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

It is no part of the view here urged to deny that a single digit, like any other single member of a series, may divide into two (or even into three) for this phenomenon is not rare. Probably enough No. 559 is actually a case of such a division of the digit III. But here in digits as in mammae, teeth, &c., the evidence goes to shew t hat t here is no real distinction between the division of one member to form two, and that more fundamental reconstitutiou of the series seen in No. .~>57, for the state of No. 558 is almost halfway between them. In it we almost see the digit III in the act of losing its idem ity.

In dealing with these there are difficulties. The cases are examples of liniKs of < Salves or Sheep hearing four or live digits arranged in two groups cither of twu and two, or of two and three. The members of e,i< h group curve towards each other in such a way that each group lias a separate axis of Symmetry (Figs. 117 and US). In several such cases the two groups are related to each other as right and left. Of these facts two dill'erent views are possible. For first, a limb of this

kind may be a structure like the double-hands seen in Man (pp. 331 to •'!•'{ 7), for it is certain that an almost completely symmetrical series of puts is in those cases formed by proliferation of a series normally iieini -ymmetrieal, however unexpected this phenomenon may be. < Mi the other hand it might be argued that one of the groups of digits represents the normal, and that the other group is supernumerary. For, as will be hereafter shewn at length in the case of Insects, supernumerary appendages may grow out frx>rn a normal appendage and are then a pair, being formed as a right and a left, composing a separate Secondary Symmetry.

On the first view the digits of each group are in symmetry with each other like those of the normal limb, the two groups also balancing each other like the halves of a double-hand: on the other view one of the groups would be supposed to be made up of a right and a left digit III, or of a right and a left digit IV. The possibility of the second view being true arises of course in the Artiodactyles from the fact that in them the normal digits compose a bilateral Minor Symmetry.

There is nevertheless little doubt that the former account is the right one and that neither group is a Secondary Symmetry ; for were either of the groups really in Secondary Symmetry the supposed supernumerary group should contain at least parts of four digits. Lastly, some of the cases, as No. 566, are clearly of the nature of double limbs, both groups having a common axis of Symmetry. A further difficulty arises from the fact that most of these double limbs are old specimens cut off from the trunk. There is therefore no proof that such a limb is not that of a polynielian in Geoffroy St Hilaire's sense. In other words, though it is practically certain that neither of the groups of digits is itself a system of Secondary Symmetry it is quite possible, and in some cases likely that the whole limb is of this nature. In cases of duplicity, especially of posterior duplicity, the two limbs of one or both of the united bodies frequently form a compound structure somewhat resembling one of the double limbs here under consideration. Hence it is not possible to include with confidence great numbers of cases of double limbs described by various writers or preserved in museums, for it is rarely that particulars regarding the rest of the animal are to be had. This difficulty applies to almost all cases known to me and they are therefore given with this caution. This objection of course does not apply to such a case as No.

The following few cases will sufficiently illustrate the different forms of limbs included in this section. They consist of two chief kinds ; first, limbs like Nos. 563 and 566, in which both groups contain two digits, and secondly, cases like No. 567, in which one of the groups contains three digits, recalling the state described in the last section (cp. Nos. 558 and 559). Besides these there are some cases of amorphous extra digits not here related.

563. Cow, full-grown, right fore foot with four digits arranged in two groups of two, as shewn in fig. 116. The carpus not preserved. No particulars as to the rest of the animal. This specimen is in the Museum of Douai and is described in detail by DELPLANQUE, Etudes Teratologiques, n. Douai, 1869, p. 30, PL I. [The possibility that this may be a limb of a pygomelian is not excluded.] *564. Cenrus dama (Fallow Deer). A female having each hind foot double. The division occurs in the upper part of the tarsus, which gradually diverges into two separate tarsi [? metatarsi] and two separate feet. This doe had for several successive years dropped a fawn with the same malformation, though she had been served by several bucks. WARD, EDWIN, Proc. Zool. Soc., 1874, p. 90. 565. Two cases, a Roebuck and a Deer, mentioned by GEOFFROY ST HILAIRE (Hist, des Anom., I. p. 697) are probably of this nature.

FIG. 116. Specimen stated by Delplanque to have been the right foot of a Cow (see No. 563). (After *56G. Sheep, having four toes, each having three phalanges, on each p sterior limb (Fig. 117i. In each case the toes were arranged as two pairs, the hoofs of each pair being turned towardcadi other. Eucli foot had four united metatarsals, marked off from each other by grooves on the -nrface of the bone, the division between the metatarsals of each pair of toes being clearly marked at the peripheral • nds of the bones. In the case of each foot there were partof a pair of tai>i arranged in a symmetrical and complementary manner about the middle Hue of the limb. In cadi tar-us there was a large \> me having the structure of two calcanen, a right and a left, united poMeriorly ; the upward prolongation, proper to the calcaneum, was present on eiidi -id.' of this hour ;md projected upwards on each

of ill'1 til'ia. The astragalus of each foot was similarly a hone donlile in form, uniting in it-elf the parts of a ri^'ht and left a-tra^'alus. The left foot had a sin/le flat bone below tlie .-i-trau'alu-. ivpr. -< nting as it were two naviculars fused together ; and four bones in a di-tal row, representing pre-uinalily two ciiiioid-. and two cuneiform dements. In the rL'ht foot also there wa- a single bone below the LgalUB, and four other bon< - airan ;ed in a way slightly different from that of the other foot. EKCOI.ANI, ibid., p. 77:<. /'-('-. n. ligs. 7 and si.

[A case given by ERCOLANI (1. c., p. 783, Tav. n., figs. 9 and 10) of similar duplicity in a lamb seems to be very possibly a case of double monstrosity. In this animal the hind limbs were altogether absent.] Calf, having five digits on one manus. There is nothing to shew positively whether this specimen is a right or a left, and it is even possible that it is part of a polymelian1. Carpal bones gone. Metacarpals four, disposed in two pairs. One pair bear the digits <i4 and d5 (Fig. 110), which have a common proximal joint. Their ungual phalanges curve towards each other, forming a Minor Symmetry like those of a normal Calf. The other two metacarpals bear three digits ; two (d3 and rf2) articulate with one metacarpal having a divided epiphysis. The otheT metacarpal bears a digit (d1) of full size curving towards d'2. The ungual phalanges of d- and d3 are nearly straight [cp. Nos. 558 and 559.] C. S. M., Terat. Set:, No. 299.

Calf: left hind foot similar case : inner group of two toes curving towards each other and an outer group of three toes of which the middle one was almost bilaterally symmetrical while the hoofs of the other two were each turned towards it. Five metatarsals united but marked out clearly by grooves. Tarsus much as in No. 500. ERCOLANI, /. c., p. 774, Tav. i. fig. 8. Calf: left hind foot a somewhat different case, DEEW, Commercium Litterarium, Nuremberg, 1730, p. 225, Taf. in. fig. 2. [Description meagre, but figure good. Beginning from the iuside the five toes turned (1) outwards, (2) outwards, (3) inwards, (4) outwards, (5) inwards, respectively. There were only four metatarsals, (3) and (4) being both borne on one metatarsal.j

Of the great numbers of feet of polydactyle pigs recorded or preserved in museums all I believe are fore feet. No case of a polydactyle hind foot is known to me in the pig. All the cases are examples of proliferation upon the internal side of the digital series. With very few exceptions the variation takes one of two forms, consisting either in the presence of a single digit internal to the digit II, or in the presence of two digits. either separate or partially compounded, in this position. A very few cases depart from these conditions2. The condition is very usually the same or nearly the same in both fore feet.

570. Such a digit may either have a separate bone for its articulation in one or both rows of the carpus (as ERCOLANI, I. c., PI. I. fig. 3), or it may articulate with a half-separated extension of the trapezoid (as Coll. Surg. Mus., Ter. Ser., 297 A}, or with the metacarpal or other part of digit II (very common), sometimes simply branching from this digit without an articulation. In no case of which good accounts are to be 2 For example a 1. fore foot in which the metacarpal of II. bears a rudimentary digit on each side of the digit II, three in all. ERCOLANI, Mem. Ac. BoL, 1881. PI. I, fig- 1.

had does such ;i dL'it- ^roup itself into the Symmetry of the normal maiius : but it stands apart, or is bent or adducted behind the other diLrit-, having a ho. .f \vhidi is irregularly pyramidal, curving in neither direction especially. Such a digit has generally three phalanges, and is of about thf size of digit II, though not rarely it is large in size approaching more nearly to III than to II (as Coll. Surg. Jfus., Ter. Ser., L".'7>. .")71. This condit ion is not less common than the last. The two extra dibits art- Ix.rne cither by two separate extra carpal bones (Fig. 119, c1, c'), "i- by (tincarpal imperfectly divided (ERCOLANI, 1. c., PI. i., Jig. 6); or i lie metacarpals of the extra digits simply articulate against the carpn -metacar -pal joint of II (as in a specimen in my own possession). The extra dibits may be double throughout, or the two may be compounded in their proximal parts (ERCOLANI, 1. c., PL i., fig. 5; also case in < >xt'onl Mus.1, 150G, «, in which the two extra digits were ill-formed and of uiH-ijual size, having a common metacarpal). Fig. 119 shews Mich a pair of extra dibits in their most complete form. The central part of the metacarpal of II has either never ossified or has been absorbed. As bearing on the question of the relations of parts in MerUtic Hep, <t it ion tinfact of most importance is the circumstance that the digits III and IV retain their normal Symmetry, but the two

I. View from in front. II. View from inside to shew the convergence of <l} and i/- towards each other. (/', (/-, two extra digits placed internally, c1, ca, two extra carpal bones with \vhidi they articulate, sc, scaphoid. In, lunar, cit, cuneiform, t, trapezoid. in. magnum, n, unciforni. d3 — rf6, the digits II, III, IV, V. 1 For note of this specimen I am indebted to Mr W. H. Benham. extra digits form another Minor Symmetry of their own. It is perhaps worth noting that the metacarpal of the digit lettered d* in the form of its head is nearly the optical image of that of III (cZ4), but this resemblance may be misleading and must not be insisted on. Coll. Surg. Mua.t Ter. Ser., 298.

•572 Wild Boar. Two cases, apparently resembling the foregoing are described, from external examination only, in the wild boar by GEOFFKOY ST HILAIRE, Hist, des Anom., i. p. 696. This phenomenon is known in the Ox and is common in the Pig. In all cases the variation consists in a more or less complete union or absence of division between the digits III and IV. Among the many records of digital variation in the Pig no case relates to union between a lateral and a chief digit, but it is always the two chief digits III and IV that are united. (Compare the case of Man, p. 358.) In this case there is therefore an absence of a division in the middle plane of a bilateral Minor Symmetry, and the parts that remain united are related to each other as optical images. The phenomenon is thus the exact converse of the variation consisting in a division along a plane of bilateral symmetry which was seen in the Horses Nos. 547 and 550. As was remarked in speaking of similar variations in Man, it is to be noticed that if the union is incomplete, as it commonly is, the peripheral parts are the least divided, the division becoming more marked as the proximal parts are approached.

In the normal Sheep according to ROSENBERG1 the metacarpals II and V are distinct in the embryonic state, afterwards completely uniting with III and IV. The same is presumably true of the Ox ; but whether this be so or not, the digits II and V are in the normal adult not represented by separate bones in the hind foot, and in the fore foot V only is represented by the rudimentary * bone articulating with the unciform. Unusual interest therefore attaches to the observations made by BOAS and by KITT of the development of lateral metacarpals and metatarsals (II and V) in Calves having III and IV united. Note also that in two of Kitt's cases there was not only a development of lateral digits but also indications of a division occurring in them. Besides this, in the right fore foot of one solid-hoofed Pig (No. 585) there is a slight appearance of duplicity in the ungual phalanx of the lateral digit V.

On the other hand the reduction of accessory hoofs (ergots) in LANDOIS' case, No. 582, seems to be an example of a contrary phenomenon; for the connexion between the developed lateral metacarpals and metatarsals in Kitt's case (No. 579) must be taken as evidence that the accessory hoofs do really represent II and V. *573. Ox. Young o\ having tintwo dibits of the right fore foot completely united together. At the lower extremity of the large double metacarpal (111 and 1 V ) of the normal limb a deep cleft i> present, which separates the two articular extremities of the bone. In this specimen this deft was represented only by a sort of antero-posterior channel, at the bottom of which there was a slight groove, which was all that remained as an indication of the "M^mal double nature of the bone. At the back of this metacarpal there were only three so-amoids instead of four, and in the central one there was m.t the -lightest trace of duplicity. This sesamoid was placed opposite to the channel above mentioned. The two first phalanges wenentirely united, but the vestiges of this fusion could lie seen both before and behind and also in the two articular surfaces by which the bone was in contact with the metacarpal. The same was true of the second phalanges. The third phalanges however were so completely fused and so reduced in size that they had the appearance of a single bone. The two small sesamoids were similarly united. The general appearance of this limb was remarkably like that of the Horse. BARRIER, Rec. med, veter., IsM, Ser. 'i. Tome lo, p. 490. [No particulars given as to the condition of the other feet of the same animal.]

574. Ox having right fore foot with a single large metacarpal and one splint-bone I? V]. The peripheral end of the metacarpal had two articular surfaces closely compressed together, and these two surfaces bore but one digit of three phalanges and one hoof like that of a Foal. The preparation was an old one, and with regard to the accessory hoofs there was no indication that could be relied on. KITT, Dent. Ztschr. f. Tliierm., XII. 1886, Jaltrexb., L884— 53 p. (\'2, Case No. III.

575. Calf: each foot having only one hoof. The phalanges, sesamoids, metacarpals and metatarsals, wore all normal and the hoofs alone were united. The cavity nf the hoof was divided internally into two chambers, which were more distinct in front than behind. Externally each hoof was slightly bifid in front, but the soles of the t'tet were without trace of division. MOROT, C., Bull, de In Soc. ,1,' in-'il. n't., 1889, Ser. MI. T. vi. p. 39. Case I.

~>7ti. Calf: killed at 10 weeks old. The left fore foot alone was abnormal, having only "in hoof. Viewed from without, this hoof was like that of a young ass, but it bore a Blight HP ilian degression, which was about 3 cm. wide and only 1 to '2 mm. deep, which was all that remained to shew its double structure. Internally the cavity of the hoof was single, hut a horny ridge was present on the inside in the region ot the depression. The two unequal phalanges were peripherally united into a single bone, but. w. iv separate centrally, and the two parts were not quite symmetrical [details given]. The other parts were nearly normal. MOBOT, C., 7. c., Case 2.

*~>77. Ox. In a newly-born calf the following abnormalities were seen. Tn the right fore fn,,t thenwas a small well formed metacarpal bone on the outside of the normal paired metacarpals, and a similar but more rudimentary structure was also present on the inside of the limb. The additional outer metacarpal bore two small phalangeal cartilages, and with them had a length of about 10 cm.. but the supernumerary metacarpal on the inner side was more rudimentary and bore no trace of phalangeal structures. The toes

borne by the normal metacarpal of the right fore foot were abnormal, inasmuch as the second and third phalanges were united together. The first pair of phalanges were separate, but their outer ends were modified so as to articulate with the single second phalanx. The distal (third) phalanx bore a groove indicating its double origin, but the second phalanx was without any such groove, and was to all appearance a single structure. The left fore foot also bore an outer and an inner supernumerary metacarpal, but in this case it was the inner supernumerary metacarpal which attained the greatest size. This inner metacarpal bore two small phalangeal bones, while the outer extra metacarpal was more rudimentary and had no phalanges. The phalanges of the two normal toes were separate in the left foot, but though the bones were of the ordinary formation the two toes were enclosed in a common hoof. BOAS, J. E. V., Morph. Jahrb., 1890, p. 530,

BOAS also states that in the museum of the Agricultural School of Copenhagen are several instances of united toes in the fore foot of the Ox, and that in all these specimens the outer metacarpals (II and V) are larger than they are in normal specimens, but are not so much developed as in the case just described. BOAS, I.e. 578. A case [sc. Ox (?)] is also mentioned in which the two normal toes of the hind foot were united, and the median and distal parts of the metatarsals II and V were developed, though they are absent in the normal form. BOAS, I.e.

*579. Calf having the digits of each foot united and bearing a single hoof. The carpus and tarsus were not seen. Fore foot. The chief digits, III and IV, were completely united in the fore limbs and bore a single hoof, but, in addition to this variation, the metacarpals of the lateral digits, II and Y, were developed and ossified. The length of metacarpal II was 9 cm. and its thickness at the proximal end was 1-5 cm. Metacarpal V had a length of 8 cm. and a maximum thickness of 1 '3 cm. at the proximal end. The metacarpal of the united digits, III and IV, measured 13 cm. in length. The metacarpal V was slightly bind at its distal extremity, and here presented two articular surfaces. With the internal of these there articulated a bone measuring 2 cm. by 0'5 cm., and attached by fibrous tissue to the end of this bone there was a cartilaginous nodule. The external end of metacarpal V bore a rod-like piece of cartilage, 1 cm. in length. This and the cartilaginous nodule of the other part of the digit together formed the basis of one of the accessory hoofs (ergots), but the horny covering itself was divided by a deep cleft into two imperfectly separate parts. To the metacarpal of II was loosely articulated a bone 2-5 cm. in length, to which a nodule of cartilage was attached. The end of this digit was covered by an accessory hoof, which was imperfectly double like that of V and contained a second cartilaginous nodule, which was distinct from the first and was not supported by any proximal bone. The union between the digits III and IV was complete, and the reis. 25

suiting structure with its hoof was like that of the Horse. The articulationwere perfectly mobile. At the metacarpo-phalangeal joint there wentwo >e-;unoids only. [With this division in the lateral digit> on fa-ion of III and IV compare Pig, No. 585.] Jllii'l font. Tindigits III and IV were united as in the fore feet, but tin- -ingle hoof was more pointed. The metatarsals II and V wendeveloped. The latter was 12'7 cm. long, and was united to the lai-^e met;it;ir.-al above, but was free below, and was joined by a ligament to its accessory hoof. That of II began in the middle of the nietatai-Mis, being rart ilaginous and of about the thickness of a goosequill : it was coiineeteil with the accessory hoof by a ligament only. Km, Deut. Z.f. Thierm., xn., 1886, Jahresb. 1884-85, p. 59, Case

*580. Calf. Three of the feet had each one large digit (III and IV) formed much as in the last case. But in the dried preparation it could lie seen that in each of these feet there were four accessory hoot's, ;md connected with them several ossicles irregularly placed, representing phalanges 1 and 2 connected by ligaments with lateral metacarpals. The fourth foot [which?] had only three accessory hoofs, but the phalanges 1 and 2 of the digits III and IV were partially separated from each other, and there were two distal phalanges, one for e.-u-h digit ; but instead of being side by side, they were placed one behind the other, both being encased in a single hoof. KlTT, I.e., p. Gl, ( 'ase No. I I.

581. Calf. A right fore foot having the two chief digits (III and IV) represented by one digit with one hoof. The distal end of the common metaeai-pal had t \\ o urticular surfaces in close contact which bore a di-it iii \\hieh there were only slight traces of duplicity. The metacarpal of the digit V was represented by two small bones, one beside the upper and one beside the lower end of the large metacarpal. These two ossicles were connected together by a ligament which is prolonged downwards as far as the accessory hoof, and contains two nodules of cartilage. On the median side of the foot there is no rudiment of the metacarpal II, but the accessory hoof contains a nucleus of partly ossified cartilage. KITT, /. c., p. 63, Case IV.

'^'2. Calf having n single hoof on each fore foot. In external appearance, the hoof was a single structure, but its anterior portion shewed two projections which suggested that it was really a double structure. The outer accessory hoof was present on the right foot in a very much reduced form, but the corresponding structure of the inner side of the foot was entirely absent, and a marked ' turning-point ' in the hairs (//-/<;/<///•/„/) indicated the place where it should normally have been developed. In the left foot the accessory hoofs were in the same condition as in the right foot, but the ' turning-point ' was not formed at all. There were no skeletal structures corresponding to the accessory hoofs.

The skeleton of left fore foot was prepared. In it the metacarpal was 125 mm. long, having a deep cleft on its anterior face, indicating the line of union of the two mrtacarpals. The two articular heads, which in a normal animal of the same age are separated from each other \<\ about 5 mm., are in this specimen united by the inner edges of their anterior borders. The proximal phalanges formed a single bone, 32 mm. long. The division between the two bones was visible as a cleft on the anterior surface, in which place the two ossifications were distinctly separated from each other ; on the posterior surface the union between the two is continued for half the length. The second phalanges formed a typically single bone, as did also the distal phalanges which bore the hoof. The foramina for the two nutrient arteries of the two toes remained double and entered the single bone, one on each