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| [[File:Mark_Hill.jpg|90px|left]] This 1932 paper by Keith are two presentations in his series of six Hunterian Lectures given in 1932 and is an historic description of abnormalities in human development.
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'''Modern Notes:''' [[Neural Abnormalities]] | [[Neural Development]] | [[Pharyngeal Arches]] | [[Spinal Cord Development]]

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{{Historic Disclaimer}}
MALFORMATIONS OF THE HUMAN BODY FROM A NEW POINT or VIEW

SIR ARTHUR KEITH’S HUNTERIAN TLECTIIJRES

The following are the first two of a series of six abstracts
of Hunterian Lectures delivered in January at the Royal
College of Surgeons of England  Sir Arthur Keith,
F .R.S., Conservator of the Museum.

I.—MALFORMATIONS OF THE BRAIN AND SPINAL CORD

i In the earlier stages of development, operations which
are in many respects comparable to those performed by
surgeons are carried out automatically by the tissues of
the human embryo. Pre—natal surgery might be described
as knifeless, bloodless, and surgeonless. When prep-natal
operations fail—and modern_research is throwing much
light on whythey sometimes fail—children are born with
defects which may be so grave that life isvimpossible.
But even the lesser defects tax the ingenuity of the
modern surgeon. , I , _ . C .

_ The greatest "of these developmental operations carried
out in the embryo relate to the enclosure of the entire
nervoussystem of the human body. Thanks to the combined labours of embryologists, we are now able to follow
the rapid sequence of events ' which brings about the
enclosure of brain and spinal cord from forehead to rump_.
Although the human brain is by far the most complex
structure known to us, it and the spinal cord are in reality
a greatly transformed wide strip of skin which runs along
the back of the embryo. ..,It,.is a remarkable fact that,
although the brain is only needed after birth, yet it is
the first of all bodily structures to become differentiated,
appearing even before the heart has become functional,
and when the embryo is less than one-twenty-fifth of an

inch long. In this early period the skin of thelback is being modified to form nerve ‘plates.

. Medical menlhave becomelsofamiliar with the details
of the operation which encloses the nervous system that
they are apt to forget the merits of Nature as a surgeon.‘
Two conditions are necessary in everyday surgery: the
parts which are to unite must be brought into apposition
-_—that condition is dependent on the surgeon. Theother
condition is that the parts so broughtgtogetherpmust have
the power to unite by healing ; this power is inherent in
all living tissues, particularly -in those of the embryo.
When the embryo enters the fourth week of development
the margins of the nerve plate along the back begin to
rise up, so that first a trough is ‘ formed and then a
tube. The folded margins of the tubebegin to come‘ in‘
contact at the region of the neck ; edge‘ becomes healed‘
to edge, just as in a wound, except that there is noscar,
left to mark the site. From the neck» thepprocess of
union spreads forwards and backwards. In less than a

week» it has reached the site of the forehead, and in less '

than two weeks it has reached the lower ‘region of the
trunk. ' In less than two weeks the whole of man’s central
nervous system becomes submerged in an orderly manner,
and the line of submergence is obliterated by a covering
of skin—a major operation in plastic surgery is successfully and automatically carried out.» .4 . .. —

_But Nature’s operation may fail completely ; the child
then comes into the world with the brain and spinal cord
exposed on the head and back as ﬂat plates. More frequently the failure is partial—the lower part of the spinal
cord being left exposed——constituting the defect known as
spina bifida. We are coming to a knowledge as to why
an operation——usually carried out with the utmost success
by Nature, or by powers inherent in the tissues—does

MALFORMATIONS OF THE BRAIN AND SPINAL CORD

' ——to injurious inﬂuences.


sometimes fail. Spina bifida. can be produced experimentally in the developing eggs of fish and frog by subjecting them——when the neural plates arebeing enclosed
By such means any ‘wound can‘
be kept open. ‘ j V ’ p ‘ C '

.The formation of the. ‘eye also entails‘ two operations
carried out by developmental surgery. They are minor
operations compared with that which segregates the brain
from the embryonic skin. Although they failmuch less
frequently than that" connected with theicentral nervous
system, they are much more instructive from asurgical
point of view, for it was while experimenting with the
rudiments of the eye that‘ embryologists discovered some
of the secrets of developmental surgery. An eye arises
by part of the embryonic tube growing out sideways as
a pocket to form the retina. VVhen the closed end of the
neural or retinal pocket comeseagainst the skin of the
embryonic head, the area of skin" so touched begins to
behave curiously. It grows inwards in the form of a

pocket,’ which abuts’ against the nerve pocket‘ or out
i growth. Both pockets become shut off——the one from the

embryonic skin to form the lens of the eye, the other
from the neutral tube to form the sensitive lining of the
eyeball. So perfectis the healing at the point where the

lens pocket becomes detached from the skin that not a,

Indeed, that part of the skin becomes the
VVhen the first stages of eye

trace is left.
clear cornea of the eye.

formation are ‘completed, one side of the eyeball still

remains open ; this fissure is closed by aprocess similar
to that which unites the two sidesof a wound, Sometimes union of the fissure of the eyeball is imperfect,
giving rise to the defect known as coloboma.

It was in connexion with the development of the eye

_ that embryologists made the first of a series of discoveries

which "are letting us’ into some of Nature’s surgical
secrets. It was found that the brain pocket which grows
out.to form the retina is a “T master tissue ”—-‘one possessing’ almost magical qualities. If it is prevented..from
coming in contact’ with the embryonic skin, or is cut
away before it reaches the skin, then the lens-forming area
of skin remains quiescent, and no lens pocket is ‘formed.
But if the neural pocket be detached, and then be
embedded beneath any area of skin of the embryo, then
the overlying skin at once begins to‘ form a pocket and a
lens.’ The neural pocket possesses this magical power
because of a growth—controlling substance formed within
it. Magic of a similar kind is known to everyone who
has studied the formation of "gallson plants and trees.
Lately Professor Spemann of Freiburg discovered that
a certain small area of tissue on the back of the very
young embryo has these magical or morphogenetic

qualities to a much more wonderful degree than even the

retinal pocket. I Ifa graft is taken of this central tissue,

and if it be implanted ‘on the side of the embryo, then
_. the surrounding tissue, which in ordinary course would
»have become part of» the body wall, now begins to form

a nerve plate and- a new embryo. The key tojsome of

Nature’s secret surgical processes, carried out as routine

proceeding in building. up the embryonic body, will be
foundin a knowledgeof her morphogenic substances. In
the matter of repair Nature is still the master. surgeon.

. The elaborate lining of the internal ear, which provides
the essential machinery of hearing, begins as an area of
exposed skin on the side ‘of the head of the embryo.
Through a series of growth and healing processes the area
becomeslsubmerged in the form of a pocket, the mouth
healinglover and leaving no trace of the original opening.
The lecturer knew of no instance in man where the
auditory pocket had failed to close, yet in certain fishes
it remained open. This was one of the minor discoveries
made by John Hunter, founder of the Museum of the
‘Royal College of Surgeons.


Although the surgeon’s immediate interests were confined to making good Nature's failures, he could not help
speculating on how the elaborate operations just described
had come into being. It was quite evident that no kind
of vertebrate animal could have lived with its nervous
system spread out as open medullary plates on head
and back, exposed to every injury. To find such
a stage of evolution one has to turn to the lowest of
invertebrate forms of life, where the nerve system is
still essentially a part of the skin. The elaborate growth
and extension of the nerve system seen in the vertebrate
animal became possible only when provision had been
made for the earlier stages of development being gone
through in positions of shelter and nurture. With the
elaboration of intrauterine life all forms of developmental
extensions and elaborations became possible. When we
see a human child born with its nerve plates still exposed

from head to sacrum, we are in reality witnessing a 
reversion to a stage of evolution which our ancestors
went through long before the coal measures were laid
down.

Ii.——Malformations Of The Face And Mouth

Nature, in carrying out her evolutionary projects, has
resorted to operations nearly akin to those carried out by
modern surgeons. In the formation of the face of all
animals which suckle their young two such operations
are carried out. Even as late as the seventh week the
human foetus has no roof to its mouth ; the mouth—the
chewing and sucking chamber—is continuous with the
nasal and breath chamber. By the beginning of the third
month a ﬂeshy shelf has grown out from each side of the
mouth ; the edges of these shelves, coming into apposition
along the middle line of the roof of the mouth, unite
together by a process similar to that seen in the healing
of a wound. The operation proceeds automatically, and
is finished in the space of ten days. If it fails, then the
condition of cleft palate results, and the surgeon has to
make good Nature's failure. Cleft palate interferes with
sucking, mastication, and speech. Many of the lion cubs
formerly born in the Zoological Gardens, London, suffered
rom cleft palate. By altering the diet of the lionesses——
as suggested by Sir John Bland-Sutton——giving them a
plentiful supply of vitamins and better surroundings, the
occurrence of these defects has been prevented.

Thanks to the labours of Dr. Robert Broom amongst
the fossil animals preserved in very early geological formations (Permian and Triassic) of South Africa, we know that
the evolutionary movement which ended in shutting the
month off from the nose began very many millions of
years ago. Amongst these South African fossil forms
there occur mammal-like reptiles. Dr. Broom and Professor Watson of University College, London, have traced
the evolution of the palatal plates from mere side ledges,
until they meet in the middle line of the roof of the mouth
and form a complete bony palate. The evolution of the
palate, which occupied aeons of time, is repeated in the
course of ten days in the face of the human foetus.

The appearance of a bony roof in the _mouths of South
African mammal-like reptiles was part of a revolutionary
movement which overtook the jaws of the ancestors of
true mammals. fifty years ago we knew that the lower
jaw of mammals had somehow, and at some remote date,
become hinged to the base of the skull in a new way, and

that the old hinge—the one which continues to serve in .

reptiles-—became incorporated in the ear. How such a
transformation in structure and function took place was an
enigma until the discovery of the South African mammallike reptiles. In them several stages of the transformation
have been found——the new joint coming into being and

serving for purposes of hearing. In the Museum of the
Royal College of Surgeons there are two human lower
jaws which reproduce both hinges—the new mammalian
and the old reptilian.

If as yet we know little of the growth-controlling
mechanisms which make such evolutionary changes
possible, we do clearly realize the functional significance
of the change. With a bony roof to the mouth and .1
new hinge to the lower jaw, mastication became possible.
Mechanical preparation of the food, formerly thrust on
the stomach, was taken over by the teeth and jaws.
VVith the development of a palate sucking became possible.
Nay, it is not unlikely, when we consider how Nature has
lavished her inventive resources on behalf of the young,
that the primary purpose was to permit the immature
young to be suckled.

At a still earlier date another evolutionary operation
was carried out in the face of vertebrate animals—one
still to be observed in the face of every human foetus
during the latter part of the seventh week of development.
If this operation fails, then there results the condition
known as “'hare-lip ”—-where one or both nostrils communicate by a single or a double cleft with the roof of the
mouth. The first stage in establishing an open communication between nose and mouth is still perpetuated in
certain fishes ; with the evolution of air-breathing forms
this open trough between nose and mouth became covered
over. In the course of development the edges came
together, and a process of union, similar to that seen in
a wound, united their opposing edges. Thus a respiratory
passage was established through the nose to the mouth.
The surgeon, in carrying out an operation for the repair
of “ hare—lip ” in a human infant, is repeating a process
which was introduced during the evolution of the lowest
and earliest air-breathing vertebrate animals.

“ Hare-lip ” and “ cleft palate,” the commonest maldevelopments of the human face, may be regarded as
relapses .pr reversions to states which prevailed in the
infancy of vertebrate animals, but there are other defects
which cannot be so explained. There is the condition of
“ cyclops,” where both eyes, in place of being separated
by the bridge of the nose, are fused together to form one
eye under the forehead. The degree of fusion varies. The
nose may be absent altogether, or it may form a ﬂeshy,
proboscis—like structure just over the median eye. The
lower jaw may be absent altogether, so that the ears meet

in front of the neck, and the mouth is reduced to a mere‘

pin-hole. VVe have no reason to believe that at any point
of man’s long ancestral chain there was ever a form with
a median single eye, a proboscis-like nose, a pin-hole
mouth, and ears which met where the chin should be.
These cyclopean monsters can be produced to order in the
developing eggs of fish and newt.
brain—the part to which nose and eyes are attached——is the last to be developed in the growth of the embryonic
head. If, when this final stage is being reached, the
developing embryo be subjected to injurious conditions,
then development is arrested before the right and left
eye buds and nose buds have separated. It is under such
conditions that human cyclopean monsters are produced,
and fortunately they never live. They can never have

produced progeny, and yet they occur to-day just as they

did in the time of the ancient Greeks.

.__
—_

-1
,1

The Department of Scientific and Industrial Research
has now issued its report for the year 1930-31.
(Cmd. 3989, H.M. Stationery Office, 3s. net.) This is
divided into the following main sections: report of the
Committee of the Privy Council for Scientific and
Industrial Research; report of the Advisory Council;
summary of the work of the research organizations of
the Department; and information concerning research

the bones of the old hinge being allocated to the ear and 5 associations.

The front part of the’