Materials for the Study of Variation Treated with Especial Regard to Discontinuity in the Origin of Species

[A case perhaps similar to foregoing is briefly quoted by GRUBEE, 1. c., p. 471. note 83, as being in the 'Vienna Museum of Anatomy.] 512rt. Child: left metacarpal IV bore a supernumerary digit on external side. This digit was shorter than the digit IV and was completely webbed to it. BROCA, OiZu. Foetus (otherwise abnormal) : left hand bore extra digit attached by peduncle to first phalanx of digit IV. The minimus was separated from IV by a metacarpal space, standing almost at right angles to it. HENXIG, Sitzb. naturf. Ges. Leipzig, 1888. Oct. 9.

[AiiMON (Die angeb. Krankh. d. Mensch. p. 101, PL xxn. fig. 7) describes a case of rudimentary finger appended to the "ring-finger" and is so quoted by GRDBER; but the figure apparently represents the appendage as attached to the minimus.] (2) Duplication1 of single Diyits, especially of the Pollex and Hallux. *513. Duplication of the pollex or of the hallux is one of the commonest forms of polydactylisin and numerous cases have been described by all who have dealt with the subject. It consists in the development of two digits, complete or incomplete, in the position of the usually single series of bones composing the pollex (or hallux). In the section dealing with polydactylism associated with change of Symmetry (p. 326) we saw how upon the appearance of an extra digit in this position the thumb itself may have three phalanges. In these cases the extra digit may properly be considered as arising in Successive Series with the

1 A few cases are thought by some to shew triplication of digits, but it seems doubtful whether there is a case of division of one digit into three really equivalent digits, perhaps excepting the thumb of Xo. 521. . P.ut in a large majority of • -ases of the presence of an extra n tinradial side, the thumb has two phalanges as usual. Upon i review of the evidence it is I think clear that we shall In- right in considering th.-it iii mosl <>f these cases the extra digit is not really in Succession to the thumb, but that tintwo radial digits together rep re - -ent tinthiinili, tinincrease in number being achieved by duplication and not by siicces-ive addition.

.Must authors (GRUBEBj &c.) thus speak of these formations as ••double-thumb- and recognize them as examples of duplicity, but it -hould be remembered that tin- \ie\v of their nature is not consistent \\ith any statemenl that either of the t\vo digits is the extra one. If these thumb-' are instances »>f duplicity then both together represent t IK- normally single t liumb. In clear cases of double-thumb the two thumbs are equ'al or nearly eimal in si/.e and development, as commonly happens in cases of true duplicity. I>nuble-thumbs are known in every degree of completeness. The division between the two may occur at any point in their length. Thus the duplicity may be confined to the nail and first phalanx « ITTO, .!/«//>//•. sexc. 1><. "•'•/•(/>., Taf. xxv. tig. 1; BIKXKAUM, Monatsschr. i. f.'Jin /•/>•/.-., I860, xvi. p. Hi"); or it may include both first and second phalanges ((Jiiri'.KR, Arch. f. path. Anat. Phys., xxxn. 1865, p. 223); or both phalanges and the greater part of the metacarpal (GAILLARD, MI' in. Soc. de liol., 1^(31, p. 325); or even the whole digit and metacarpus, the two thumbs separately articulating with the trapezium f .losKi'ii, quoted by <ii;rBER, I.e., p. 463, Xote 37). It would be interesting to know which of these conditions is the most frequent, for it is likely that between the degrees of this variation there is Discontinuity, but the point is not easy to determine. As regards records the conditions first and last named are much the rarest, and the doublethumbs \\ith two sets of phalanges articulating with one metacarpal constitute the majority of cases.

Sometimes the two thumbs are webbed together (GRUBER, Bull. Ac. Sci. 1'i't. xv. p. 4SO, fig.) sometimes they are separate and may be YH-. 101. Hight hand having a thumb double from the metacarpus, shewing the relationship of images bot\\xrn the two thumbs. (After AXSAXDALE.) opposed to each other (FACKENHEIM, Jen. Zts., xxn. p. 358, fig. iv. ; AXNAXDALE, Diseases of Fingers and Toes, PI. in. tig. 25). This condition is important as an indication that between these double-thumbs there may be a relation of images (Fig. 101).

The duplicity may be and often is very different in degree in tintwo hands, though it is very commonly present in both. 514. The description given of duplicity in the pollex applies equally to the hallux, though of duplicity in the latter perhaps fewer cases are recorded. Here too the duplicity may be in all degrees of completeness. An example from ANNANDALE (I. c., PL in. fig. 32) is shewn in Fig. 102. FIG. 102. Feet of infant, No. 514, having thumb-like supernumerary digits arising from the metatarsi of the great toes.

Here a thumb-like extra hallux is borne on the inner side of the metatarsal I. Several such cases are known (cp. No. 517). 515. Among the cases called by authors "double-thumb" are a certain number in which the two thumbs are not equally developed, that on the radial side being more rudimentary. In such a case we are entitled to consider the radial thumb as an extra digit formed in Succession to the normal thumb, and not as a double of it. In speaking of other Meristic Series (especially mamnue and teeth) we have seen that it is not possible accurately to distinguish between cases of duplicity and cases of change in number of the series by formation of another member in the Succession. This is extremely well seen in digits. For firstly several conditions intermediate between the two are recorded by many authors (e.g. a case in which the radial thumb had two phalanges "ankylosed" together [or rather not completely segmented from each other]. GRUBEE, I.e., p. 480; cases in which the radial thumb had only one phalanx, ibid., p. 482; STRUTHERS, Edin. Neiv Phil. Jour., 1863 (-2), p. 87; BOULIAN, Kec. de Mem. de Jfed. milit., 1865, Ser. 3, xui. p. §l,fiys.}; and besides this there are several examples in which one hand bore a clear pair of double-thumbs, while in the other hand there is an extra radial digit in succession to the normal thumb (e.g.

FACKENHEIH, l,C.t p. 359, tig. iv.). Thus do the two conditions pass into each other, though some cases are clearly cases of duplicity ami some are clearly cases of extra digit in Succession1. I know no case of unruistakeable duplicity in any digit liut pollex or hallux ; but no doubt a good many cases of extra digit arising from the minimus may be of this nature (e.g. ANXANDALE, PI. in., fig. 28), though it is more likdy that the extra digit is in Succession.

In digits other than I or V the only case of possible duplicity known to me as occurring in a limb not exhibiting one of the complex conditions of polydactylism, are those of SlREXG ( Vierteljahrsschrij't f. ;//•<//,/. //<•///-.. \i. i \. 1 >">!), p. 178; original not seen by me; quoted by GKUBER, p. 47('i>, being a case apparently of double medius on one metacarpal : and of hrssKAC, Cut. Slus. Vrolik, No. 518, two terminal phalan-es on riirlit medius (together with double thumb; six fingers on left hand and peripheral duplicity of hallux in each foot). Accompanied by numerical Variation in other parts of the digital series such cases of duplicity are known in a few other cases.

Limbs not rarely present the forms of polydactylism already named in combination. Such combination may be found in the same limb, or one or more limbs may present one form, while another form may be found in the other limb or limbs. Of these combinations the following three cases will be sufficient illustration. Case of double hallux on each foot, and rudimentary digit attached /<// peduncle to tJie minium* of each hand. 516. A female member of a polydactyle family [particulars given] had an abortive supernumerary finger attached by a peduncle to the little finger of each hand. In the feet the two yreat toes were each partially double. In the left great toe the individual phalanges could be felt and there were two nails. In the great toe of tinright foot tin; adjacent sets of phalanges were inseparably united by their lateral borders, forming one bone, which was correspondingly broadened. There was only one nail which was notched in the middle of its free border. MUIR, J. S., Gla*;ioic .Mi'd. Jour., 18s 1, X. s. xxi. p. 4:20, Plate.

Case of each extremity with double pollex or haling and re dim'-ntu r>t digit attached to minimus. 517. Female infant having thumb of each hand double, the two sets of bones lyiug in the same skin and connective tissue. In the right hand the nails and phalanges of were quite distinct, but it was not certain whether the rnetacarpals \\en separate or not. In the left hand the nails \\vro not completely separate and the phalanges of the two thumbs were less distinctly separate. To the first phalanx of the little finger of each hand was appended a rudimentary bud-like finger, hanging by a peduncle.

The lent resembled the hands. From the inner border of the metatarsal of each great toe there proceeded a well-formed thumb-like toe with two phalanges. This toe was set at right angles to the great toe and could be tlexed and to some extent opposed. On the external border of the right foot there was a small extra little toe hanging by a peduncle from the metacarpal V. In the left foot the supernumerary little toe was bound up with the normal little toe for its whole length. HAGEXBACH, E., Jiiltrh.f. Kinderlieilk., xiv. 187'J, p. 234, //>-. [Cp. No. 514.]

1 Compare with thelargely similar series of phenomena seen in the foot of the Dorking fowl (r. ///mi). But in it if the two hallucal digits are not a true pair it is most commonly the /«//,•/• that is the largest, conversely, to the general rule in the extra digits arising from the pollex in Man. Case of double hallux in combination with extra digits on external side. 518. Man in Middlesex Hospital, 1834, having on the right foot two toes articulating with the first inetatarsal, and ou the left foot two toes articulating with the first metatarsal, and also two toes articulating with the fifth metatarsal. From the ulnar side of one of his hands two fingers had been removed. In each hand the middle and ring fingers were adherent throughout their length, as also were all the toes, except the minimi. Five brothers and three out of four sisters of this man had six toes on each foot and six fingers on each hand. The other sister had seven toes on one foot and six on the other, and had two extra fingers on each hand. London Jfed. Gaz., 1834, April, p. &5,Jigs.

Thus far we have considered cases of polydactylism that can be in some degree brought into order and included in general descriptions. There remain a small number of irregular cases each presenting special features which make general treatment inapplicable. These cases are instances of extremities, mostly feet, having seven, eight or nine digits. The descriptions of these cases are for the most part fragmentary, and as the bones have been examined in only one of them (MoEAND) so far as I am aware, the relations of the digits to each other and to the limb are obscure. Speaking generally in these irregular examples there is an appearance of division, possibly of duplication, of several digits. It should be noticed also that in some of them (e.g. BLASIUS, No. 520) the digits did not lie evenly in one plane but were in a manner bunched up so as to overlie each other. In such a case it would be interesting to know whether the digits originally grew in one plane and were afterwards shifted during growth, or whether the original Repetition was thus irregular.

As all these cases differ from each other an adequate account of them could only be given at great length, and by reproducing the original descriptions in full, together with such figures as are attainable. For these reasons it would not be profitable to introduce them here, though in a study of the nature of Meristic Repetition it is important to remember that these irregular cases exist. As illustrative of several cases I have appended an account of two complex cases in the foot and of one in the hand, giving references to such others as I am acquainted with.

519*. Girl, set. 6, having abnormal toes on the left foot as follows (Fig. 103). The total number of toes on the left foot was nine. From the position and form it appeared that the digits (6—9) representing II, III, IV and V were normal, but upon the radial side of these instead of a single hallux there were five toes. Of these 1 and 2 were imperfectly separated, articulating with the first metatarsal by their first phalanges, which were united to form a common proximal head. Each had a distinct second phalanx and in general form resembled a great toe having a separate nail. The second rnetacarpal bore firstly a pair of toes, 3 and 4, which were still less separate from each other than 1 and 2, the bifidity being confined to the soft parts. These two toes had one proximal and one distal phalanx in common. The second metatarsal also bore an external digit, 5, which in form rather resembled a normal third digit, being considerably shorter than 6 [and presumably containing three phalanges]. The toes 1, 2, 3 and 4 were found after amputation to be devoid of muscles and presented only the terminations of the flexor and extensor tendons

having their normal insertions. The toes 1 and 2 were supplied by the same flexor ten. lun which bifurcates and passes to be inserted into the ultimate phalanx ot each by a separate slip. The vinculum by which it is attached is common to the two bones. JOHNSON, ATHOL A., Trans. Path. Soc., ix. 1858, p. 4'27, jli. .")20. Maltinfant having supernumerary toes on the left foot. The tarsus and metatarsus were abnormally wide. The hallux appeared externally to be divided into two. This duplicity was most marked in the second phalanx and appeared in a slight infolding of the skin. The nail also shewed traces of duplicity. Next to the hallux were two toes which were bent upwards and inwards. Of these the one oveilay thu other. The uppermost was found after excision to have two sets of phalangeal bones enclosed in the same skin; these two articulated with a single metatarsal bone. The lower toe was thought by BLASIDS to represent the digit II. Next to this there was a rudimentary digit with a slightly developed nail. After excision it was found that this toe contained a cartilaginous basis which was partly segmented into two phalanges and articulated with a metatarsal. External to this rudimentary toe were three normal toes, representing as BLASICS supposes, the digits III, IV and V. Kxternal to the putative V was another digit of the same size and -liu]>r. DI.ASIUS, v. Siebolil'.t Jour. f. Gebiirtxh., xin. 1834, p. 131, figs. 1 and 2 ; figures copied in AHLFELD, Missb. d. Mensch., Taf. xx. fig. 11. [This foot appears to contain parts of ten digits.]

r»21. Child having polydactyle hands as follows. In each hand the fingers were webbed to the tips. < arh minimus having an extra nail. In the right hand the pollex was triplicate, having three sets of phalanges and three nails, the whole being in a common integument. In the left hand the pollex was duplicate, having two -ets of phalanges webbed together and two nails. Each member thus formed a prehensile paw. In right foot little toe webbed to next toe. Some (not all) of brotheis and sisters had similar hands: father and grandfather had similar hands: mother and grandmother normal. HARKKK, J., Lmu-i't, }*<'>'> \'2), p. HS'.t, ji;/.

;,•)•') The following are other examples of irregular polydactylism : MORAND, Mem. No. x. p. 474, supposes that this is a case of double-hand, palm to palm (as No. 503), but the original probably means that two adjacent thumbs arid two adjacent anuulares were united, the digits being all in one plane). ANNANDALE, Dis. of Fingers and Toes, 1865, p. 39 (eight metatarsals on a foot possibly associated with change of Symmetry). Ibid., p. 35, figs. 41 and 49 (pollex with two sets of phalanges but three nails, together with extra digit external to V). Cp. No. 521.

MELDE, R., Anat. Unters. eines Kindes mit beiders. Defekt d. Tibia u. Polyductylie an Hiniden it. Fiissen, Inaug. Diss., Marburg, 1892 (irnportaut). Though in reduction of digits the course of Variation is generally irregular and the result often largely amorphous there are still features in the evidence which may be of use to us, and a few selected cases are of some interest. These features will be spoken of under the three following heads, though for a general view of the subject reference must be made to teratological works.

As in certain cases of polydactylism it appeared that increase in the number of phalanges in the thumb could be regarded as a step in the direction of increase in the number of digits, so a reduction may be thought to be a step towards diminution in the number of digits. But though many cases of reduction in number of phalanges are recorded, there is in them nothing which suggests that they may be fitted into a series of gradual reduction comparable with the series of gradual increase already described. It is indeed chiefly as illustrating the possible completeness and perfection of Variation that these phenomena have a direct bearing on. the subject of Meristic Variation. The following case is chosen as being especially regular and symmetrical.

*523. ^au having only one phalanx in each hallux, and two in each of the other fingers and toes. The hands were almost exactly alike. The thumb had a short rnetacarpal f in. long, and one phalanx (1^ in.), the joint between them being loose as if composed of soft tissue. By the length of the rnetacarpal (Sin.) the index is longer than the other digits. The next two metacarpals have only half that length. The metacarpal of V is H in. long, but from its obliquity does not project so far as that of IV. The proximal phalanx of the index measures If, rnedius If, annularis 1, minimus 1£. The distal phalanx in index and middle |, ring and little f in. In left hand the distal phalanx of index is proportionally shorter. Except the index all the digits present their usual proportions. The feet are well formed as far as distal ends of metatarsals. The toes are short, pulpy and loosely articulated. Each has two phalanges except the hallux, which has only one. This case was a twin with a normal male. An elder brother and younger sister have the

As an example of similar and simultaneous Variation in both extremities this is an instructive case. Under this name have been described those cases in which two nr more digits are to a greater or less extent united together. In their In-.- 1 ring mi the morphology of Repeated Parts some of these \ariations are very instructive. It will be found that the important considerations in this evidence may be divided into two part-. ()f these the first concerns the manner of the variation and the 31 • "nd to the position in which it is most commonly found.

In many cases of union of digits the limb is amorphous; with these we have now no special concern. In simpler examples the digits may lie of normal form but some or all of them may be united by a \\rl) of integument for a part or the whole of their length. (For records of such cases see FORT, AXNAXDALE, <fcc.). *524. But besides these cases of webbing are many in which the union may be of a much more intimate character. Taking the cases together a progressive series may be arranged shewing every condition, beginning from an imperfect webbing together of the proximal phalanges to the state in which two digits are intimately united even in their bones, and perhaps even to the condition in which two digits are represented by a single digit (see No. 529). That the latter condition represents a phase in this series of variations does not seem to be generally recognized by those who have dealt with the subject but it is impossible to exclude it.

The lower conditions of this variation are sufficiently illustrated by Fig. 104, I and II (from AXXAXDALE, Diseases of Fingers and Toes, Jigs. 39 and :!.'>), shewing cases of medius and annularis partially combined for the whole of their length. A higher condition is shewn in Fig. 104, III, in which the same digits are united so closely that their external appearance suggests that only four digits are present in the hand. In this specimen (.\X\AXHALE, I. c., p. 14) there were nevertheless five metacarpals, but the first phalanges of III and IV were united peripherally and liore a M'eond and third ph;ilan\ and one nail common to them both. The same author (/. c. fig. 44) gives an illustration of such a set of bones from OTTO '.

Pithecia satanas (Monkey) : young male having the third and fourth digits of the hand on each Mcle completely connected by a fold of nude skin. The remaining digits of the hands and feet were normal. FOKI-.ES, W. A., P. Z. S., 1882, p. 1 1-.'. Macacus cynomologus : specimen having the fifth finger of the right hand represented by a rudiment only. On dissection the first phalanx of the fifth finger was found to be enclosed with that of the fourth. All the fingers of the abnormal (right) hand were somewhat misshapen and bore several exostoses. [? congenital variation] FRIEDLOWSKY, A.. V<>rh. zool. lot. Gen. Wicn, 1870. xx. p. 1017, 1'hitc.

1 I have failed to find the original of this figure in OTTO'S works. Before going further certain points are to be noted. First, the union as shewn in the figures is a union or compounding as of optical FIG. 104. Cases of syndactylism. I, II and III. A progressive series illustrating degrees in the union of medius and aunularis in the hand. IV. Case of union of index and medius of the foot. The union is incomplete peripherally. images in Bilateral Series, and is not like that of parts in Successive Series. Next, the union of the bones is more complete peripherally and less complete centrally. The latter is a rule very commonly observed in cases of the union of the bones of digits both in Man and other mammals. This statement is made without prejudice to the other fact that in the least state of syndactylism as manifested by union of the soft parts, it is the most central phalanges which are united. Such a case of partial union between II and III in the foot1 is shewn in Fig. 104, IV (AXXAXDALE, I. c., fig. 34). The rule that in the lowest condition of syndactylism of the bones it is commonly at the periphery that the union is most complete is also difficult to understand in connexion with

1 Compare several remarkable cases of this variation in one family, LE CLERC, Mem. soc. Linn. Normandie, ix. p. xxvi. the fact that the division of dibits in the lowest forms of polydactylism appears also first in tin- /»/•/////••/•«// phalanges. These phenomena appear to be in contradiction to each other. and I am not aware that the fact of tinappearance of the dibits early in the development of the liml> throws any light on the difficulty. The number of dibits wliich may be thus united is not limited to two, and exampleof intimate union between three and even four digitare common.

*527. Those who liave treated of this subject do not, so far as I ana aware, notice the fact that the phenomenon of Syndactylism most frequently affects part ii-ular dibits. From an examination of the recorded cases it appeai-s that in the hand there is a considerable preponderance of cases of union between the dibits III and IV. I regret that I have not material for a good analysis of the evidence on this point, but I may mention meanwhile that in a collection taken at random of some thirty-five cases of hands having only two digits united (chielly those gi\en by FORT and ANNANDALE) over 25 are cases of union of the digits III and IV ': in only one were the digits I and II united; the digit-* II and III in ? 4 cases ; the digits IV and V in ? 3 cases.

*52<S. On the other hand if two digits in the foot are united they are nearly always II and III. If in the hand thrw digits are joined they may be either III, IV and V, or (perhaps less commonly) II, III and IV. In cases of union of all the digits II to V, the digits III and IV are often much more intimately united than the others, and are often recorded as having a common nail, while II and V have separate nails. This question of the comparative frequency of the different forms of syndactylism would probably repay full investigation, and to the study of the mechanics of Division it would clearly be important. In the meantime may be noted the fact that the evidence suggests the possibility that we have here to do with a case of union of parts which are related to each other as optical images, and that the digits II to V of the hand constitute an imperfect Minor Symmetry within themselves. The fact that the subjects of most frequent union in the foot are the digits If and lil. not the digits III and IV as in the hand, may be e.nmeeted with the fact that the hallux stands to the foot in a different Lreometrical relation from th.-ii which tinpol]e\ bears to the hand and that consequently the axes of Symmetry are different in it.