them, has induced some
authors to consider them as forming but one. They are,
notwithstanding, quite distinct in their seat and in their
function; the mixed sensation resulting from the union of
their impressions differs entirely from that which they cause
singly; we may say that the sense of smell is the necessary
complement of taste, for the latter is reduced to very trifling
importance when it acts alone.

However much flavours may vary, they are all referable to
a very few types, to the mixtures and shades of which we
are quite indifferent when they do not offend us. The taste
solely judges whether a substance is salt or sweet, acid or
astringent, and so forth; but when our food does not awaken
any other sensations, we are tempted, in spite of its flavour, to
pronounce it insipid; vanilla cream and coffee cream, or ices
with rum or with maraschino, do not differ in taste when the
nostrils are closed. If, instead of olive-oil and wine-vinegar,
bleached oil and acetic acid diluted with water be used to
, season a salad, we shall have the sensation of taste without

212 THE HUMAN BODY.

that of smell. We must not then confound with natural
taste that which smell adds to it, and it is to supply the lack
in this respect of what is wanting in our food and in our
blunted senses that we make use of condiments.

We must also distinguish the bodies the action of which
is confined to the sense of touch exercised by the tongue,
and many impressions reputed to be those of taste ought
rather to be considered as purely tactile, such as astringency,
tartness, the irritating or caustic action of certain sub-
stances, &c.

On this principle M. Chevreul has divided substances into
four classes according to the impression which they produce
in the mouth: ist, bodies acting on the sense of touch in the
tongue, such as rock-crystal, ice, and so forth; 2d, bodies
acting on the sense of touch and of smell, such as aromatic
metals, tin and copper for example; 3d, bodies acting upon
feeling and taste, as sugar-candy, common salt, &c. ; 4th,
bodies acting on the touch, taste, and smell, as mint-lozenges,
chocolate, or volatile oils.

All alimentary substances figure necessarily in the latter
class.

Authors do not agree upon the seat of taste; several be-
lieve it extends over nearly the whole surface of the tongue,
to the pillars of the fauces, and to the upper surface of the
soft palate, to the tonsils, and to the pharynx. It is now
generally believed to be located at the tip, at the base, and
on the edges of the tongue, and at a certain limited space
on the anterior surface of the soft palate. According to M.
Longet, the back of the tongue and the pillars of the fauces
are not entirely destitute of gustatory sensibility.

Savoury substances do not produce the same impression
upon all parts of the tongue, many salts on the tip of the
tongue have an acid, salt, sharp, or styptic, at the base a
bitter or metallic taste; others, on the contrary, have the
same flavour on every part. In general, acidity is best per-
ceived at the tip, and on the edges of the tongue, saline or
metallic flavours are developed at the posterior portion.

In order to perceive the flavour, the savoury molecules
must be bathed in saliva, and partially dissolved, so as to be

SEAT OF TASTE. 213

placed in more immediate contact with the surface of the
tongue. . To further insure this contact, the tongue applies
itself to the palatine arch, and presses the food against its
surface. It is then that the gustatory impression is produced
in its full force, and from this it has been inferred that the
palate is the principal seat of taste. The action of the
palate, however, is purely mechanical, and is limited, as we
have stated, to securing immediate contact between the
savoury bodies and the tongue. This is demonstrated by
covering the palatine arch with a thin pellicle which is itself
insipid and impermeable; the taste is just as acute under
- these conditions, but if the tongue is covered with this same
pellicle, and the palate uncovered, no taste is perceived.
The cheeks and lips also contribute to taste by carrying the
particles of food which may have fallen outside the dental
arch during mastication back to the tongue. Taste acts not
less delicately in deglutition, when the contents of the mouth
descend between the base of the tongue and the soft palate
on its way through the throat. Food and drink must re-
main for a certain time in the mouth in order that their full
flavour may be perceived ; thus the gourmand takes care to
retain them, and exhaust, as it were, their aromas, before send-
ing them to the stomach. For this reason, also, wine-tasters
hold the wine in their mouth when they wish to judge of its
quality, but they avoid swallowing this mouthful of wine
after it is thus robbed of its bouquet; they reject it after
thoroughly moistening the surface of the tongue, and they
can then decide as to the vineyard and the year of the
vintage. If they drank the wine which they taste, the smell,
which here plays the principal part, would very soon become
dulled.

The papillae of the tongue, it is generally considered, are
endowed with gustatory sensibility, and this sensibility is
principally attributed to the fungiform papillae. According
to M. Longet they are rather tactile organs, and the learned
physiologist supports his opinion by the fact that, on the
point of the tongue the taste is no less perfect where the
parts are destitute of papillae, while the feeling there is much
less delicate than on the papillae themselves.

214 THE HUMAN BODY.

The impressions of taste are quite persistent according to
some authors, but this persistence is due to the presence of
savoury particles on the tongue, and is more correctly the
constant renewal of the impression. Experience shows how
difficult it is to get rid of certain flavours, and it is easy to
understand that when dissolved, and retained by the saliva
in what may be called the papillary fleece of the tongue, the
particles remain, and furnish for a considerable time the
materials for the sensation. It is a mechanism analogous to
that which produces the persistent smell of creosote and
dextrine from the hands several hours after contact with the
disgusting perfume.

Taste is but slightly developed in infancy, and, although
it acquires some delicacy in youth, it is especially in mature
age that it reaches its perfection. Far from growing feeble
with the lapse of years, it retains all its acuteness, and con-
soles the aged for the irreparable injuries of time. It is per-
fected by exercise, and attains in some individuals remarkable
delicacy, as in professional tasters, for example; but the pro-
longed use of highly seasoned food, the abuse of alcoholic
liquors, and above all of tobacco, enfeebles and blunts it in
what may be termed its olfactory portion.

The question has been raised whether taste is developed
by civilization. This is admitted by several physiologists,
but perhaps it would be necessary to establish a distinction
between the natural sensibility of the organ and its aptitude
in judging of a great number of flavours. In this last respect
there is no doubt of the superiority of civilized nations, but
there is great difference between them notwithstanding, and
if we were to measure the civilization of nations by the deli-
cacy of their taste, we might arrive at very flattering con-
clusions for some, it is true, but at very painful ones for
many others. We will content ourselves with saying that,
in Europe, the taste is generally more developed in the south
than in the north. In conclusion, it furnishes very little
material to the intellect. Its scientific use is limited to in-
dicating to the chemist the sapidity and species of flavour of
substances.

Its functions, in relation to nutrition, dispose to gaiety and

POSITION OF TASTE AMONG THE SENSES. 215

good humour, and nothing except labour produces a more
powerful diversion for the mind of a person a prey to chagrin
or melancholy. Stationed at the entrance to the digestive
passages, it guides us in the choice of food, and controls its
nature and quality; it warns us against repletion by its indif-
ference to the flavours the most appreciated at the beginning
of the repast, and compensates by agreeable sensations for
hunger — the hard necessity of our organization.

Taste is therefore a useful servant, but on the whole we
see that of all our senses, it is not the farthest removed from
matter, and what is worse still, it has much to be pardoned
for. The stomach reproaches it with not being so virtuous
as physiologists seem to believe, and accuses it of being
dangerously seductive, and the worst enemy of those who
should regulate their diet; and though it sometimes gives
timely warning by disgust, it is often in the wrong in reject-
ing wholesome food under the pretext that it is new or that
its prejudices condemn it. The taste retorts by throwing the
blame on those who have taught it to be fastidious; it pro-
fesses, and with truth, to be docile to training, and that the
prejudices come from the master of the house; and it adds
that, though perfectly competent to judge of the merits of a
cook, it is very little acquainted with questions of hygiene,
and that the enemy of the stomach is gluttony and not
taste.

Some persons affect a contempt for this sense, explicable,
no doubt to a certain extent, but which tempts us to be-
lieve that they speak of it only from hearsay. "The mind
should take precedence of the body," as Belisus emphatically
declares; but the good Chrysalus, was he wrong in saying,
"Yes! my body is myself, and I will take care of it?" May
we not remember in proper time and place that "man lives
on good soup, and not on fine words :" besides, one does no
harm to the other, and to want even the most modest sense
is to be imperfect after all. Thenard, speaking of cooking
before a crowded audience at the Sorbonne, called it " that
important part of chemistry."

We may think what we please of the taste, but it has
always in all ages been the endowment of men of genius.

2l6 THE HUMAN BODY.

In reading Brillat-Savarin, we feel disposed to believe that
the mind and the gastronomic senses are inseparable. But
these are delicate questions; and as we would not toss an
apple of discord between nations, neither shall we between
individuals, but rather prudently refer the reader to the
Physiology of Taste.

CHAPTER XV.

Sense of touch — Difference between touch and feeling. — Tactile sensibility
and general sensibility1' — Organ of touch. Sensation of contact ; dif-
ference in the sensibility of different regions of the body ; simple contact,
shock, vibration. — Sensation of pressure; relative aptitude of different
regions in appreciating it ; variable sensation according to the form of
the body and the extent of its surface. — Sensation of temperature, variable
according to the temperature of the skin, the density of bodies, and the
surface in contact : identical sensation from contact with a body very hot
and very cold; relative sensibility of different regions to temperature. —
The touch; its delicacy. — The touch compared with the other senses;
illusions of touch; persistence of tactile impressions, sensations from in-
ternal or subjective causes; causes which modify feeling.

Touch and feeling. — Tactile sensations, like all others, are
more or less complete according as the attention is, or is not,
directed to them. The contact of a foreign body with any
sensitive portion of the organism is revealed to us \)j feeling,
and it is by touch that we discover the form, resistance, and
temperature of this body. Feeling may be involuntary, touch
is an act of the will; there is therefore the same difference
between feeling and touch that there is between seeing and
looking; between hearing and listening, scenting an odour and
smelling it, perceiving a flavour and tasting it.

We must also distinguish between impressions due to
general sensibility and tactile sensations proper; thus, if we
knock the elbow we feel an acute pain along the course of
the ulnar nerve, but the impression produced on the skin is
perfectly distinct from this deeper suffering when not entirely
masked by it. It is the same in sensations resulting from a
shock to the right hypochonder which produces a pain in the
liver. All the tissues which receive nerves of sensation may

2l8 THE HUMAN BODY.

be the seat of impressions which may be referred to the
general sensibility, and which are for the most part painful;
impressions on the sense of touch are only produced in
certain tissues specially endowed with this sense. General
and tactile sensibility are independent of each other, and
they are not developed proportionally; as, for instance, the
palmar surface of the ringers is endowed with an exquisite
sense of feeling, but it is almost insensible to a blow which
would be very painful to the cheek, in which this sense is
much less developed.

Organ of touch. — Touch has its seat in the skin throughout
its whole extent, and in some of the mucous membranes. It
is by the nervous papillae containing the tactile corpuscles
that the impression is perceived, and the tactile sensibility of
any region is in proportion to the number of nervous papillae
existing in it.

We receive three distinct impressions at a time by the
sense of touch — that of contact from a foreign body, that of
the pressure which it exercises on the skin, and that of its
relative temperature.

The sensation of contact is not equally distinct and precise
in all parts of the body, and the reason of this we will
endeavour to explain. If we apply simultaneously the two
points of a compass to the skin, they must be more or less
separated according to the region experimented on, in order
that their contact may cause one or two distinct sensations,
and we may in this way measure the delicacy of the sense at
any given point on the skin. It is evident that the less
sensitive the skin is, the more widely we must separate the
points of the compass to produce a double sensation.
E. Weber after many experiments classes the regions in the
order of their sensibility as follows : — The tip of the tongue
gives a double sensation when the feet of the compass are
separated about half a line ; the palmar surface of the ends
of the fingers, one line; the red surface of the lips and the
surface of the second joint of the fingers, two lines; the end
of the nose and the palm of the hand near the fingers, three
lines; the back and edges of the tongue at about an inch
from the tip, and the skin of the lips, four lines; the palm

RELATIVE ACUTENESS OF SENSE OF TOUCH. 2 19

of the hand, the cheek, and the eyelids, five lines; the
palate, six lines; the prominence of the cheek, and the sole
of the foot near the great toe, seven lines; the back of the
hand near the fingers, eight lines ; the gums, nine lines ; the
lower portion of the forehead, ten lines; the lower part of
the occiput, twelve lines; the back of the hand, fourteen
lines; the throat under the jaw, fifteen lines; the shoulder,
fore-arm, and knee, eighteen lines; the chest over the
sternum, twenty lines ; the loins, the upper part of the back,
and the neck on the line of the spine, twenty-four lines;
the middle of the back, of the neck, of the arm, and of the
thigh, thirty lines. '

Gratiolet found by oft-repeated experiments that the dis-
tances recognized by the pulp of the fingers might be very
much less. By touching two points on the same papillary
ridge on the pulp of the last joint of the middle finger, sepa-
rated only by the orifice of a sudoriferous duct, the two sen-
sations were plainly distinguished at the distance of less than
one quarter of a line.

The experiments of Valentin, on the other hand, prove
that tactile sensibility varies from single to double in cor-
responding regions in different individuals; we can only
accept the measurements of Weber, therefore, as indicating
the relative sensibility. And lastly, we are indebted to M.
Belfield-Lefevre for the experiments which led him to the
following conclusions. The distance between two points of
contact is better appreciated, if these points are placed on a
line transverse to the axis of the body, than when on a line
parallel to it or longitudinal. According to Weber, on the
ends of the fingers, and on the tip of the tongue, the distance
is better appreciated on a longitudinal than on a transverse
line. The distance between two points of contact, distinct
and simultaneous, is greater in proportion to the delicacy of
feeling in the region experimented on; it seems to be greater
also when the contact takes place successively in the two
points, than when it takes place simultaneously, and greater
also if the two contacts are separated by a longer interval of
time. If the two points of contact are separated by the
median line, the distance between them seems greater than

220 THE HUMAN BODY.

if they are placed on the same side of the body. — If two
points are" touched, which are subject to variation from func-
tional displacement, the eyelids. or the lips for example j the
distance is greater than if the two contacts take place on one
eyelid, or one lip.— This sense is also increasingly developed
on the surface of the limbs in proportion to the distance
from the body.

The sensation of contact varies according as it results from
a simple application of a foreign body to the skin, or from a
shock, or a succession of shocks repeated at short intervals,
like that which produces vibration in a body. In the latter
case the region of contact receives a shock in proportion
to the intensity of the vibrations; as when we touch the skin
with a timing instrument while vibrating, or if we grasp a
vibrating metallic body or wooden rod, or close the lips
against the reed of a basoon while it is being blown into, it
produces on the surface in contact an impression, varying
from a painful shock to a simple tickling or pleasurable sen-
sation. It is a sensation of the same nature, though diffused
through the whole body, that we feel from the vibrations im-
pressed on the atmosphere by the explosion of artillery, the
roll of thunder, or the ringing of a great bell. The sense of
touch then gives us an idea of the sonorous waves which
excite the auditory nerve, and furnishes us with the proof,
that the same cause acts differently on the special nerves of
the different senses. In fact, the nervous papillae of touch
transmit a sensation of motion and of shock; the tympanum
perceives neither tickling nor shock, the impression which it
transmits to the auditory nerve is not that of a vibratory
movement, but of the sound which results from it.

The sensation of pressure is distinctly perceived by touch;
but we must distinguish between the pressure of a body
against the skin, and the resistance which this body offers to
a muscular effort tending to displace it. If when the hand
is supported, and a weight placed in it, no effort is made to
raise it, and the muscles remain inactive, we feel a sensation
of pressure, the force of which may be judged of with more
or less exactness; but the moment we endeavour to appre-
ciate the weight the sensation becomes complex, and we

SENSATION OF PRESSURE. 221

have the idea of pressure, and that of the muscular effort
which we oppose to it; and great attention is necessary to
prevent an instinctive contraction of the muscles of the hand
to resist the weight with which it is charged. We must also
take into account habit and the relative strength of the hands;
as the right, which is generally more used than the left;
may be less sensitive to pressure, and appreciate its degree
less exactly.

Those portions of the skin where the touch is most acute,
and where two points of contact are perceptible at slight
distances, are, according to Belfield-Lefevre, those which
estimate most correctly the degree of pressure; as the lips,
the palmar surface of the fingers, the under surface of the
toes, and the skin of the forehead, are better endowed in
this respect than the rest of the body. But neither touch
nor pressure alone can give an exact notion of the weight,
we must support the body on which the experiment is made
by muscular effort: the inequality of the two hands in this
respect is so well known, that we use one and the other
alternately in order to ascertain correctly the weight of the
object. It is estimated that pressure alone will not enable
us to appreciate more than an eighth of difference between
two weights, but by lifting we can appreciate a sixteenth.

The form of bodies also influences the sensation of pres-
sure; when an object with only a small surface is applied to
the skin the pressure seems greater than when it is spread
over a greater extent; and it may even become painful when
supported on a restricted point; thus, the weight which we
carry with ease on the whole breadth of the shoulder, is in-
tolerable when resting only on one of its angles. A truncated
cone laid on the forehead seems heavy or light according as
it rests on its smaller or larger base. Soldiers and travellers
know very well that they cannot with impunity exchange the
broad bands of their knapsacks for narrow straps or cords.
It is unnecessary to remark, that if the weight be distributed
over a large surface, each point of that surface supports but
a fraction of the entire weight; the whole mass, on the con-
trary, presses on a limited space.

Sensation of temperature. — We recognize by contact with a

222 THE HUMAN BODY.

body whether its temperature is the same, or whether it is
higher or lower than the point of skin which touches it; in
other words, touch gives us an idea of the relative tempera-
ture of bodies. But the sensation may change in a few
moments, as the object in contact with the skin rapidly im-
parts or borrows heat; and if it is warmer or colder than the
skin, an equilibrium is soon established when the difference
is inconsiderable. And the same body may produce a sensa-
tion of cold or heat successively without change of tempera-
ture, according as the surface of the skin at the moment of
contact is warm or cold; thus, if we take a bath in water
cooler than the air, the temperature of the air, which seemed
low on entering the bath, appears warm when we come out
a few minutes after. It is for the same reason that we find
the air of a cellar cool in summer, and warm in winter,
although it has not varied.

The sensation is marked in proportion to the conducting
quality of the object in contact with the skin. Air seems
warmer than water at the same temperature, because the air
being a worse conductor of heat takes less from the skin in a
given time. Air in motion, by exciting evaporation, causes
a very sensible loss of heat, as every one knows; and the
atmosphere also, which seems very cold when the wind blows,
grows warmer apparently when the wind ceases, or when we
are sheltered from it.

The contrary effect from that caused by pressure is here
seen; the sensation is marked in proportion to the extent of
surface. The whole hand appreciates the temperature better
than a single finger; and a body of a given temperature,
applied over a large surface, will give a sensation of more
intense heat than a warmer body which touches only a small
portion of skin. We can easily understand that the skin
absorbs in a given time more heat by a surface four inches
square, than by one only one inch square, and the impression
transmitted to the brain in this experiment represents rather
the sum of the heat absorbed from all parts of the surface in
contact, than the temperature of the body with which the
experiment is made.

When we touch a body of a lower temperature, the same

SENSATION OF TEMPERATURE. 223

sensation is produced as when we touch one at a high tem-
perature. Contact with a ball of frozen mercury causes
a burning sensation, the same as that of iron heated to
100° C. (212° R), though we know that mercury freezes at
— 40° C. ( — 40° F. ) Voyagers in the Polar regions are com-
pelled to envelop the metallic portions of their instruments in
non-conducting substances, so as to be able to handle them
with impunity.

The skin and the mucous membranes do not appreciate
differences of temperature with equal nicety in every portion
of their surface, and the regions which are most sensitive to
contact are not those which best indicate the temperature.
The palmar surface of the fingers, the tongue, and the lips,
are less impressionable in this respect than the skin of the
cheeks, eyelids, elbow, and the pituitary membrane. We
may perhaps attribute this relative insensibility in the hand,
and the mucous membrane of the cheeks, to the habit of
contact with warm bodies. The hand becomes rapidly
inured to hold objects hot enough to cause a painful sensa-
tion to persons unaccustomed to it. We see this in chemists,
blacksmiths, and others. The skin need not necessarily be
thickened, although this condition also decreases the sensi-
bility. We often see persons of mature age bear without
pain the contact of food so hot that younger people could
not swallow it. The mucous membranes of the oesophagus
and the stomach are more sensitive in this respect than
that of the mouth ; but when the food is held immovable for
a few seconds between the palate and the tongue, the heat
is absorbed, and the food or drink may be swallowed with
impunity.

It is clear from the preceding remarks that the sense of
touch is an unreliable thermometer; it is sufficient, however,
to guide us in matters relating to health, and in regard to
external objects, especially when we permit its full develop-
ment by touch.

The hand is the principal means of exercising the touch.
The organization of this admirable instrument, its numerous
articulations, the freedom and variety of its movements, the
tactile sensibility which is so fully developed in the palmar

224 THE HUMAN BODY.

surface of the fingers enables us to obtain, by means of it,
ideas of the form and relative situation of objects, of their
motion, their resistance, their weight, their solid or fluid con-
dition, of their temperature, &c. The hand grasps objects,
moves over their surface, follows their outline, measures their
distance and their extent, as far as the length of the lever
of which it forms the extremity will permit. By the aid of
this lever it raises bodies, estimates their weight, their firm-
ness, and their elasticity. In touching them with the ends
of the fingers it perceives the details of their form and their
relative value. We have seen of how great importance deli-
cacy of touch is to the artist, it is no less precious to the
physician, and it renders him service which he asks in vain
of any other sense. It is by the touch that he arrives at a
knowledge of the state of the circulation, the existence of
fluids in the tissues, and their normal or morbid consistence.

By exercise the touch attains extreme delicacy. The
blind learn to read with facility from letters printed in relief,
and to execute certain work with tools. Saunderson, pro-
fessor of mathematics in the university of Cambridge, was
blind from his cradle, but he had attained to such exquisite
perfection of touch, that in a set of medals he could dis-
tinguish the genuine from the counterfeit pieces, though the
latter were so well executed as to deceive a connoisseur
judging by sight. He felt, by the impression of the air on
his face, when he was passing near a tree. It is said that
Jean Gonnelli, a blind sculptor, could model in clay an
exact copy of a statue the outline of which he had studied
by touch, but doubtless we must take this anecdote with
some allowance for exaggeration.

However this may be, the touch has been from the earliest
antiquity an object of the most enthusiastic admiration to
naturalists. It has been considered as the most exact and
the most infallible of the senses, able to control their testimony
and rectify their errors. It has been placed in the front
rank, and held up as a type of which the others are only the
modifications. Buflbn says, "It is by the touch alone that
we acquire complete and accurate knowledge ; it is this sense
which rectifies all the other senses, which might only delude

COMPARISON BETWEEN TOUCH AND OTHER SENSES. 225

us and make us err, if it did not guide our judgment." But
BufTon thought that "the difference between our senses
results only from the more or less external position of the
nerves, and from their greater or less number in the parts
which constitute the organs." The illustrious naturalist did
not recognize the special functions of the sensitive nerves;
the sensations of colours, of odours, of flavours, and of sounds,
were for him only tactile impressions. How could we admit
that feeling could guide us in judging of the colour of objects,
of their taste, their odour, or their sound ! Even while ad-
mitting that we can compare the excitation of the skin by
contact to that of the retina by the luminous waves, it is not
the less impossible to establish the least analogy between
touch and sight, since the retina is insensible to contact, and
as well as the optic nerve, conveys, not a tactile, but a
luminous impression to the brain. As for the other senses,
if air in vibration comes in contact with the tympanum of
the deaf man he perceives no sound, though he is sensible of
contact from foreign bodies on the tympanum ; if odoriferous
or savoury bodies come in contact with the pituitary mem-
brane or with the tongue of a man who has lost the sense of
smell or taste, he perceives neither odours nor flavours, al-
though he is perfectly aware of the presence of a foreign
body in the nose or mouth.

The touch therefore cannot replace the other senses,
though it sometimes corrects their impressions, but it needs
to be constantly controlled and completed in the sensations
which it produces in us. If it enables us to learn form,
it is the eye which tells us of colour, and often perfects or
corrects our notions of distance, extent, and even of form;
as for instance, we distinguish less easily with the touch than
with the eye a sphere from an ellipsoid which is nearly
spherical. And besides it is when the touch has been exer-
cised under the control of the sight that it furnishes us with
the most exact ideas, for its results are then confirmed by
those which we possess already in regard to time, motion,
space, and the normal position of bodies, &c. Yet even in
these conditions the sense of feeling may be the source of
error. M tiller says, and rightly too, that by touch we feel not

15

226

THE HUMAN BODY.

the object which touches us, but that part of the tegument
where the contact takes place and the impressions which
it receives. The idea of external objects given by touch
then is, when completely analyzed, the possibility of distin-
guishing the different parts of the body as occupying a
different place in space. The result is, that if the parts of
our bodies are momentarily in an abnormal condition, we
receive, notwithstanding, the sensation in the relative order
that the regions from which these sensations emanate pre-
serve in a normal condition. If, for example, we cause .a
ball to revolve between two fingers of the same hand, we
have the sensation of a single body touching these two
fingers; but if we cross the fingers and place the ball between

Fig- 43-

their extremities, the sensation is that of two balls, each one
rolling in contact with one of the fingers.

The sensations of touch are somewhat persistent, especially
when the tactile impression is joined to that of general sensi-
bility. Thus when we have carried a burden on the shoulder,
or when any part of the body has been subjected to great
and prolonged pressure, we still perceive the sensation some-
time after the weight is removed and the pressure has ceased,
but in such cases the tissues subjacent to the skin take part
in the sensation as well as the skin itself.

The organ of touch may also be the seat of impressions
which are subjective, or which arise from internal causes,
physical or moral. The sight of a striking spectacle or the
emotion caused by a narrative produces in soire persons a

MODIFICATIONS OF FEELING. 227

marked sensation of cold ; the idea of shivering causes an im-
pression which resembles it, and the fear of tickling is suffi-
cient to produce its effects.

Feeling is modified by various influences; cold, or san-
guineous congestion resulting from violent exercise, diminishes
or suppresses for a time the sensibility of the skin ; certain
occupations, by thickening the epidermis, destroy the delicacy
of the touch; and lastly, age diminishes the cutaneous per-
spiration, the epidermis dries up, and the skin no longer has
the suppleness and elasticity which renders the touch so
delicate in youth.

Tactile sensibility is often intensified by disease, and some-
times modified, suspended, or destroyed. We see this in
trances which supervene after, or are provoked under, the in-
fluence of certain nervous affections. Charlatanism, even in
our day, avails itself of this phenomenon, which we confine
ourselves to simply mentioning here.

CHAPTER XVI.

Voice and speech. — Organ of voice ; larynx, cavity of the larynx,
glottis, vocal cords ; the larynx at different ages and in different sexes. —
Physiology of the larynx; mechanism of the voice; opinions as to the
formation of the voice. — Galen, Fabricins Acquapendente, Dodart,
Ferrein, Biot, Milller, Savart, Masson, and Longet. — Theories founded
071 laryngoscopic observations. — Formation of sounds in whistling. —
Voice ; speaking voice, mechanism of articulate sounds, vowels ^ con-
sonants, timbre of the vowels; the tongne as an organ of pronunciation^
— Singing; chest voice, falsetto voice, mixed voice; different theories on the
formation of the falsetto : Milller, M. Segond, M. Longet, M. Fournie,
M. Bataille, M. Mandl. — Timbres of the voice: high pitch, grave pitch.
— Compass of voices : bass, baritone, tenor, contralto, mezzo-soprano,
soprano. — Ventriloquy.

The larynx. — The organ of the voice is a sort of a cartilagin-
ous tube composed of movable pieces articulated together, per-
fectly symmetrical, wider and triangular at its upper portion,
which opens into the pharynx, cylindrical at its lower portion,
where it is continuous with the trachea. It is placed in the
anterior and •middle portion of the neck and below the
hyoid bone, to which it is united by muscles and ligaments,
and in consequence it follows the movements of the hyoid
bone and the tongue, rising and falling with them. Its
movements are connected with deglutition, the acuteness
and gravity of sounds emitted, and with respiration according
as it is diaphragmatic or clavicular (see Respiration, p. 97).

Five cartilages form the skeleton of the larynx; they are

1. The cricoid cartilage (cricos, a ring); it is situated at the
base of the organ, and is attached to the first ring of the
trachea.

2. The thyroid cartilage (thyreos, a buckler), which is com-
posed of two quadrilateral plates, joined together in front

THE LARYNX.

and on the median line. This cartilage protects, as its name
indicates, the organ of the voice. In front a ligament
attaches its lower border to the cricoid cartilage, with which
it is articulated behind; its anterior surface presents at the

Fig. 44.— Section of larynx in the median line.

A. Epiglottis, in front of which the

hyoid bone and base of the
tongue are seen.

B. Thyroid cartilage.

C. Arytenoid cartilage.

E. Anterior portion of cricoid

cartilage.

F. Vocal cord of right side.

G. Ventricle of the larynx.
H. Rings of the trachea.

D. Posterior portion of cricoid cartilage. I. Trachea.

top an angular sloping protuberance, which is more marked
in man than in woman. It forms the projection on the front
of the neck which is called "Adam's apple." The upper
border is united to the hyoid bone by a membrane and
ligaments.

3. The two aryteiwid cartilages (arutaina, a funnel); they-

230 THE HUMAN BODY.

form the posterior and superior wall of the larynx, and come
together behind in the shape of the lip of a ewer; they arti-
culate with the cricoid cartilage, and are united to the thyroid
by muscles and ligaments.

4. The epiglottis (epi, added to, glotta, the tongue) is a sort
of cartilaginous valve, very elastic and mobile, situated a
little below the base of the tongue, and attached to the supe-
rior border of the thyroid cartilage. Its function is to cover
exactly the superior opening of the larynx during deglutition,
so as to prevent the introduction of the food into the air-
passages. When the tongue is brought well forward, and
the base depressed, in some individuals the summit of the
epiglottis is visible.

Numerous muscles attach the larynx to the sternum, to the
hyoid bone, and by this last to the shoulder-blade, to the
tongue, and to the lower jaw; these muscles are called ex-
trinsic^ and move the larynx as one piece. Others, called
intrinsic muscles of the larynx, combine to form its walls,
and to modify its diameter by acting on the cartilages, and
assist in the functions of the glottis. Lastly, the arytenoid
cartilages are united by ligaments to the epiglottis, or to the
thyroid cartilage; these last, the thyro-arytenoid ligaments
form, with the muscles of the same name and with the mucous
membrane, the vocal cords, of which we proceed to speak.

The cavity of the larynx, or its internal surface, does not
correspond in form and dimensions with the external surface;
it is cylindrical at the bottom, triangular at the top; the
dimensions of the lower part are invariable, while those of
the upper portion, on the contrary, are variable in form, from
the mobility of the epiglottis, of the arytenoid cartilages, &c.
About the middle of its height the laryngeal cavity presents
on each side a fold formed by the thyro-arytenoid muscles and
lower ligaments of the same name, and the mucous mem-
brane; these resemble two ribbons of a white colour tinged
with rose, running horizontally from front to back, attached
by their external border and their extremities to the wall of
the larynx, free on the surface and internal border, leaving
an opening between them which is linear, elliptic, or trian-
gular, according to the moment when it is observed, and

GLOTTIS. VOCAL CORDS. 23!

whether we see the whole or only the two anterior thirds.
This opening permits the passage of the air into and out of
the chest, it is called the glottis, the folds which circumscribe
it have been called the vocal cords. About one-third of an
inch higher up there are two other similar but less prominent
folds, they are formed by the superior thyro-arytenoid liga-
ments, and are designated by this name, or by that of the
superior vocal cords (see fig. 44, p. 229). The space between
them has been called the superior glottis, it is larger than the
glottis proper, and does not resemble it in form when exam-
ined by the aid of the laryngoscope. Before this instrument
was invented the larynx was described by anatomists as they
saw it in the dissecting-room, hence the name of superior
glottis, and the likening of this orifice to that of the glottis.

Between the vocal cords proper and the superior thyro-
arytenoid ligaments there is on each side a depression; these
are the ventricles of the larynx; and lastly, a little above these
ligaments is the stiperior opening of the larynx, surmounted in
front by the epiglottis, which is lowered upon, and covers it
completely during deglutition. The space comprised between
the glottis and the superior opening of the larynx is called
the vestibule of the glottis.

Formerly authors were divided in opinion in regard to the
larynx; some gave the name of glottis to all the region
between the level of the inferior and that of the superior
vocal cords, others applied it to the superior glottis, and
others again to the inferior glottis only. This last opinion,
which has been commonly received since the investigations of
Bichat and Boyer, has been confirmed by the laryngoscope,
which demonstrates the existence of a single glottis, and a
single pair of vocal cords.

The internal walls of the larynx are lined with a fibrous
membrane, constituted in part by yellow elastic tissue. This
membrane, which forms the thyro-arytenoid and aryteno-epi-
glottic ligaments, is covered throughout its whole extent by
a mucous membrane, which on the free border of the vocal
cords is very thin and transparent, slightly adherent, and
covered with an epithelium different from that found on the
rest of its surface.

232 THE HUMAN BODY.

The larynx is but slightly developed in early infancy, and
does not differ in its dimensions in the two sexes; and the
characteristics of the voice are the same also. From the t
third to the twelfth year this organ remains nearly stationary;
but about the fourteenth year it almost doubles in size in the
boy, and the voice takes a masculine character. This evolu-
tion is rapid, and is nearly accomplished in the course of a
year, though the larynx is not perfectly developed till the
twenty-fifth year. In girls it augments about a third in size.
The larynx, therefore, of an adult woman is smaller than that
of man, its angles are less prominent, and the glottis is
smaller. These differences are related to the characteristic
pitch, compass, and power, which distinguish the voice of
man from that of woman.

In diaphragmatic respiration the larynx is immovable; but
when the expansion of the chest extends to the upper ribs,
the sternum, and the clavicle, two of the extrinsic muscles
of the larynx assisting in the elevation of the sternum, cause
by their contraction the descent of the larynx, to which they
are attached by their upper extremities. (See Respiration,

P- 97-) .

Physiology of the larynx, mechanism of the voice. — Like most
physiological questions, that of the emission of the voice is
differently explained by writers on that subject. In order to
explain its functions, the larynx has been compared to dif-
ferent musical instruments. Gerdy thought "that we should
do better to endeavour to show that this instrument in man
has no resemblance to any one formed by art." This, doubt-
less, is true; the human larynx is as inimitable in its perfec-
tion as it is admirable in the results it produces; but, in
comparing the most ingenious machines of this character
that man has ever constructed, with the larynx, we do pre-
cisely what Gerdy recommends, for this is the surest means
of establishing its evident superiority. The analogy is besides
incontestable, in spite of the distance which separates an
inert mechanical production from a living organic apparatus,
and it is only by studying the formation of sounds in instru-
ments that we can, if not explain, at least seek to comprehend
their formation in the larynx.

MECHANISM OF VOICE. 233

The vocal apparatus of man is composed of the lungs,
acting as a bellows; the trachea, which conducts the air from
the lungs to the larynx, where the sound is formed; and of
the pharynx, the buccal, and nasal cavities, which increase
the sounds and modify their character.

The air driven through the glottis by the lungs causes a
vibration of the vocal cords, and sound is produced; it is
increased by passing through the upper part of the larynx,
the mouth, and nasal fossae; it acquires more or less volume,
and its character varies according as these cavities are more
or less open and free; but it does not change its nature as
regards the tone. If, for example, the glottis emits a C,
it may be heard as a muffled, a natural, or a nasal sound,
according to the condition in which the cavities are through
which it passes; but the tone does not change, it is always
aC.

Savants have held different opinions on the formation of
sounds in the larynx, and upon the functions of the constitu-
ent parts of the vocal organs. It being impossible to con-
sider all these opinions, or the many experiments which have
been made, the physical laws upon which they were founded,
or which were opposed to them, we shall confine ourselves
to a summary explanation of a few of them.

We may be permitted, however, first to quote from the
Magasin Pittoresque an anecdote which very well illustrates
this point of our subject: —

In 1798 Cuvier, in reading an essay on the voices of birds
before the Academy of Sciences, remarked that some phy-
siologists considered the larynx as a stringed instrument,
others as a wind-instrument. An academician spoke and
denied this distinction, affirming that everybody knew that
the larynx was a wind-instrument. "You are in error," im-
mediately exclaimed another member, "it is a stringed in-
strument."

These two theories have long divided philosophers.

Galen looked upon the glottis as a reed; Fabricius Acqua-
pendente gave a remarkable description of the larynx in the
sixteenth century; he recognized the glottis as the essential
organ of the voice, and compared its action to that of an

-234 THE HUMAN BODY.

organ -pipe; the air in breaking against it produced the
sound, the glottis being less open for acute than for grave
sounds.

Dodart at the end of the seventeenth century, after hesi-
tating between the vibration of the air or the vibration of
the vocal cords as the origin of sound, compares the glottis
to the mouth-piece of a hautboy. This great physiologist, in
giving successive explanations, differing as widely as possible
from each other, of the phenomena of the voice, has advanced
or hinted at most of the theories which have been projected
since his time.

In 1741 Ferrein compared the vocal cords to the strings
of a violin, the air acting as the bow.

Biot could see nothing in the glottis which resembled a
vibrating cord. "The simplest principles of acoustics," said
this illustrious physicist, "are sufficient to make us reject this
strange opinion." Miiller advocated the theory of Ferrein
against that of Biot, and yet he admits with him and with
Magendie, Cagniard de la Tour, G. Weber, and other
learned men, that the glottis is a reed with two membranous
lips vibrating under the action of the air, and producing the
sound by their vibrations.

Sa.vart compared the human glottis to a bird-catcher's
whistle surmounted by a supply-pipe, the cavities of the
whistle being represented by the ventricles of the larynx, the
openings by the interval between the vocal cords. The air
vibrated, he thought, in traversing the inferior glottis, and
divided into two columns against the superior vocal cords,
which act as the stop in an organ-pipe, one of these columns
of air in vibrating causes the resonance of the air in the
ventricles, the other causes the vibration of the air in the
vocal tube. In this last hypothesis it is not the vibration of
the vocal cords, but that of the air which produces the sound.

The theory of Savart on this latter point has been admitted
by Longet and Masson. They believe the sound is pro-
duced at the orifice of the inferior glottis the same as at the
mouth-piece of wind-instruments, by the periodically variable
passage of the air, which becomes the seat of a vibratory
movement. The inferior vocal cords and the ventricles are

MECHANISM OF VOICE. 235

necessary for voice ; the superior vocal cords should be con-
sidered simply as a means of perfection in regard to the
variation and modulation of sounds.

Haller thought the epiglottis had no influence on voice,
but that it permitted the swelling of the sounds into grave or
acute without changing the tone, as did also Magendie and
Biot. Longet thinks that it assists in the expulsion of the
air by the nasal fossae in the production of very acute
sounds, and that it may contribute to the timbre of the voice.

The part of the pharyngeal, buccal, and nasal cavities in
the production and modification of sound is differently stated
by different authors. Savart thought that they regulated the
height of vocal sounds ; they have been considered as sup-
plementary apparatus, and that it is to their peculiar reson-
ance that the quality of the voice is due.

The invention of the laryngoscope, by enabling us to see
the interior of the larynx, has given us exact notions of its
function. It enables us to verify the changes of form, the
appearance of the glottis at different ages, and during the
emission of the voice. This method of studying the larynx
has resulted in late years in works of the greatest interest.

M. Fournie considers the larynx as a membranous reed-
instrument, and the mechanism of the voice, according to
this learned observer, is as follows: — The vocal cords pro-
duce the sound by their vibration, but do not vibrate in their
totality. Fixed in front and at the back, at the level of their
free border, they may be separated by the air, but not caused
to vibrate in their entire thickness, while the mucous mem-
brane which covers their free border, and which adheres only
very slightly, detaches itself under the influence of the passing
air, and thus forms the free vibrating portion of the reed.
On this part only of the larynx the epithelium of the mucous
membrane is of the same nature as that of the membranes
in the other parts of the organism which are subjected to
constant friction, as those of the articulations for example,
and this gives it the power of resisting the friction of the air
and of the vibrations which it causes. In the emission of
the voice the vocal cords are stretched lengthwise and
breadthwise. By producing mechanically this double tension

236 THE HUMAN BODY.

of the vocal cords in the larynx after death, M. Fournie'
obtained all the notes comprised between two octaves.

The ventricles of the larynx are contracted and almost
effaced during the emission of the voice; their function seems
to be to moisten the vocal cords with a mucous fluid, and
to aid in their movements, as well as those of the walls of
the vestibule and glottis.

The superior thyro-arytenoid ligaments adapt the tube
formed by the vestibule of the glottis to the sounds emitted
by the vocal cords. During the emission of sound their
borders are never on the same line as the opening of the
glottis; sometimes they approach the vocal cords, sometimes
they almost disappear, or, on the contrary, enlarge into the
vestibule of the glottis so as almost to fill it. By experiments
on the dead subject, M. Fournie has proved that if these
ligaments are drawn apart during the emission of a note by
the larynx, the sound is lower by one tone; if only one is
drawn aside it falls a semitone. The same result is produced
in all the notes comprised in an octave.

The epiglottis descends and nearly closes the superior
opening of the larynx in grave sounds, and rises more and
more as the sound becomes more acute. In the grave
notes the soft palate permits the sounds to pass through
the mouth and the nasal fossae, and in proportion as the voice
is elevated it rises toward the posterior orifice of the nasal
fossae, so as to prevent the echoing of the sound in these
cavities.

The nasal fossae give exit to the air when the disposition
of the vocal tube is such, in the formation of certain letters,
as more or less to hinder its passage through the mouth. The
isthmus of the throat and the mouth have no influence on
the note, but they perfect and modify its character. The
trachea and bronchia, as well as the vocal tube, resound like
a harmonic table, of which each part corresponds to one of
the notes of the voice; and lastly, the intensity of the sound
is in direct proportion to the force of the impulsion of the
air, to the extent of the vocal cords put in vibration, and to
their tension.

Formation of sounds in u> hist ling. — The study of the for-

WHISTLING. 237

mation of sounds in the glottis includes that faculty which
man possesses of producing the sounds of whistling. This
.is certainly a much less important and less elevated function;
but it is nevertheless very interesting to the physiologist, as
it evidently nearly resembles that of the voice in its me-
chanism.

In order to produce the sound of whistling, the lips form
a real glottis, which Dodart has named the labial glottis. The
opening between the lips varies in form; in the grave tones it
is nearly round in shape, and at its maximum in diameter ; in
the acute sounds it becomes elliptic, and is reduced to a
narrow slit; the tongue regulates the intonation, by approach-
ing more or less to the lower front teeth, touching them in
the acute sounds, and withdrawing itself in the grave sounds.
The space which separates the lips from the teeth varies also,
in the same relative degree, for the same reason. The tongue
sharpens the notes as in flute-playing; the grave sounds may
be produced in drawing in the air, as in breathing; in short,
the sound is acute or intense in proportion to the impulsion
of the air by the lungs.

If a disk of cork be placed between the lips, about one-
fifth of an inch in thickness, with a hole about one line
in diameter in the centre, the sound of whistling can be pro-
duced through this aperture, and modulated the same as
with the lips. Cagniard de la Tour, to whom we are in-
debted for this experiment, concludes from it that the sound
does not proceed from the vibrations of the lips; but has its
origin in those of the air, excited by an intermittent friction
against their walls. Longet and Masson compare the appar-
atus for whistling in man to the whistle of a bird-catcher, and
they find a close analogy between the labial and the laryngeal
glottis.

Fournie' rejects this theory, and supposes the sound of
whistling to be produced by mechanism analogous to that of
an organ-pipe, the air breaking against the stop, which is
represented by the upper incisors. Whichever doctrine we
may accept, it is certain that the lips, or the perforated disk
which replaces them, play an important part in the produc-
tion and modification of sound in ordinary whistling, for

238 THE HUMAN BODY.

when these sounds are made without the aid of the lips, by
a peculiar disposition of the tongue, it is only a single sound.
It is the same in whistling through the teeth with the lips
drawn apart, or when the tongue being doubled, and the
ringers placed in the mouth, we produce an intensely acute
sound, but which cannot be modulated.

In the apparatus for whistling, as in that of the voice, the
functional disposition, and its modifications in relation to the
sounds emitted, takes place by movements under the control
of the will, although they are, so to speak, instinctive. The
changes in the dimensions of the orifices and of the buccal
tube, in the tension of the walls of the mouth, the impulsion
of the air, &c., are all effected instantaneously, and in such a
manner as to produce all the notes. No instrument of music
equals the perfection of this apparatus.

Voice. — Voice is a sound produced in the throat by the
passage of the air through the glottis, as it is expelled from
the lungs. It is grave and strong in man, soft and higher in
woman; it varies according to age, and is developed simul-
taneously with the larynx, as has already been stated. It is
alike in both sexes in infancy, but is modified in youth; then
the voice is said to "change." In the young woman it de-
scends a note or two, and becomes stronger. In the young
man the change is much more strongly marked. At the
fourteenth or fifteenth year the voice loses its regularity, be-
comes harsh and unequal, the high notes cannot be sounded,
while the grave ones make their appearance, and the mascu-
line character of the voice is established. A year is gene-
rally sufficient for this change to be complete, and the voice
of the child gives place to that of the man. Exercise of the
voice in singing should be very moderate, if not entirely sus-
pended, while this change is going on.

Speaking voice. — Voice is divided into singing and speaking
voice. One differs from the other almost as much as noises do
from musical sounds. In speaking, the sounds are too short
to be easily appreciable, and are not separated by fixed and
regular intervals, like those of singing; they are linked together
generally by insensible transitions; they are not united by
the fixed relations of the gamut, and can only be noted with

MECHANISM OF ARTICULATE SOUNDS. 239

difficulty. That it is the short duration of speaking sounds
which distinguishes them from those of singing, is proved by
this, that if we prolong the intonation of a syllable, or utter
it like a note, the musical sound becomes evident. And if
we pronounce all the syllables of a phrase in the same tone,
the speaking voice closely resembles psalm-singing. Every
one must have noticed this in hearing school-boys recite or
read in a monotone, and the analogy is complete when the
last two or three syllables are pronounced in a different tone.
Spoken voice is moreover always a chant more or less marked,
according to the individual and the sentiment which the
words express. The accentuation peculiar to certain lan-
guages also gives the speech the character of a chant : to a
French ear an Italian preacher seems always to sing. It is
a chant also which is caused by all those inflections of the
voice, which express our sentiments and our passions, and
which vary with every thought. They extend from the
feeble murmur, which the ear scarcely perceives, to the
piercing cry of pain. Affectionate, sympathetic, imperious,
or hostile, they sometimes charm, sometimes irritate, and
always move us. It is related of Gretry, that he amused
himself by noting as exactly as possible the "Bonjour, mon-
sieur!" (Good day, sir!) of the persons who visited him; and
these words expressed by their intonation, in fact, the most
opposite sentiments, in spite of the constant identity of the
literal sense. Baron, the comedian, moved his audience to
tears by his recitation of the stanzas of the song, "Si le roi
m'avait donne Paris sa grand* ville" — If the king had given
me Paris his great city.

Mechanism of articulate sounds. — Writers are not in accord
in explaining the pronunciation of letters, that is, the me-
chanism of articulate sounds; but, whether grammarians or
physiologists, they all class the letters according to the parts
of the vocal apparatus which co-operate in their pronuncia-
tion, as labials, dentals, gutterals, &c. The division of the
signs of the alphabet into vowels and consonants expresses
the universal idea that a vowel is a voice, a sound perfect in
itself, while a consonant cannot be sounded without the help
of a vowel associated with it. The consonants, indeed, do

240 THE HUMAN BODY.

not make even a noise, a murmur; but they give a peculiar
character to a vowel sound. We find something in the
playing of an instrument analogous to this function of a con-
sonant. If we pinch the string of a violin, or strike a bell
with a hammer, a sound is produced which we imitate with
the voice by prefixing a / or d, as dinn, tinn; if the string or
the bell be made to vibrate with the bow, the sound as re-
produced by the vocal organ is preceded by the letters cr,
whence the imitative French word crin-criu. The hammer
and bow are the consonants, the note of the bell or the violin
is the vowel.

Helmholtz has demonstrated, as we have already observed
in speaking of hearing, that the timbre of sounds is deter-
mined by the harmonics. He was able by means of ingeni-
ous instruments to decompose the sounds which only produce
a single sensation, and which seem to us simple, though they
are really composed of elementary sounds more or less
numerous. This analysis enabled him to discover the laws
under which the quality of the sounds is constituted which
are emitted by the glottis, and resound in the vocal tube
under the form of vowels. Among the elementary sounds
composing the sound emitted by the glottis, the vocal tube
exalts a particular one by preference, and it is this one
which gives to the vowel its characteristic timbre. The vocal
tube disposes itself in a special form for each vowel. It
lengthens or shortens, dilates or contracts; it places itself, in
a word, in conditions essential to the strengthening of the
sound which determines the timbre. Each vowel is there-
fore characterized by a note, but each one has a particular
affinity for certain notes; it is sometimes difficult, or even
impossible, to give such a note on another vowel than that
with which it corresponds, and thus singers are sometimes
forced to substitute one vowel for another.

In seeking in the different qualities of the voice, and
especially in the vowels, for the seat of the resonance of
sounds in the buccal tube, and the parts which co-operate in
this resonance, Fournie has made a classification of the
letters, which he claims to have rendered more exact and
more anatomical than any of his predecessors. The tongue,

THE VOWELS. THE TONGUE IN SPEECH. 241

the teeth, the lips, and the throat, are the parts by which
most of the letters are formed. To these Fournie adds the
palate for some of them, and the glottis for the 7z, which,
until recently, was classed among the gutturals. It is un-
necessary to remark that in the study of the vowels in their
relation to the mechanism of articulate sounds, the laryngo-
scope has given invaluable aid.

The manner of forming the vowels differs from that of the
consonants in this respect : the parts which co-operate in the
formation of the vowels must be fixed during the utterance
of the vowel, while the articulation of the consonants is
effected by a movement of the parts essential to their forma-
tion. Thus "/," is enunciated by suddenly opening the lips
which have been previously closed; and in the same way
the other consonants are pronounced by some movement;
and this movement is in accordance with the disposition of the
parts necessary to the utterance of the vowel which precedes
or follows the consonant.

Of all the parts which serve for the articulation of sounds,
the tongue is the one which plays the principal part, and
therefore it gives its name to the whole group of modulations
of the voice which constitute language, or as we sometimes
say, a tongue. And yet observation teaches us that the
volume of the tongue may be greatly diminished, or may
even exist only in a rudimentary state, without its being im-
possible to speak.

De Jussieu relates that he saw a girl fifteen years old, in
Lisbon, who was born without a tongue, and yet she spoke so
distinctly as not to excite the slightest suspicion of the ab-
sence of that organ.

The Transactions of the Royal Society of London (1742)
contain a report of the commission which was appointed to
investigate a case of a similar nature. It was a woman
who had not the slightest vestige of a tongue, but who could,
notwithstanding, drink, eat, and speak as well and as dis-
tinctly as any one, and even articulate the words in singing.
Other instances have been known where individuals, after
losing a portion of the tongue by accident or disease, have
again been able to speak after a longer or shorter time.

lo

242

THE HUMAN BODY.

Singing. — We generally recognize two series of sounds in
the voice in singing, one comprising the grave and semi-acute
notes, and the other the high notes; this is called the register
of the voice, one is the chest register or voice, and the other
the head register or voice, or falsetto. Some writers admit a
third series or mixed voice, which resembles a diminutive
chest-voice, in quality and in the disposition of the glottis
when it is produced.

We have indicated already the principal physiological
theories on the formation of the voice in general: there is
no less diversity in opinion in regard to the falsetto. Accord-
ing to Miiller, it results from the vibrations of the edge only
of the vocal cords; other authors incline to the notion that
the glottis no longer vibrates like a reed, but like the mouth-
piece of a flute. M. Segond makes the falsetto voice to come
from the superior glottis exclusively, that is to say, from the
vibration of the superior thyro-arytenoid ligaments. This
opinion has been refuted by the experiments of M. Longet.
And lastly, Weber and Longet attribute the origin of the
falsetto notes to the harmonics of the vocal cords.

The laryngoscope enables us to study the glottis during
the emission of the chest-notes, and even of the falsetto
notes, but observers are not agreed upon the phenomena
which they have observed.

According to Fournie, the chest, the falsetto, and the mixed

Fig. 45. — The glottis and vocal cords.

A, E. Glottis in the chest-voice.
C. Glottis in thefalse-tto voice.

voice, are all produced by the vibration of the mucous fold
which covers the free border of the vocal corcb.

CHEST-VOICE. FALSETTO VOICE. 243

In the chest-voice the larynx descends very low and the
vocal cords are horizontal and stretched simultaneously in
length and thickness; the superior thyro-arytenoid ligaments
project, and partly hide the external border of the vocal
cords; the epiglottis is slightly inclined over the opening of
the larynx; the transverse diameter of the glottis is very
small and linear, and the edges of the vocal cords are very
thick and rigid. The larynx rises in proportion as the tone
grows higher, the epiglottis straightens again little by little;
the plane of the vocal cords inclines; the orifice of the glottis
shuts progressively from behind forward, and consequently
the vibrating portions diminish in length, while at the same
time the tension increases.

In the falsetto, the larynx is carried upward and backward
against the spinal column, the soft palate rises, and its
posterior pillars approach each other, the ventricles of the
larynx are obliterated, the vocal cords are wholly visible, and
their borders are in contact for half their length at least.
The glottis is therefore closed behind, and its orifice, very
much smaller than it was during the utterance of the chest-
notes, diminishes progressively as the notes grow higher.

In the mixed voice the glottis is open throughout its whole
length, and its transverse diameter is greater than for the
other registers.

According to M. Battaille, in the chest-voice the cords
vibrate throughout their extent, the opening of the glottis is
rectilinear, there is less tension in the walls of the vestibule
and glottis, and on the contrary more in the vocal cords,
than in the falsetto voice. In the falsetto voice, the arytenoid
cartilages embrace each other by a sort of reversion in the
two upper thirds of their internal surface, the glottis then
being ellipsoid in form and more open behind than in the
chest-voice.

This form of the glottis, which is attributed by the eminent
artist to the falsetto voice, is precisely the same that M.
Fournie has seen in the mixed voice, which requires less
effort.

M. Battaille is the only author who notes the joining of
the arytenoid cartilages by their internal surface: others

244 THE HUMAN BODY.

admit that they approach each other at their borders only
so as to close the hollow which separates them behind, and
to cause the vocal cords simultaneously to face each other
through part of their length.

M. Mandl has kindly communicated to us the result of
his numerous observations on this subject; according to his
opinion, in producing the chest-voice the arytenoid cartilages
are separated behind; in the falsetto, in a normal condition, they
approach and join each other on their posterior border, which
causes the vocal cords to face each other — as M. Fournie
also says — behind, while they remain separated in front by
the slit of the glottis, which has become elliptic and much
shorter; in certain persons, however, we observe something
analogous to the joining of the arytenoid cartilages which
M. Battaille describes, and which belongs to the normal condi-
tion of the larynx. In fact, when one of these cartilages is
anchylosed at its point of union with the cricoid, and does
not move to meet its congener, the latter supplies the defect
and covers it by a sort of overlapping.

Timbres (the distinctive quality of voices). — Besides that
quality which is peculiar to each individual, the voice may
have several others, some of which, as purity, are due to the
perfection of the entire vocal apparatus, and others, as the
hoarse nasal or guttural quality, arise either from the unskil-
fulness of the singer or from some change in the organ.
There are two forms, however, remarkable because they may
be produced at the will of the artist, these are the muffled
voice and the clear voice. Their names indicate their nature.
In the muffled, the sound is rounder, more velvety, and re-
sembles less the sound of a reed; the pronunciation of the
letters is less distinct and sharp, and the noisy vowels, like
the a and e, incline 4o the timbre of o and u. In the clear
voice the sound is piercing, somewhat noisy, and less agree-
able to the ear. This high key is more common among the
northern nations of Europe, while the graver one is ordinarily
adopted by the singers of the south.

It is generally admitted that the muffled voice is caused
principally by the immobility of the larynx when as low as
possible, and in fact the larynx is usually in that position in

DIAPASON OF VOICES. 245

singing in this tone : though M. Segond has occasionally seen
the larynx as high as possible when this voice was produced.
This voice seems to depend on the narrowing of the buccal
orifice and the isthmus of the throat, coincident with as
great 'a dilatation of the mouth as possible, a disposition
which mufiles and veils the resonance of the sound in the
cavities of the pharynx and vocal tube. If in singing the
letter a, with the mouth wide open, the lips be made slowly
to approach each other, and pressing them together without
extending them, the sound passes from the clear to the
muffled tone, and the vowel a sounds like o. This move-
ment of the lips was very apparent in Mademoiselle Giulia
Grisi in certain high notes, but even her admirable voice was
insufficient to make us pardon her for thus marring features
worthy the pencil of Raphael.

Diapason of voices. — Male voices are divided into bass,
baritone, or singing bass, and tenor. The voices of women
are the contralto, which corresponds to the baritone, mezzo-
soprano, and soprano. The extreme limits of these voices are,
for the base the G below the CC; for the soprano, the
F in alt. or the F of the last octave but one of the piano.'
Mozart heard a singer at Parma who gave the C above.
Ordinary voices do not go beyond two octaves, but celebrated
artists have compassed three and even three and a half
octaves.

Fortunately the prodigious compass of such a voice is not
necessary to entrance a real lover of music. The artist is
always sure to triumph when to correct intonation he joins
sympathetic quality, and, what is rare, that good taste which
will not permit him to sacrifice the expression and the charac-
ter of the music to a desire to shine.

Instrumental music awakens in us the most profound
emotions; we are transported by Baillot's violin or the
orchestra of the Conservatory, but no instrument can equal
the impression produced by a beautiful voice; no instrument
can pretend to those sounds, soft or sharp, passionate or
purely peaceful; none has that variety in quality, those
accents which fascinate us and plunge us into ecstasy. In-
struments and their voices are prodigies of art, but the human

246 THE HUMAN BODY.

voice is living sound, as the glance of the human eye is
animated light.

Ventriloquy. — Those who created the word ventriloquy
evidently believed in a voice produced by some other organ
than the larynx. But in these days every one knows that
what is called ventriloquy consists in concealing the origin
and nature of the voice. The ventriloquist speaks with his
lips nearly closed, and he so modifies the sound of his voice
as to make it seem like that of a child, or a woman; he
makes us believe that it comes from a chimney or a cavern,
from the far distance, from the sky, or from the bowels of the
earth. In the last century the French Academy of Sciences
appointed a commission to study the phenomena of ven-
triloquy in a man exceedingly skilful in the art, but acting in
good faith and making no mystery of his power. It is to
the uncertainty as to the direction of the sounds, and to the
errors into which we are easily led by the organ of hearing,
more than to anything else, that the ventriloquist owes his
success. They may deceive ignorant and credulous people,
but they are generally content to amuse their auditory, and
in that they succeed.

CHAPTER XVII.

Physiognomy; study of it in works of art. — Movements of expression, their
seat. — Colouring of the skin; paleness, redness. — Expression of the
muscles; effort, muscles of the face. — Physiognomy of the senses. — Ex-
pression of the eyes, vision, easy or difficult, blindness. — Expression in
the act of hearing, easy or difficult, hearing of an orator, musical hear-
ing. — Expressions of smell and t.iste. — Expressions relating to the touch.

Physiognomy is generally considered as the expression of
the features of the face, but it is not so limited in its elements.
Attitude, repose or action, fulness or slenderness of form,
proportion, bold or graceful relief, and lastly, health or
disease have, in the entire contour of the body, a significa-
tion which completes that of the face. Physiognomy, there-
fore, is the expression which form and motion give to the
body.

In the Caryatides of the temple of Erectheus, we admire
the calmness and grandeur, the majesty of the draperies, the
simple and grave lines of the figures which support without
effort the marble that seems not to weigh upon them. In
the Caryatides of Puget at Toulon, we see the display of
power in the violently contracted muscles, in the arms which
seek to relieve the head from the burden, under which the
whole body stiffens, and is about to succumb !

Compare a Silenus to the Farnese Hercules. In the old
friend of Bacchus, the form is heavy, obese, and flaccid; it is
the abjectness of drunkenness; in the other, the powerful
muscles, the firm proud attitude, the noble bearing, declare
the tamer of monsters and of vices. The Diana Huntress,
with her sure and rapid step, is the enemy of idleness and
repose ; her manner is severe, and human passion has never

248 THE HUMAN BODY.

throbbed in her virgin breast. The Venus Anadyomene,
graceful, timid, uncertain in manner, shows much more of
feeble humanity.

It is to this profound sense of physiognomy in the great
artists that we owe the lively emotion which the sight of their
master-pieces produces, and the ancients do not, in our judg-
ment, merit the reproach cast upon them for the want of
expression in their heads.

The Greeks, for whom statuary was especially a monu-
mental art, gave* to their faces the calm and dignity of gods,
rather than human passions; therefore the action was quiet,
the lines simple, and the expression of the head in harmony
with that of the body; but when they turned to dramatic
subjects, the few examples which remain enable us to judge
that they were not less admirable in works of this nature.

They no doubt guarded against empty grimaces, and it
was principally in action that they placed the expression;
but can we not read disdainful anger on Apollo's lip? and
is not pride stamped on the features of the Venus of Milo?
does not watchfulness careless of danger look from the eyes
of the Gladiator, and love, almost paternal, rest on the simple,
spiritual head of the Faun and Child? Do we not feel a
mother's pain in the Niobe, see the suffering and the prayer
in the look of the Laocoon? The sculptors of the Renais-
sance imposed the same rule upon themselves before the
works of antiquity were revealed to them. They were fol-
lowed also by the painters, although for them these rules
were less inflexible, and yielded more to details in an art
more nearly allied to living nature.

The artist finds in anatomical physiology, and in physi-
ognomy, useful hints and precise principles; but he rightly
abstains from a rigorous and servile application of them,
for though the physician may find it important to know
the exact function of a certain muscle, the sculptor and
the painter must confine himself to the true but not realistic
expression caused by its contraction. To go beyond this,
which is very easy, is to arrive at that repugnant reality which
certain masters of the Spanish school have not hesitated to
adopt.

MOVEMENTS OF EXPRESSION. 249

Caught from nature by photography, physiological expres-
sion belongs to science, and is invaluable to it: but the artist,
like the poet, remembers that his task is to suggest only,
leaving that to be divined which could not be said or de-
lineated without revolting the spectator.

The movements from which the physiognomy results are
always harmonious, and it is to their unity and concordance
that our impressions are due. The least negligence in this
respect shocks us in a picture like a false note in an orchestra,
while our admiration is unbounded for a work of art in which
nothing is forgotten.

Lethiere paints Brutus at the execution of his sons; the face
and attitude of the consul express only merciless severity, the
folds of the toga are faultless, but the contracted hands
reveal the agony of the father under the inflexibility of the
judge. David represents him to us at the moment when the
bodies of his sons are brought to him. The expression of
the head is fierce, the feet, the left hand, and the whole body
are strongly contracted; the right hand alone is carelessly
bent, and takes no part in this convulsive state.

Movements of expression. — Gratiolet, in his treatise on
physiognomy, groups under this term all the modifications of
form, of colour, &c., which manifest themselves on the sur-
face of the body, under the influence of the most widely dif-
ferent causes. These movements are direct, sympathetic, or
symbolic.

In looking at an object, the action of the eyes, and the
animation which they give to the expression, are direct move-
ments; but if we fix the attention, the body takes part in the
action of the eyes, inclines forward, and seems to wish to
move toward the object observed; these are sympathetic
movements, and when thinking of extreme cold we shiver,
this is a symbolic movement.

The limbs, the trunk, and the head, that is to say, the
gestures and attitude, contribute greatly to complete the
physiognomy, as has already been remarked ; the cavities, on
the contrary, take no part in it, the seat of expression is in
the skin, the muscles, and the eyes.

Colour of the integuments. — The skin, parti cularlv on the

250 THE HUMAN BODY.

face, takes the greatest variety of tints, from a violet red to a
livid pallor, under the influence of physical or moral causes,
which quicken or retard the circulation of the blood; but
besides the colouring of the face, it is the movement of the
muscles, and the expression of the eyes, which gives it a
definite signification.

In a feeble man the motion of the heart is retarded, or
sometimes hurried, as if to make up in the number of its
beats for their want of energy; the blood is not sent to the
surface in sufficient quantity, and the face is pale; but the
languor of form and look denote the cause of the pallor.

Cold causes contraction of the tissues, the circulation is
impeded on the surface of the body, the features seem
pinched, the lips, nose, and cheeks take a livid leaden hue;
chills sometimes shake the limbs and the lower jaw; on the
face, as well as over the whole body, the integument is the
seat of a painful constriction, but the eyes only express suf-
fering. When an assassin reproached Bailly with being
afraid, he replied, "No, my friend, I am cold."

Violent exercise, joy, confusion, fury, all quicken the
action of the heart, and precipitate the movement of the
blood through the teguments, which relax or yield to the
impulsion of the fluid; but the open mouth, the dilated
nostrils, the heaving chest, the strong and rapid respiration,
express, as well as the features, an agitation purely physical,
and we are not tempted to assign a moral cause for the flush
which follows muscular effort. The serenity and expansion
of the features, the smile, the brightness and happiness ex-
pressed in the eye when the face is flushed with joy, have
nothing in common with the downcast eyes, the falling lip,
the muscular weakness, and embarrassed manner of the man
who reddens with confusion. We easily recognize also the
haggard and threatening eyes, the knitted brow, the com-
pressed lips, and the violently contracted or strongly agitated
muscles of a man who is a prey to anger, and in whom the
blood, at first impeded in its course, now in its reaction
forcibly injects the integuments.

We see by these few examples that the colouring of the
skin, varying under the influence of the most diverse causes,

EXPRESSION OF THE MUSCLES. 251

is an important element in physiognomy, though its significa-
tion is doubtful, and must be completed by the expression of
all the other features, or of the body.

Expression of the muscles. — The action of the muscles and
the movements resulting from it, have, on the contrary, a
special character, whether taken as a whole or individually,
in certain muscles of the face. In making an effort, these
movements embrace the whole muscular system, and the
expression which results is more characteristic. When re-
produced by the plastic arts, it strongly impresses the spec-
tator, who feels a sort of sympathetic contraction, but which
soon fatigues and irritates like all inconstant attitudes.

The muscles of the face by their single or combined con-
traction cause the most widely differing expressions, and
correspond to all the sentiments, whether simple or complex.
Thus, the muscle of the forehead raises the brow in attention,
admiration, or astonishment; that of the eyebrow contracts
it with pain ; the great zygomatic raises the angle of the lips
in laughing; the triangular muscle of the lips draws them
downward in weeping; other muscles co-operate in expres-
sing combativeness, fear, anger, irony, &c., in short, the
slightest phase of feeling is reproduced in the features, by
the slight or energetic contractions of the muscles, which
carry with them the skin to which they are intimately united,
wrinkling or distending it. An eminent physiologist, M.
Duchenne of Boulogne, particularized the action of these
muscles in expressive movements. But though some of
them may play a distinct part in the mimicry of the face,
others always join in the movements when the sentiment or
sensation acquires a certain vivacity; thus the muscle of the
eyebrow alone may express a certain degree of suffering, but
when it becomes intense the eyelids close, the nostrils dilate,
and other signs beside prove the simultaneous action of the
different muscles. For the physiologist and the physician,
rigorously exact facts of this sort have the greatest value;
but they are of less consequence to the artist, who must repre-
sent not only the muscle but the whole of the parts, near or
distant, to which its action extends. If it is necessary for
him to understand anatomy and the function of the muscles

252 THE HUMAN BODY.

in order to reproduce exactly their projection during move-
ments of the body and limbs, it is much more the study of
the living model which guides him when endeavouring to
render the expression of the features; and if he fails in this,
it is less from ignorance of anatomy than from lack of senti-
ment or incapacity.

It is remarkable also how much opinion varies in regard
to works of art. Each individual brings to their examination
the predisposition of his studies; and if the naturalist may
sometimes criticize justly, sometimes also in his judgments
the artistic sentiment is replaced by the rigorous formulas
and exact notions of science; he does not consider that the
artist should avoid being as exact as a Chinese copy, anci
that a profound artistic sentiment should be completed in
its expression by its' counterpart in the spectator. And lastly,
a savant may be a man of genius, and still lack all artistic
sentiment. Gratiolet, that fine and noble mind, could see
nothing in Raphael's "Creation" but a "deplorable work — a
furious old man striving with feet and hands to separate two
thick clouds." The man who criticized one of the most
admirable master-pieces of art in these terms, was a scholar
of the first order, a great physiologist, and has left a wrork
on physiognomy itself marked by the most delicate percep-
tions and the most profound study.

Physiognomy of the senses. — The more the mind predomin-
ates over matter, and separates itself from it, the more elevated
will be the expression of the physiognomy. Faith and
prayer transport man into an order of ideas purely intellec-
tual, and give to the features a character in which sense has
no part. Resignation attaches itself to the terrestrial affec-
tions, and mingles with them an element of pain which,
whether moral or physical, is always expressed by the marks
of suffering. The recital of a dishonourable action adds a
shade of disgust to indignation, and the moral impression
seems to affect our organs as they are affected by material
impressions.

This indirect and, as it were, figurative action of the senses
on the physiognomy, mingles incessantly with movements of
another order, and often expresses itself with as much energy

EXPRESSION OF THE EYE. 253

as the real sensations. When these latter are acute they
govern the expression almost as completely as the most
violent passions, and may, like them, impress upon the
features the sign of an infirmity, a fault, or a vice.

Our senses, as has been already stated, are united by the
constant relations of complementary or sympathetic functions,
as the sight and the touch, the sight and the hearing, the
taste and the smell frequently control or complete each other
by their simultaneous action, and often all the senses are in
action at once. This coincidence of the sensations reflected
by the physiognomy is a source of varied and complex expres-
sions, as much so as the nervous impressions transmitted to
the brain can be, and to describe the physiognomy of any
one sense it is necessary almost to draw all the features of
each of the other senses.

The eye gives an expression of intelligence to the physiog-
nomy, and reflects the thought more than any other organ of
the senses. It is especially through the eye that the passions
reveal themselves — that joy or sorrow, courage or fear, envy,
love, or hate, frankness or duplicity, are expressed on the
features; therefore, says one, if you would know a man's
sentiments, read them in his eyes.

The movements of the globe of the eye, its fixity, and the
contraction or dilatation of the pupil, infinitely vary the ex-
pression of the face, and give to the whole of the features a
decided meaning; but to the mimic language of the globe
the eyelids bring an important and often decisive addition.

When sight is good, attention is expressed without effort:
the face is calm; the eyelids, moderately open, show the globe
of the eye, which fixes itself on the object, follows it in space,
and acts, in short, as do all the organs in a normal condi-
tion, without any consciousness; but if, on the contrary, it
is necessary to distinguish an object which is perceived with
difficulty, the eyelids approach each other, the eyes twinkle,
and the immobility of the body, the suspended respiration",
denote more marked attention; the brow contracts, and the
features wear an expression of pain, which sometimes gives
short-sighted persons a forbidding character.

The face of a blind man is rarely sad, but the immobility

254 THE HUMAN BODY.

of the features, which are so animated by vision, produces a
painful contrast.

In hearing the attention is also more or less characteristic.
If we wish to distinguish a distant noise, or perceive a sound,
the head inclines and turns in such a manner as to present
the external ear in the direction of the sound, at the same
time the eyes are fixed and partially closed. The movement
of the lips of his interlocutor is the usual means by which
the deaf man supplies the want of hearing; the eyes and the
entire head, from its position, have a peculiar and painful
expression of attention. In looking at the portrait of La
Condamine it was easily recognized as that of a deaf person.
Even when hearing is perfect the eyes act sometimes as
auxiliaries to it; in order to understand an orator perfectly,
it seems necessary to see him — the gestures and the expres-
sion of the face seem to add to the clearness of the words.
The lesson of a teacher cannot be well understood if any
obstacle is interposed between him and the eyes of the listen-
ing pupil.

That species of intoxication which we term ecstasy is ex-
pressed on the features of a musical amateur on hearing a
master-piece; all the powers of attention are concentrated on
one organ; the features are slightly contracted by the smile
or other expression in accordance with the character of the
music; the eyes are half shut or closed, though sometimes
they are fixed agonizingly on the singer in some difficult pas-
sage, or enthusiastically on some leader, like Habeneck,
leading his orchestra with a passionate gesture.

If a piercing, harsh, or discordant sound strikes the car,
the eyes close, and at the same time the lips, the nose, and
the whole face contract as if the other senses were combining
to protect the hearing from the pain it endures, and against
which its immovable organ cannot defend it. It is impatient
suffering, and no longer the charm of a delicious sensation.

Under the influence of the smell and the taste the expres-
sion of the physiognomy is extremely varied, and reflects
perfectly the delicacy or the force of the sensation, the
degree of pleasure which accompanies it, or the horror and
repugnance which it excites in us. Here, as in hearing,

EXPRESSION OF TOUCH. 255

sympathetic movements are combined with the direct move-
ments produced in the affected organs. When taste is con-
cerned, it is very rare that they are not confounded, for
almost always the aroma is combined with the taste, and
either perfects its excellence or renders it still more insup-
portable. But whether it expresses satisfaction or antipathy,
the play of the physiognomy in sensations of this nature has
nothing elevated in it, rather it unveils a certain abasement
of the individual; hearing and sight are in immediate con-
nection with the most precious faculties of the mind, while
taste and smell appeal specially and directly to our material
appetites. But we must not therefore judge too severely the
elation- of a gourmand seated at a well-spread table. The
best compliment he can oifer to his host is to show a worthy
appreciation of an exquisite repast. We shall see the spirit
of our guest, vivified by the sweet influence, shine from his
eyes with a light which will easily enable us to pardon what
little of sensuality there is in his mouth.

It is by the sense of touch that we acquire clear ideas of the
form of bodies, of the distance, resistance, weight, tempera-
ture, &c. It confirms the testimony of our eyes, and joins
its impressions to those of sight often in an effective manner,
and always through the mind.

The touch produces expressive movements in us then, in
connection with our tactile or visual sensations; and these
movements are sometimes direct, as in effort, and sometimes
sympathetic and an indication of the impressions produced
on the skin. Lastly, touch is the origin of symbolical move-
ments by which we express the thought of bringing an ob-
ject near, or putting it away from us. To this sense are re-
lated the gestures which accompany our words. WTe affirm
a fact by so placing the hand as if we would rest it firmly on
a body; we deny by a gesture putting the false or erroneous
proposition away from us; we express doubt by holding the
hand suspended, as if hesitating whether to take or reject.
When we part from dear friends, or greet them again after
long absence, the hand extends towards them as if to retain,
or to bring them sooner to us. If a recital or a proposition
is revolting, we reject it energetically in gesture as in thought.

256 THE HUMAN BODY.

In a friendly adieu we wave our good wishes through space
to him who is the object of them; but when it expresses
enmity, by a brusque movement we sever every tie. The
open hand is carried backward to express fear or horror, as
well as to avoid contact; it goes forward to meet the hand of
friendship; it is raised suppliantly in prayer toward Him
from whom we hope for help; it caresses lovingly the downy
cheek of the infant, and rests on its head invoking the bless-
ing of Heaven; in a word, the touch, real or imaginary, is
constantly adding a feature to the physiognomy.

THE END,

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