No. 3313.

FEBRUARY 26, 1887.THE LANCET,

ABSTRACTS OF THE

Crasmas Wilson LecturesON

EVOLUTION IN PATHOLOGY.Delivered at the Royal College of Surgeons of England,

BY J. BLAND SUTTON, F.R.C.S.,ASSISTANT-SURGEON TO THE MIDDLESEX HOSPITAL.

LECTURE III.

REVERSION OR ATAVISM (GER. R1JCKSC13LAG.MB. PRESIDENT AND GENTLEMEN, - By reversion or

atavism is usually understood a tendency in the offspringto resemble its grandparents or more remote ancestors

instead of its immediate parents. To the consideration ofthis interesting and important subject the present lecturewill be devoted, but attention will be more particularlydirected to reversion as it affects structural aberrations.Few persons competent to form an opinion on the matter

will deny that in the embryological history of a given ianimal we read a brief epitome of its ancestry-in fact, its Ievolution, Nothing represents this so forcibly as the fol-lowing quotation from Von Baer: " In my possession aretwo little embryos in spirit, whose names I have omittedto attach, and at present I am quite unable to say to whatclass they belong. They may be lizards or small birds, orvery young mammalia, so complete is the similarity in themode of formation of the head and trunk in these animals.The extremities are still absent in these embryos; but evenif they had existed in the early stage of their development,we should learn nothing, for the feet of lizards and mam-mals, the wings of birds, no less than the hands and feet ofman, all arise from the same fundamental form." This

striking passage from the writings of the great father ofembryology has been rendered more forcible by the effortsof modern investigators in this the most difficult of all

departments of biology.Structural aberrations of congenital origin must be divided

into three main classes: 1. Persistent foetal conditions.2. The attainment of a functional or more or less full deve-lopment of structures which for a given animal are nor-mally suppressed during embryonic life. 3. Malformations:spurious atavism. Each of the three classes will be con-sidered in detail.

1. Per,sistent fcetal conditions.-To this class belong thevarious forms of cleft palate, whether it vary from a bifiduvula to a cleft extending the whole length of the roof ofthe mouth. In fish the buccal and nasal cavities are a com-mon chamber; in lizards and most birds the hard and softpalates are normally cleft, whilst in the young kangaroothe uvula is bifid. The funicular pouch of the peritoneumis a case in point. Normally it becomes closed in its abdo-minal segment, leaving the tunica vaginalis testis as anisolated sac. Frequently it fails to obliterate in any of itscourse. In this respect it conforms to the condition of thepouch found in the majority of mammalia. Up to the pre-sent time, although I have examined all the more importantmammals specially in regard to this point, I have never yetfound the pouch closed. Sometimes it will only admit athin probe, but in others the index-finger could be easilyaccommodated in the peritoneal recess. Numerous examplessuggest themselves of arrest in development-e.g., malfor-mations of heart, uterus, intestinal canal, &c

2. The attainment of a functional or more or less fulldevelopment of structures which for a given animal aresuppressed durin.q embryonic life.-In my first lecture-thaton suppression of parts-a number of examples were givenof organs or parts of organs which became arrested duringembryonic life, which later on may serve as germs of variouspathological growths. In this place we shall have to dealwith certain of these structures in a functional condition.It is important for us to bear in mind that, as Gegenbaurpoints out,l "atavism consists not in the existence of alatent germ, but in its becoming perfected and further1 Polydactyly as Atavism. Morph. Jahrbüch, Bd. vi., S. 584. See

also Journal of Anatomy and Physiology, vol. xvi., p. 615.

developed." The facts relating to the os centrale of thecarpus, as described in the first lecture, is a good exampleof what is to be understood by the preceding sentence. Itis also essential to bear in mind that in the majority ofcases of reversion the atavistic parts do not belong to formspalaeontological1y remote or systematically far distant.(Hensel, Gegenbaur.) In the case of the os centrale weknow that it occurs among the higher apes, for the orangand gibbon present this bone well pronounced in the carpus.The clearest instance, and one which is also interesting, isthat furnished by the manus of the horse. It is a well-established fact that Hipparion, the immediate ancestor ofthe modern horse, possessed three functional toes of thecharacter represented in Fig. 8. Hensel’s investigationsappear to show that the inner toe was the last to abortwhen the equine manus assumed the condition shown in.Fig. 9. Theoretical reasons would lead us to suppose thatif any of these toes reappeared as abnormalities, the onewhich was the last to disappear would be that mostfrequently represented atavistically. This is precisely whatoccurs, and numerous specimens preserved in museums andreported in periodical literature attest the fact. By far themost remarkable of these cases is that reported by Marsha 2in an important paper on " Horses recent and extinct." Herehe gives an excellent account of a case exhibited as theCuban pony, in which this inner digit had reappeared in afunctional form on both hind and fore limbs. The skeletonof a manus of this nature is given in Fig. 9. In such casesas these there seems to be little difficulty in clearly assigningthe deformity to atavism; but that the difficulty may notbe under-estimated, let the student carefully consider the

Fir. 8. FIG. 9. FIG. 10.

FiG. 8.—The manu3 of Hipparion, with three functionaltoes.

FiG. 9. -The manus of a horse with an extra digit func-tional. (After Marsh.)

FiG. 10.- The manus of the modern horse. One toefunctional.

remarks made further on regarding another mode by whichthe horse may acquire an additional functional digit.In the spider monkeys the thumb is usually representedby a mixture of fibrous and cartilaginous tissue, yet aperfectly developed thumb is occasionally developed inthese quadrumana.

3. Spurious atavism.-Twenty years ago, anyone writingupon this subject and regarding abnormalities such as wehave been considering as reversions to lower forms wouldhave been looked upon in a very unfavourable light. Fortu-nately the aspect of things has changed, and the discussionof such matters is admissible even in polite conversation.It is exceedingly necessary to guard against running intothe opposite extreme, for there is a decided tendency at thepresent time, when anything unusual occurs in the con-formation of the parts of an animal, to find out some corre-sponding condition in lower animals, and at once to pro-nounce it as a reversion. This is, of course, erroneous, andan attempt will be made to bring under notice some examplesof this false and unsatisfactory form of reasoning. One ofthe clearest instances known to me is that abnormality ofthe stomach called congenital contraction. Why it shouldbe termed congenital is not very evident, since no anatomistor pathologist who has studied this matter or describedspecimens of this nature makes any mention of such acondition being found in the feetus or young child. Atypical form of the malformation is represented in Fig. 11.We see midway between the pylorus and cardiac ex-

tremity of the stomach a contraction which divides theviscus in two distinct parts, causing it to resemble some-what a rudimentary condition of the complex stomach of

2 American Journal of Science and Art, 1879.I

406

the runu.na.ut, ur na ttpjjruttch rabiktr to that ot the geuusCervulus. Carefully bearing in our minds that a reversionconsists in a reappearance of a lost character, we shall have toshow phylogenetically that man’s immediate ancestors pos-sess such a stomach; but we know full well that a complexviscus of the character exhibited by the ruminant stomachis an exceedingly specialised arrangemnt, reaching itsmaximum among this division of the Ungulata, and in itsmost complex torm confined to it. Certainly on phylo-genetic grounds the argument cannot be upheld. Again, inby far the greater number of cases, atavism consists inretention of foetal characters, and the atavistic type is, asI have been so careful to point out, due to the retention offoetal characters which attain a functional condition. Ifduring its embryonic stages the human stomach presentedsuch a shape as that represented in Fig. 11, it could easily beunderstood that in some cases it would be permanent; butthis we know full well is not the case.Phylogeny and embryology are both eloquent in furnish-

ing denial on this subject; therefore it is illogical, and asunreasonable as it is anscientific, to regard this malformationof the stomach as a reversion. We must also be careful notto confound physiological types with reversions. Forexample: an erectile tumour is structurally similar to thecomb of a cock, yet no one would venture to suggest thatthe nsevi which occur so frequently in infants, immediatelyover the anterior fjntanelle, are to be regarded as reversionto a cock’s comb.A like instance is furnished by the submaxillary gland

of the armadillo. In this edentate, the duct, soon after itleaves the gland, dilates into a salivary bladder, serving as areservoir of some capacity. How easy it would be to say thatin cysts of the mouth produced by obstruction and subse-quent dilatation of the salivary ducts we have a goodinstance of reversion to the armadillo type. The thing at

So-called congenital contraction of the human stomach.

once strikes us as absurd. Take the case of those remark-able bodies found in some of the ganglia or cysts occasionallyconnected with the tendons of the flexors and extensors ofthe hand. Now bodies exactly resembling these occur con-stantly in connexion with the jaws of sharks. ProfessorCharles Stewart has shown that immediately above themandibular articulation in the skate there is a recess whereconcretions exactly resembling the melon-seed bodies areformed and passed down into the joint through a narrowopening. In this instance we may use these as physiologicaltypes of the melon-seed bodies found in ganglia, but thelatter must not be regarded as reversions. It must not beconcluded from this that I object to descend to fish to findreversions; on the contrary, the human body abounds in structures decidedly piscine-e.g., the enamel and dentine of teethand odontomata, and our primitive cartilaginous skele-ton ; in the possession of membrane, bones, branchial clefts,and the like. In these cases, however, we can trace themin mammals, thence to reptiles, downwards to amphibians,and ao on to fish ; but if a character appears in man which, Iso far as we know, occurs not in the intermediate forms, andespecially those closely allied, then objection must be takento it as being atavistic.

Let me now select an example which will serve to showhow much care is requisite in determining reversions. The

possession of lanugo by the feetus, which is as a rule shedin. utero, is a clear indication of a lost adult character merelypersisting in the embryo in obedience to heredity. Occa-sionally, however, the lanugo, instead of being shed, attainsfull development. This excessive growth may perhapsonly affect a patch half an inch square, but it may extendover half the body, as in Fig. 12. Such overgrowths areknown as moles. This is true atavism, for we have only todescend to man’s nearest neighbourq, the anthropomorphas,and the truth is evident. But every abnormal hairy patchis not due to overgrowth of lanugo. It has long be6n known,and Hunter was well aware of-it, that when parts have long

been irritated, us by the prolonged use ot poultices &c., an

abundant crop of hair baa been produced around the part.But there is a more subtle form of hairiness which leads tosome very remarkable speculations.There is a variety of spina bifid known as "occulta," the

chief peculiarity ot which consists m the non-existence of

Fia. 12.

A hairv mole on a man. It had become the seat of anepitlielioma. (From a drawing presented by Mr. GeorgeLawson to the Middlesex Hospital Museum.)

any external tumour, but a membranous spot may bedetected in the vertebral column, as described in the firstlecture. Associated with this is some thickening of themembranes, an accumulation of fat, or mixture of fat andstriped muscle fibre in relation with the spinal cord. Theirritation leads to the development of an abundant crop of

FIG. 13.

Abnormal hairiness of the loins, dne to the irritation of a spina bifidaocculta. (After Uecklinghausen.)

hairs, as shown roughly in Fig. 13, the hirslites being mostabundant in the vicinity of the detect. The case in questionwas reported by Recklinghausen,3 but it is not the mostperfect one that could have been selected, for a tumour hadbeen removed in early childhood from the patient. How-ever, it serves well to illustrate the point. -

3 Virchow’s Archiv, 1886.

407

Darwin4 draws attention to the curious variety of fowlswhich possess a topknot of feathers. as shown in Fig. 14,familiar to poultry breeders as the Polish fowl. The skullunderneath this tuft exhibits a remarkable deviation fromthe ordinary form seen in fowls. The deformity will bebest understood by a glance at the skull of a Polish fowl,shown in longitudinal section in Fig. 15. The summit ofthe protuberance in the Polish fowl often presents irregularmembranous spaces. Virchow regards the cranial deformityas of the nature of a hereditary encephalocele, and theluxurious overgrowth of feathers is associated with it, in the

FiG. 14.

Head of a Polish fowl with feathery tuft. (After Darwin.)

same way that excessive growth of hair is a concomitant ofspina bifid occulta in man, and even ordinary spina bifida.Polydactyly.-Supernumerary fingers and toes constitute

a class of malformations which give rise to great difficultyto those who have devoted attention to reversionaryphenomena. A very large number of cases of increase inthe number of digits has been recorded and carefullydescribed by teratologists, anatomists, and surgeons ; theextra digits varying from one or two phalanges, encased intissues, and hanging by a pedicle from a complete finger, oras a complete finger articulating with, or ankylosed to, a

FIG. 15.

Section of skull of the Polish fowl, showing the protuberance.

metacarpal or metatarsal bone. Darwin was of opinion thatsupernumerary digits are atavistic in the sense that theyare to be regarded as a process of budding similar to thatfound in the limbs of amphibians. This view, however, hasnot found favour. In order to find a vertebrate ancestorwith more than the typical number of five digits in manus

and pes, we should be obliged to descend to fish or suchsil reptiles as the ichthyosauri for types. From suchforms to man the gap is too enormous, and the modi-fications of the limbs so extensive that misinterpreta-tion is unavoidable. It has already been indicated thatwhen atavism occurs, although it may occasionally repro-

4 Animals and Plants under Domestication, vol. i., p. 262.5 Onkologie, Bd. iii., S. 274; and Archiv, Bd. ciii., S. 11, 1886,

Descendenz und Pathologie.

duce a remote ancestral character, it with far greaterfrequency represents those of its more recent ancestors.If all cases of supernumerary digits are reversions, whereare we to go for types with double hands, double feet, andso forth ? A broad survey shows that there is a tendency toreduplication in many parts of the body. Thus, in lizarde.reptiles, or amphibia double tails are not unknown; evenreduplication of the vertebral column occurs, not only inman, but in many vertebrates. Interesting examples of thebifurcation of the axis of a limb have been described byAlbrecht in the mud-fish, Protopterus annectans, and inCeratodus by Howes. A good example of the tendencyexhibited by digits to bifurcate is represented in Fig. 16. Itis the manus of a horse preserved in L’Ecole Veterinaire deLyons. In this case the phalanges attached to the main(third) metacarpal have bifurcated. If these are to beregarded as examples of atavism, we shall be obliged to findanimals with two tails, any number of spare digits, or evenlimbs. To insist that such examples are to be regarded asreversions is certainly inconsistent with sound reasoning.The following example will serve to show to what extent

care is necessary in deciding whether a given abnormalityis atavistic or otherwise. In the Teratological Collection ofthe Museum of the College of Surgeons is the interestingspecimen shown in Fig. 17. It consists of the skeleton ofthe right manus of a horse, with an additional largelydeveloped digit intercalated between the inner splint boneand the middle toe. The second row of carpal bones is pre-served, and exhibits an additional bone. The animal wasshod on both toes. A superficial glance at once suggeststhat we have here one of the horse’s lost digits reappearing.A critical examination reveals, however, that, if this is a caseof atavism, the splint bone on the inner side must represent

I FIG. 16. Fin. 17.

Bifurcation of the third digit of a A similar specimen. (Museum ofhorse. (After Chauveau.) Royal College of Surgeons.)

the thumb. This is contrary to what has been alreadyexpressed-viz., the parts last suppressed are those mostprone to reappear by reversion. If we take the painsto compare this specimen with Chauveau’s case representedbeside it, there remains very little doubt that it is notatavistic, but a reduplication of the middle digit-in fact,a malformation.In concluding these lectures, permit me to make the fol-

lowing remarks:-How many have felt, as the yearly totalof facts make their appearance in the volumes known asthe Transactions of the Pathological Society and Virchow’sArcltiv, that many wearisome details of the minutestructure of tumours and other morbid changes are recordedagain and again, until it seems that the description of thehistology of a diseased structure marks the finality of

pathological science. Pathology is sufficiently hamperedwith isolated facts already, and it is time that those whohave the energy and leisure should employ them in searchingfor some laws whereby to regulate this accumulation, whichbids fair to bring discredit on the pathologist. Comparativepathology, studied from the standpoint of evolution, offersevery inducement in this respect, and will yield a fruitfulharvest to those willing to toil in this fertile field.Note.-That part of the lecture devoted to " Branchial

Fissures and Supernumerary Auricles" appears in full in theJanuary number of the Journal of Anatomy and Physiology.The theory advanced to explain the transmission of male orfemale characters, and a full discussion of the morphologyof the prostate, will appear in the Proceedings of theZoological Society for December, 1886. The discussionregarding parasitic foetuses in the sacral region, with fullillustrations, will appear in the G1Inaecological Journal,vol. ii. The explanation of " meningocele" in the occipitalregion was published in Brain (October, 1886).

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