OUR BODILY FRAME
Fundamental Importance of Anatomy--Human Anatomy--Hippocrates,
Aristotle, Galen, Vesalius--Comparative Anatomy--Georges
Cuvier--Johannes Müller--Karl Gegenbaur--Histology--The Cellular
Theory--Schleiden and Schwann--Kölliker--Virchow--Man a
Vertebrate, a Tetrapod, a Mammal, a Placental, a Primate--Prosimiæ
and Simiæ--The Catarrhinæ--Papiomorphic and Anthropomorphic
Apes--Essential Likeness of Man and the Ape in Corporal Structure
All biological research, all investigation into the forms and vital
activities of organisms, must first deal with the visible body, in
which the morphological and physiological phenomena are observed. This
fundamental rule holds good for man just as much as for all other
living things. Moreover, the inquiry must not confine itself to mere
observation of the outer form; it must penetrate to the interior, and
study both the general plan and the minute details of the structure.
The science which pursues this fundamental investigation in the
broadest sense is anatomy.
The first stimulus to an inquiry into the human frame arose, naturally,
in medicine. As it was usually practised by the priests in the older
civilizations, we may assume that these highest representatives of
the education of the time had already acquired a certain amount
of anatomical knowledge two thousand years before Christ, or even
earlier. We do not, however, find more exact observations, founded
on the dissection of mammals, and applied, by analogy, to the human
frame, until we come to the Greek scientists of the sixth and fifth
centuries before Christ--Empedocles (of Agrigentum) and Democritus
(of Abdera), and especially the most famous physician of classic
antiquity, Hippocrates (of Cos). It was from these and other sources
that the great Aristotle, the renowned "father of natural history,"
equally comprehensive as investigator and philosopher, derived his
first knowledge. After him only one anatomist of any consequence is
found in antiquity, the Greek physician Claudius Galenus (of Pergamus),
who developed a wealthy practice in Rome in the second century after
Christ, under the Emperor Marcus Aurelius. All these ancient anatomists
acquired their knowledge, as a rule, not by the dissection of the human
body itself--which was then sternly forbidden--but by a study of the
bodies of the animals which most closely resembled man, especially the
apes; they were all, indeed, comparative anatomists.
The triumph of Christianity and its mystic theories meant retrogression
to anatomy, as it did to all the other sciences. The popes were
resolved above all things to detain humanity in ignorance; they rightly
deemed a knowledge of the human organism to be a dangerous source
of enlightenment as to our true nature. During the long period of
thirteen centuries the writings of Galen were almost the only source
of human anatomy, just as the works of Aristotle were for the whole
of natural history. It was not until the sixteenth century, when the
spiritual tyranny of the papacy was broken by the Reformation, and the
geocentric theory, so intimately connected with papal doctrine, was
destroyed by the new cosmic system of Copernicus, that the knowledge
of the human frame entered upon a new period of progress. The great
anatomists, Vesalius (of Brussels), and Eustachius and Fallopius
(of Modena), advanced the knowledge of our bodily structure so much
by their own thorough investigations that little remained for their
numerous followers to do, with regard to the more obvious phenomena,
except the substantiation of details. Andreas Vesalius, as courageous
as he was talented and indefatigable, was the pioneer of the movement;
he completed in his twenty-eighth year (1543) that great and systematic
work _De humani corporis fabrica_; he gave to the whole of human
anatomy a new and independent scope and a more solid foundation. On
that account he was, at a later date, at Madrid--where he was physician
to Charles V. and Philip II.--condemned to death by the Inquisition as
a magician. He only escaped by undertaking a pilgrimage to Jerusalem;
in returning he suffered shipwreck on the Isle of Zante, and died there
in misery and destitution.
The great merit of the nineteenth century, as far as our knowledge of
the human frame is concerned, lies in the founding of two new lines
of research of immense importance--comparative anatomy and histology,
or microscopic anatomy. The former was intimately associated with
human anatomy from the very beginning; indeed, it had to supply the
place of the latter so long because the dissection of human corpses
was a crime visited with capital punishment--that was the case even
in the fifteenth century! But the many anatomists of the next three
centuries devoted themselves mainly to a more accurate study of the
human organism. The elaborate science which we now call comparative
anatomy was born in the year 1803, when the great French zoologist
Georges Cuvier (a native of Mömpelgard, in Alsace) published his
profound _Leçons sur l'anatomie comparée_, and endeavored to formulate,
for the first time, definite laws as to the organism of man and the
beasts. While his predecessors--among whom was Goethe in 1790--had
mainly contented themselves with comparing the skeleton of man with
those of other animals, Cuvier's broader vision took in the whole
of the animal organization. He distinguished therein four great and
mutually independent types: Vertebrata, Articulata, Mollusca, and
Radiata. This advance was of extreme consequence for our "question
of all questions," since it clearly brought out the fact that man
belonged to the vertebral type, and differed fundamentally from all
the other types. It is true that the keen-sighted Linné had already,
in his _Systema Natuae_, made a great step in advance by assigning
man a definite place in the class of mammals; he had even drawn up
the three groups of half-apes, apes, and men (_Lemur_, _simia_, and
_homo_) in the order of primates. But his keen, systematic mind was
not furnished with that profound empirical foundation, supplied by
comparative anatomy, which Cuvier was the first to attain. Further
developments were added by the great comparative anatomists of our own
century--Friedrich Meckel (Halle), Johannes Müller (Berlin), Richard
Owen, T. Huxley, and Karl Gegenbaur (Jena, subsequently Heidelberg).
The last-named, in applying the evolutionary theory, which Darwin had
just established, to comparative anatomy, raised his science to the
front rank of biological studies. The numerous comparative anatomical
works of Gegenbaur are, like his well-known _Manual of Human Anatomy_,
equally distinguished by a thorough empirical acquaintance with their
immense multitudes of facts, and by a comprehensive control of his
material, and its philosophic appreciation in the evolutionary sense.
His recent _Comparative Anatomy of the Vertebrata_ establishes the
solid foundation on which our conviction of the vertebral character of
man in every aspect is chiefly based.
Microscopic anatomy has been developed, in the course of the present
century, in a very different fashion from comparative anatomy. At
the beginning of the century (1802) a French physician, Bichat, made
an attempt to dissect the organs of the human body into their finer
constituents by the aid of the microscope, and to show the connection
of these various _tissues_ (_hista_, or _tela_). This first attempt
led to little result, because the scientist was ignorant of the one
common element of all the different tissues. This was first discovered
(1838) in the shape of the _cell_, in the plant world, by Matthias
Schleiden, and immediately afterwards proved to be the same in the
animal world by Theodor Schwann, the pupil and assistant of Johannes
Müller at Berlin. Two other distinguished pupils of this great master,
who are still living, Albert Kölliker and Rudolph Virchow, took up
the cellular theory, and the theory of tissues which is founded on
it, in the sixties, and applied them to the human organism in all its
details, both in health and disease; they proved that, in man and
all other animals, every tissue is made up of the same microscopic
particles, the _cells_, and these "elementary organisms" are the real,
self-active citizens which, in combinations of millions, constitute
the "cellular state," our body. All these cells spring from one simple
cell, the _cytula_, or impregnated ovum, by continuous subdivision.
The general structure and combination of the tissues are the same in
man as in the other vertebrates. Among these the mammals, the youngest
and most highly developed class take precedence, in virtue of certain
special features which were acquired late. Such are, for instance, the
microscopic texture of the hair, of the glands of the skin, and of the
breasts, and the corpuscles of the blood, which are quite peculiar to
mammals, and different from those of the other vertebrates; man, even
in these finest histological relations, is a _true mammal_.
The microscopic researches of Albert Kölliker and Franz Leydig (at
Würzburg) not only enlarged our knowledge of the finer structure of man
and the beasts in every direction, but they were especially important
in the light of their connection with the evolution of the cell and
the tissue; they confirmed the great theory of Carl Theodor Siebold
(1845) that the lowest animals, the Infusoria and the Rhizopods, are
unicellular organisms.
Our whole frame, both in its general plan and its detailed structure,
presents the characteristic type of the vertebrates. This most
important and most highly developed group in the animal world was
first recognized in its natural unity in 1801 by the great Lamarck;
he embraced under that title the four higher animal groups of
Linné--mammals, birds, amphibia, and fishes. To these he opposed the
two lower classes, insects and worms, as invertebrates. Cuvier (1812)
established the unity of the vertebrate type on a firmer basis by
his comparative anatomy. It is quite true that all the vertebrates,
from the fish up to man, agree in every essential feature; they all
have a firm internal skeleton, a framework of cartilage and bone,
consisting principally of a vertebral column and a skull; the advanced
construction of the latter presents many variations, but, on the whole,
all may be reduced to the same fundamental type. Further, in all
vertebrates the "organ of the mind," the central nervous system, in
the shape of a spinal cord and a brain, lies at the back of this axial
skeleton. Moreover, what we said of its bony environment, the skull,
is also true of the brain--the instrument of consciousness and all the
higher functions of the mind; its construction and size present very
many variations in detail, but its general characteristic structure
remains always the same.
We meet the same phenomenon when we compare the rest of our organs with
those of the other vertebrates; everywhere, in virtue of heredity,
the original plan and the relative distribution of the organs remain
the same, although, through adaptation to different environments,
the size and the structure of particular sections offer considerable
variation. Thus we find that in all cases the blood circulates in
two main blood-vessels, of which one--the aorta--passes over the
intestine, and the other--the principal vein--passes underneath, and
that by the broadening out of the latter in a very definite spot a
heart has arisen; this "ventral heart" is just as characteristic of all
vertebrates as the "dorsal heart" is of the articulata and mollusca.
Equally characteristic of all vertebrates is the early division of
the intestinal tube into a "head-gut" (or gill-gut), which serves in
respiration, and a "body-gut" (or liver-gut), which co-operates with
the liver in digestion; so are, likewise, the ramification of the
muscular system, the peculiar structure of the urinary and sexual
organs, and so forth. In all these anatomical relations _man is a true
vertebrate_.
Aristotle gave the name of four-footed, or tetrapoda, to all the higher
warm-blooded animals which are distinguished by the possession of two
pairs of legs. The category was enlarged subsequently, and its title
changed into the Latin "quadrupeda," when Cuvier proved that even
"two-legged" birds and men are really "four-footed"; he showed that the
internal skeleton of the four legs in all the higher land-vertebrates,
from the amphibia up to man, was originally constructed after the same
pattern out of a definite number of members. The "arm" of man and the
"wing" of bats and birds have the same typical skeleton as the foreleg
of the animals which are conspicuously "four-footed."
The anatomical unity of the fully developed skeleton in the four limbs
of all tetrapods is very important. In order to appreciate it fully
one has only to compare carefully the skeleton of a salamander or a
frog with that of a monkey or a man. One perceives at once that the
humeral zone in front and the pelvic zone behind are made up of the
same principal parts as in the rest of the quadrupeds. We find in all
cases that the first section of the leg proper consists of one strong
marrow-bone (the _humerus_, in the forearm; the _femur_, behind);
the second part, on the contrary, originally always consists of two
bones (the _ulna_ and _radius_, in front; the _fibula_ and _tibia_,
behind). When we further compare the developed structure of the foot
proper we are surprised to find that the small bones of which it is
made up are also similarly arranged and distributed in every case: in
the front limb the three groups of bones of the forefoot (or "hand")
correspond in all classes of the tetrapoda: (1) the _carpus_, (2)
the _metacarpus_, (3) the five fingers (_digiti anteriores_); in the
rear limb, similarly, we have always the same three osseous groups of
the hind foot: (1) the _tarsus_, (2) the _metatarsus_, and (3) the
five toes (_digiti posteriores_). It was a very difficult task to
reduce all these little bones to one primitive type, and to establish
the equivalence (or homology) of the separate parts in all cases;
they present extreme variations of form and construction in detail,
sometimes being partly fused together and losing their individuality.
This great task was first successfully achieved by the most eminent
comparative anatomist of our day, Karl Gegenbaur. He pointed out,
in his _Researches into the Comparative Anatomy of the Vertebrata_
(1864), how this characteristic "five-toed leg" of the land tetrapods
originally (not before the Carboniferous period) arose out of the
radiating fin (the breast-fin, or the belly-fin) of the ancient
fishes. He had also, in his famous _Researches into the Skull of the
Vertebrata_ (1872), deduced the younger skull of the tetrapods from the
oldest cranial form among the fishes, that of the shark.
It is especially remarkable that the original number of the toes (five)
on each of the four feet, which first appeared in the old amphibia
of the Carboniferous period, has, in virtue of a strict heredity,
been preserved even to the present day in man. Also, naturally and
harmoniously, the typical construction of the joints, ligaments,
muscles, and nerves of the two pairs of legs has, in the main, remained
the same as in the rest of the "four-footed." In all these important
relations _man is a true tetrapod_.
The mammals are the youngest and most advanced class of the vertebrates.
It is true they are derived from the older class of amphibia, like
birds and reptiles: yet they are distinguished from all the other
tetrapods by a number of very striking anatomical features. Externally,
there is the clothing of the skin with hair, and the possession of
two kinds of skin glands--the sweat glands and the sebaceous glands.
A local development of these glands on the abdominal skin gave
rise (probably during the Triassic period) to the organ which is
especially characteristic of the class, and from which it derives its
name--the _mammarium_. This important instrument of lactation is made
up of milk glands (_mammae_) and the "mammar-pouches" (folds of the
abdominal skin); in its development the teats appear, through which
the young mammal sucks its mother's milk. In internal structure the
most remarkable feature is the possession of a complete diaphragm, a
muscular wall which, in all mammals--and _only_ in mammals--separates
the thoracic from the abdominal cavity; in all other vertebrates
there is no such separation. The skull of mammals is distinguished
by a number of remarkable formations, especially in the maxillary
apparatus (the upper and lower jaws, and the temporal bones). Moreover,
the brain, the olfactory organ, the heart, the lungs, the internal
and external sexual organs, the kidneys, and other parts of the body
present special peculiarities, both in general and detailed structure,
in the mammals; all these, taken collectively, point unequivocally
to an early derivation of the mammals from the older groups of the
reptiles and amphibia, which must have taken place, at the latest, in
the Triassic period--at least twelve million years ago! In all these
important characteristics _man is a true mammal_.
The numerous orders (12-33) which modern systematic zoology
distinguishes in the class of mammals had been arranged in 1816
(by Blainville) in three natural groups, which still hold good as
sub-classes: (1) the monotrema, (2) the marsupialia, and (3) the
placentalia. These three sub-classes not only differ in the important
respect of bodily structure and development, but they correspond, also,
to three different historical stages in the formation of the class,
as we shall see later on. The monotremes of the Triassic period were
followed by the marsupials of the Jurassic, and these by the placentals
of the Cretaceous. Man belongs to this, the youngest, sub-class; for
he presents in his organization all the features which distinguish
the placentals from the marsupials and the still older monotremes.
First of all, there is the peculiar organ which gives a name to the
placentals--the _placenta_. It serves the purpose of nourishing the
young mammal embryo for a long time during its enclosure in the
mother's womb; it consists of blood-bearing tufts which grow out of the
chorion surrounding the embryo, and penetrate corresponding cavities in
the mucous membrane of the maternal uterus; the delicate skin between
the two structures is so attenuated in this spot that the nutriment in
the mother's blood can pass directly into the blood of the child. This
excellent contrivance for nourishing the embryo, which makes its first
appearance at a somewhat late date, gives the foetus the opportunity
of a longer maintenance and a higher development in the protecting
womb; it is wanting in the _implacentalia_, the two older sub-classes
of the marsupials and the monotremes. There are, likewise, other
anatomical features, particularly the higher development of the brain
and the absence of the marsupial bone, which raise the placentals above
all their implacental ancestors. In all these important particulars
_man is a true placental_.
The very varied sub-class of the placentals has been recently
subdivided into a great number of orders; they are usually put at from
ten to sixteen, but when we include the important extinct forms which
have been recently discovered the number runs up to from twenty to
twenty-six. In order to facilitate the study of these numerous orders,
and to obtain a deeper insight into their kindred construction, it
is very useful to form them into great natural groups, which I have
called "legions." In my latest attempt[9] to arrange the advanced
system of placentals in phylogenetic order I have substituted eight
of these legions for the twenty-six orders, and shown that these may
be reduced to four main groups. These, in turn, are traceable to one
common ancestral group of all the placentals, their fossil ancestors,
the _prochoriata_ of the Cretaceous period. These are directly
connected with the marsupial ancestors of the Jurassic period. We
will only specify here, as the most important living representatives
of these four main groups, the rodentia, the ungulata, the carnivora,
and the primates. To the legion of the primates belong the prosimiæ
(half-apes), the simiæ (real apes), and man. All the members of these
three orders agree in many important features, and are at the same
time distinguished by these features from the other twenty-three
orders of placentals. They are especially conspicuous for the length
of their bones, which were originally adapted to their arboreal manner
of life. Their hands and feet are five-fingered, and the long fingers
are excellently suited for grasping and embracing the branches of
trees; they are provided, either partially or completely, with nails,
but have no claws. The dentition is complete, containing all four
classes--incisors, canine, premolars, and molars. Primates are also
distinguished from all the other placentals by important features in
the special construction of the skull and the brain; and these are the
more striking in proportion to their development and the lateness of
their appearance in the history of the earth. In all these important
anatomical features our human organism agrees with that of all the
other primates: _man is a true primate_.
An impartial and thorough comparison of the bodily structure of the
primates forces us to distinguish two orders in this most advanced
legion of the mammalia--half-apes (_prosimiae_ or _hemipitheci_) and
apes (_simiae_ or _pitheci_). The former seem in every respect to be
the lower and older, the latter to be the higher and younger order. The
womb of the half-ape is still double, or two-horned, as it is in all
the other mammals. In the true ape, on the contrary, the right and left
wombs have completely amalgamated; they blend into a pear-shaped womb,
which the human mother possesses besides the ape. In the skull of the
apes, just as in that of man, the orbits of the eyes are completely
separated from the temporal cavities by an osseous partition; in
the _prosimiae_ this is either entirely wanting or very imperfect.
Finally, the cerebrum of the _prosimia_ is either quite smooth or very
slightly furrowed, and proportionately small; that of the true ape is
much larger, and the gray bed especially, the organ of higher psychic
activity, is much more developed; the characteristic convolutions
and furrows appear on its surface exactly in proportion as the ape
approaches to man. In these and other important respects, particularly
in the construction of the face and the hands, _man presents all the
anatomical marks of a true ape_.
The extensive order of apes was divided by Geoffroi, in 1812, into
two sub-orders, which are still universally accepted in systematic
zoology--New World and Old World monkeys, according to the hemisphere
they respectively inhabit. The American "New World" monkeys are called
_Platyrrhinae_ (flat-nosed); their nose is flat, and the nostrils
divergent, with a broad partition. The "Old World" monkeys, on the
contrary, are called collectively _Catarrhinae_ (narrow-nosed); their
nostrils point downward, like man's, and the dividing cartilage is
narrow. A further difference between the two groups is that the
tympanum is superficial in the _platyrrhinae_, but lies deeper,
inside the petrous bone, in the _catarrhinae_; in the latter a long
and narrow bony passage has been formed, while in the former it is
still short and wide, or even altogether wanting. Finally, we have a
much more important and decisive difference between the two groups in
the circumstance that all the Old World monkeys have the same teeth
as man--_i. e._, twenty deciduous and thirty-two permanent teeth
(two incisors, one canine, two premolars, and three molars in each
half of the jaw). The New World monkeys, on the other hand, have an
additional premolar in each half-jaw, or thirty-six teeth altogether.
The fact that these anatomical differences of the two simian groups
are universal and conspicuous, and that they harmonize with their
geographical distribution in the two hemispheres, fully authorizes
a sharp systematic division of the two, as well as the phylogenetic
conclusion that for a very long period (for more than a million years)
the two sub-orders have been developing quite independently of each
other in the western and eastern hemispheres. That is a most important
point in view of the genealogy of our race; for man bears all the marks
of a _true catarrhina_; he has descended from some extinct member of
this sub-order in the Old World.
The numerous types of _catarrhinae_ which still survive in Asia and
Africa have been formed into two sections for some time--the tailed,
doglike apes (the _cynopitheci_) and the tailless, manlike apes (the
_anthropomorpha_). The latter are much nearer to man than the former,
not only in the absence of a tail and in the general build of the body
(especially of the head), but also on account of certain features
which are unimportant in themselves but very significant in their
constancy. The sacrum of the anthropoid ape, like that of man, is made
up of the fusion of five vertebræ; that of the _cynopithecus_ consists
of three (more rarely four) sacral vertebræ. The premolar teeth of
the _cynopitheci_ are greater in length than breadth; those of the
_anthropomorpha_ are broader than they are long; and the first molar
has four protuberances in the former, five in the latter. Furthermore,
the outer incisor of the lower jaw is broader than the inner one
in the manlike apes and man; in the doglike ape it is the smaller.
Finally, there is a special significance in the fact, established by
Selenka in 1890, that the anthropoid apes share with man the peculiar
structure of the discoid _placenta_, the _decidua reflexa_, and the
pedicle of the allantois. In fact, even a superficial comparison of
the bodily structure of the _anthropomorpha_ which still survive makes
it clear that both the Asiatic (the orang-outang and the gibbous ape)
and the African (the gorilla and chimpanzee) representatives of this
group are nearer to man in build than any of the _cynopitheci_. Under
the latter group we include the dog-faced papiomorpha, the baboon,
and the long-tailed monkey, at a very low stage. The anatomical
difference between these low papiomorpha and the most highly developed
anthropoid apes is greater in every respect, whatever organ we take
for comparison, than the difference between the latter and man.
This instructive fact was established with great penetration by the
anatomist Robert Hartmann, in his work on _The Anthropoid Apes_;[10]
he proposed to divide the order of _Simiae_ in a new way--namely, into
the two great groups of _primaria_ (man and the anthropoid ape) and the
_simiae_ proper, or _pitheci_ (the rest of the catarrhinæ and all the
platyrrhinæ). In any case, we have a clear proof of _the close affinity
of man and the anthropoid ape_.
Thus comparative anatomy proves to the satisfaction of every
unprejudiced and critical student the significant fact that the body of
man and that of the anthropoid ape are not only peculiarly similar, but
they are practically one and the same in every important respect. The
same two hundred bones, in the same order and structure, make up our
inner skeleton; the same three hundred muscles effect our movements;
the same hair clothes our skin; the same groups of ganglionic cells
build up the marvellous structure of our brain; the same four chambered
heart is the central pulsometer in our circulation; the same thirty-two
teeth are set in the same order in our jaws; the same salivary,
hepatic, and gastric glands compass our digestive process; the same
reproductive organs insure the maintenance of our race.
It is true that we find, on close examination, certain minor
differences in point of size and shape in most of the organs of man
and the ape; but we discover the same, or similar, differences
between the higher and lower races of men, when we make a careful
comparison--even, in fact, in a minute comparison of the various
individuals of our own race. We find no two persons who have exactly
the same size and form of nose, ears, eyes, and so forth. One has
only to compare attentively these special features in many different
persons in any large company to convince one's self of the astonishing
diversity of their construction and the infinite variability of
specific forms. Not infrequently even two sisters are so much unlike
as to make their origin from the same parents almost incredible. Yet
all these individual variations do not weaken the significance of the
fundamental similarity of structure; they are traceable to certain
minute differences in the growth of the individual features.