Paper - Malformations of the human body from a new point of view 3+4
Keith A. Malformations of the human body from a new point of view: 3. Umbilicus - 4. Testes. (1932) Br. Med. J. .
|Embryology - 26 Mar 2019 Expand to Translate|
|Google Translate - select your language from the list shown below (this will open a new external page)|
العربية | català | 中文 | 中國傳統的 | français | Deutsche | עִברִית | हिंदी | bahasa Indonesia | italiano | 日本語 | 한국어 | မြန်မာ | Pilipino | Polskie | português | ਪੰਜਾਬੀ ਦੇ | Română | русский | Español | Swahili | Svensk | ไทย | Türkçe | اردو | ייִדיש | Tiếng Việt These external translations are automated and may not be accurate. (More? About Translations)
|Historic Disclaimer - information about historic embryology pages|
|Embryology History | Historic Embryology Papers)|
Malformations of the Human Body from a New Point of View
Sir Arthur Keith’s Hunterian Lectures
The following are the second two of a series of six abstracts of Hunterian Lectures delivered in January at the Royal College of Surgeons of England by Sir Arthur Keith, F.R.S., Conservator of the Museum.
III. — MALDEVELOPMENTS AT THE UMBILICUS
Some forty years ago Sir John Bland-Sutton wrote an interesting and important book to prove that in making her great evolutionary advances Nature had at times used methods which were akin to those of disease; An illustration of this truth was to be seen in the human body during the second and third months of its development. During this period of time a developmental hernia was produced at the umbilicus, and within the umbilical sac, outside the cavity of the abdomen, the greater part of the intestines underwent differentiation and growth. During the period in which the intestines occupied their hernial sac, preparations were being carried forwards within the abdomen for their proper and ﬁnal ﬁxation there. For the “ radical cure of hernia in men and women an operation had to be performed. The sac had to be cut open, its contents pressed back into the abdomen, and the opening at which the rupture had occurred had to be sutured, and thus closed. It was interesting to compare the modern surgeon’s method of treating hernia
with that which had been discovered by Nature. At the end of the third month of development the hernia at the umbilicus is cured automatically in the space of a few days ; the intestines are drawn back into the abdomen, and the opening closed. For a knowledge of these processes anatomists are indebted to the very exact investigations made in recent years by Professor J. E. S. Frazer. The processes which here play the part of surgeon are represented by the living, growing tissues of the body.
In the ﬁrst place, there is an expansion of the walls of the abdomen by growth, so that room is made within for the intestine; in the second place, the mesenteries which attach the intestine to the hinder wall of the abdomen shorten and widen their attachments. By these differential processes of growth the intestines are ﬁnally drawn within the abdomen. The withdrawal always takes place in a ﬁxed and orderly manner. In this way the hernia, after having served a -developmental purpose, is cured, but sometimes there is a failure. One child in every 3,000 is born with an uncured hernia at the navel, and it then becomes the duty of the surgeon to mend Nature’s failure. Sometimes the failure is so gross that
the whole contents of the abdomen protrude, presenting a state in which treatment is beyond surgical resources.
Although the surgeon gives his chief thoughts to the
discovery of the best means of treating congenital hernia
of the umbilicus, he cannot help inquiring how herniation at the umbilicus had become introduced as a normal process in the development of higher animals. The key to the problem lies not with the human embryologist, but with the comparative anatomist. The series of events which rendered human beings liable to umbilical hernia commenced in the infancy of vertebrate animals. It began when a part of the intestines had to undergo a premature development to contain a store of yolk which would provide the developing ﬁsh or frog with a supply of nourishment until the immature animal had reached a state to fend for itself. The developingbowel of the dog—ﬁsh grows over, envelops, and encloses its stock of yolk. In its earlier stages it swims with its purse or bag of nourishment suspended from its body. The yolk sac has an outer covering supplied by the body wall. The young ﬁsh is born with a congenital hernia. As the yolk sac empties, the hernia is reduced, leaving no scar or trace behind. When land-living, air-breathing, vertebrate animals were evolved the skin which covered the yolk sac became more important than the sac itself. By a precocious develop- ment and an enormous expansion of that part of the body wall which covered the yolk sac a hood or envelope was formed. This hood, as it expanded, grew over and enclosed the developing embryo in a double covering or envelope—-an outer and an inner. If we do not know as yet the manner in which the miracle of bringing these protective envelopes into being was performed, we do clearly see theuse and need of the inner envelope. It contains water in which the delicate tissues of the embryo are submerged, and by which they are supported. Eggs of ﬁsh and frog can develop only if surrounded and supported by a ﬂuid medium. By the precocious development of part of the covering of the body wall Nature elaborated an inner envelope to serve as a bath in which the higher vertebrate embryo could develop in sheltered circumstances and an outer envelope to serve as a lung for the exchange of air. When a chick is hatched it leaves behind it in the shell the parts of the body which represent the original coverings of the yolk sac. The navel or umbilicus marks the point of detachment. Part of the body wall has been sacriﬁced for the development of the individual ; the umbilical scar is the token of the sacriﬁce.
In higher mammals, particularly in that strange group of which man is a member, matters are carried a. stage further. In the earlier stages of development all efforts are expended on a precocious and extensive formation of that part of the body wall which in lower vertebrates -——reptiles and birds-—forms the envelopes round the body of the embryo. Development within a rigid shell and development within a living, moving, contractile womb require very different methods of procedure. The develop- ing human egg has to burrow into the lining membrane of the womb, and in this position throw out its envelopes ——its inner envelope, the amnion, and its outer, the chorion. During this early period, from the eighth to the fourteenth day, the embryo itself remains in abeyance ; all efforts are expended on the development of the coverings and placenta, which have been evolved out of that part of the body wall which covers the yolk sac of ﬁsh and frog. The epithelial covering of the skin becomes the wildly growing and devouring trophoblast. Part of the body wall becomes drawn out to form the umbilical cord. At birth, the child parts company with cord and coverings4with all that part of its body wall which served the purposes of maintaining the intrauterine life of the infant—and the scar formed at the point of separation becomes the umbilicus. lWhen we remember that the umbilical cord is in "reality an extension of tissue originally designed to form part of the wall of the abdomen, we need not be surprised that at a certain stage of development the cord is occupied by coils of intestine. Nor need we marvel,’ when we consider the elaborate processes connected with the withdrawal of the intestines from the sac, that children should occasionally be born with a developmental hernia still unreduced.
IV. The Migration Of The Testes
Embryology, the study of thegdeveloping human-embryo, has entered on a new era. Eighty years ago Sir Richard Owen taught that Nature, in fashioning the animal body, worked to plan-_—much as builders obey an architect's speciﬁcation. Then came Darwin, who convinced us all that every embryo is its -own architect, that the powers which play the part of surgeon.
-point of view, of very recent origin. T introduced after the, mammalian stock had Tmade T, its appearance in the world. The male gland migrates in shape the unfolding embryo are resident in its developing T
tissues. In later Victorian times, although most embryo- logists had accepted Darwin’s teaching, they still attempted to explain developmental events as the result of mechanical happenings—of foldings and of bendings. It is only in quite recent years that embryologists began
to escape from the bondage of mechanical interpretation. A
The way of escape was opened for them when it was discovered that parts of a living embryo could be detached and maintained alive and studied in various substances, just as bacteria can be kept alive and studied in cultural media. A It was found that certain parts contain growth-controlling substances, by virtue of which they can compel neighbouring tissues to co—operate in producing a new and functional structure. In the light of this new knowledge, we have to revise many of ‘our older conceptions regarding
the development of the human embryo.‘
There is scarcely an operation performed by modern
surgeons that has not its parallel in the earlier stages of . development. TExtenTsive plastic operations are carried
out ; parts are, shifted, altered in shape, or entirely removed ; mendings are effected, and even amputations performed. In all these operations the tissues themselves But even in Nature's operating theatre there are occasional failures.
One of the commonest of the developmental devices used in the production of new structures is that of producing pockets or herniae. Irl the previous lecture it was pointed out that a hernia or rupture was purposely kept open at the umbilicus during thesecond and third months of development, and that it was closed and cured early in
the fourth month. On ' the other hand, a hernia or
rupture is produced in each groin of a human foetus during the latter half of intrauterine life. T foetus this operation is carried out more completely than
in any other of thehigher mammals. The extrusion of the male gland from the body. cavity is, from an evolutionary most mammals, but by no means in all of them. In some it descends only for a special season ; at the end A of that
season the gland ‘returns within the abdomen, and the hernia is automatically reduced.
In other orders of mammals the testes remain permanently within the abdomen, as is the case in birds, reptiles, amphibia, and fish.” ,Even now we are not certain why this genital exodus is‘ made, but this amount we do know. V If the exodus does‘ not occur in man——and the statement holds true for sheep, goat, dog, horse, and bull-—t.h'e gland rarely becomes’
perfectly functional ; it usually. atrophies, if it does not
escape from the abdomen. T Evidence has been brought forward in support of the theory that the atrophy is due
to the higher temperature which ‘prevails within the
abdomen, but on the evidence of comparative anatomy one would suspect that it is the high. intra-abdominal .press,ur_e’s . rather than a high intra-abdorninal temperature
that cause the damage. One cannot suppose that the elaborate machinery which is utilized in bringing about the exodus of the testes was introduced for a slight or unimportant reason, for, without doubt, this develop- mental operation has - made’ the groin -of man a source of weakness to him.
Let us see how_ theinguinal hernia is brought about by developmental means. Although John Hunter wrote his account of the events concerned more than a century and a half ago, his description is, Tin my opinion, still the nearest to fact. In the fourthmonth, just as the umbilical hernia is being reduced, the inguinal hernia begins to be produced. At this time a fold of peritoneum passes from the lower end of the male gland to the inner wall of the
In the human groin. The tissue within the fold begins to grow, and gradually assumes the form of a peritoneum-covered plug. The lower end of the plug reaches the groin, and the peritoneum over its lower end expands into a process like the ﬁnger of a glove. The tip of this peritoneal pocket grows against the belly wall, and as it grows the tissues recede and expand in‘ front of it. Growing plug and ' peritoneal process bring about growth‘ changes of all
the tissues in the body wall, and a tunnel is thus fashioned
for the’ passage of the testis. To permit the testis to follow the advancing. gubernaculum or growth-plug, all the vessels descending to it, its duct, the surrounding
peritoneum to which the testis is anchored, have to be elongated so as to accommodate themselves to the migration. They undergo a plastic reorganization to permit the movement to take place. The whole series of structures forms an advancing army, by which the testis is
guided to the tunnel opened in the belly wall by the
gubernacular plug. It is true, however, that there are original strands in the belly wall which guide the plug towards the scrotum. The testis enters the tunnel in the belly wall at the beginning of the seventh month ; by the end of that month it has made its exit ; by the end of the ninth month it should have reached the close of its journey, and become lodged within the fundus of the scrotum. All the phenomena we can explain only when we presume a growth movement——a co-ordinated operation
T in which gubernaculum, peritoneum, vessels, tissues of the
belly wall, and attachments of the testicle participate. It is a mass movement brought about by an elaborate co-ordination in the growth and atrophy of all the parts concerned. When the migratory movement is over, the
peritoneum and the. subperitoneal tissue which surround
the point of exit immediately set about the repair of the If repair fails, then there is a possibility of an escape of other ‘contents of the abdomen, and the production of a real or acquired hernia. The phenomena which attend the ‘descent of the testicle cannot be explained on any simple mechanical principle; all the resources of organized growth and repair are involved.
iJohn Hunter notonly recognized the anatomical means which were involved in bringing about the migration of the testes," but he was two -centuries ahead of the rest of the world- in understanding the nature of the movement‘ and T how it was 1 brought about. It is the case. that he « assignedf failure of descent to an
imperfection ” of the testis which re'maine'd.witThin the abdomen. Now, it ‘is true
Tthat an arrested testis? may mature ; we are also certain
that a testis whichiwill atrophy if left in the abdomen "will
.mature if translated to the scrotum by surgical lmeans.
Nevertheless, in the light of modern knowledge, we may well assume that the failure is due to an imperfection, if not of the testis, then of the growth-controlling mechanism which brings the descent about. We are coming by some knowledge of how substances’ formed in the ovary and in the pituitary work remarkable growth changes on uterus, vagina, and mammary glands. Now, the earliest scrotal formation known to us occurs at the inguinal end of the mammary ridge. We know how substances formed in the testis can cause, and also alter, the growth of dozens of parts of the body—‘of beard, larynx, brain—in fact, of every part of the body. TVVas Hunter, then,’ so far wrong when he associated the failure of descent of the testis to an imperfection in the growth-controlling mechanism which is centred round the male gland of generation? No one can survey the elaborate organization by which a herniation of the body wall is produced, and by which a’ massive translation of all the testicular parts is brought about, without being convinced that it is the result, not of any simple mechanical means, but of an elaborate series of growth processes.
Cite this page: Hill, M.A. (2019, March 26) Embryology Paper - Malformations of the human body from a new point of view 3+4. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Paper_-_Malformations_of_the_human_body_from_a_new_point_of_view_3%2B4
- © Dr Mark Hill 2019, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G