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

54"). ' oal, in \\liich thr right anterior leg possessed two metacarpals and digits. The radius, ulna and proximal series of carpal bones were normal. In the • li-tal series only tico bones were present, viz.. an inner bone corresponding to the trapezoid. and a magnum. There was no separate bone corresponding to the unciform, but in its stead, the head of the outer metacarpal was continued upwards to articulate with the cuneiform. Between the heads of the two metacarpals was an irregularly quadrate bone which articulated with the magnum in the place where the large metacarpal (III) should be. This bone however only extended a little way, articulating at its outer end with a notch in the external metacarpal. [This is the author's view, but the figure strongly suggests that this quadrate bone may have been originally in connexion with the external metacarpal and that it may have been separated from it by fracture. If this were so, the large metacarpal would then not be represented by a separate bone at all.] The outer metacarpal distally bore three phalanges of irregular shape, flexed backwards and outwards. The inner metacarpal articulated solely with the trapezoid. Peripherally it bore a callosity which was due to the healing of a fracture. The phalanges of the inner metacarpal were three, but the first was reduced in length, while the second was elongated and bent in a sinuous manner. The ungual phalanx of this toe was cleft. [The author regards this case as analogous to the foregoing one, No. 544, that is to say, as an instance of development of the normally rudimentary lateral metacarpals to the exclusion of the large one (III), and he considers therefore that the large metacarpal (III) is only represented by the quadrate ossification which lay between the two developed metacarpals.] EECOLANI, G. B., Mem. della Ace. Sci. d. Istituto di Bologna, S. 4, T. in. 1881, p. 760, Tav. i.fiy. 11.

Foal in which the feet were all very abnormal. In the two fore feet the metacarpal of the normal toe (III) was very little developed, being however somewhat larger on the left side than it was on the right. It bore no digit. The external metacarpal bone (IV) of each fore foot attained a considerable length and bore a small hoof-bone. In the left fore foot the inner metacarpal was present but reduced ; in the right foot it was absent. Hit/lit hind foot also had the external metacarpal developed and bearing three small phalanges, but the central metacarpal (III) was fairly developed, bearing however only two phalanges. Left hind foot was amorphous. BOAS, J. E. V., Dent. Ztschr. f. Thiermedecin, vn. pp. 271 — 275. [For full description, measurements and figures see original.]

These cases are clear examples of the representation of a single digit by two. It will be seen besides that the two resulting digits may stand to each other in the relation of optical images (see Fig. 110) and do not form a Successive Series, thus following the common method of division of structures possessing the property of Bilateral Symmetry in some degree (cp. p. 77). All cases of this variation known to me occurred in the fore limb. These two hoofs are well formed and curve towards each other like those of Artiodactyles.

Mcp, peripheral end of metacarpal III. ext, external side, int , internal side. (After BOAS.) •549. Filly, two-year old, which had been born with left fore foot cleft like that of the Ox. Each of the two toes had three phalanges, which were completely separate as far up as the metacarpo-phalangeal joint. The division externally was carried to the same extent as in the Ox. The lower end of the great metacarpal III felt as if bifurcated like that of the Ox, so as to give separate articular support to the two toes.

I'pper parts normal. The lesser metacarpals, II and IV, felt through skin, seemed to terminate rather lower down in left foot than in right, but this was uncertain. Animal examined alive. No attempt at shoeing had been made, and hoofs having become elongated forwards had had their points sawn off. The whole foot was much larger or more spread than the other. STRUTHERS, J., Edin. New Phil. Jour., was normal as far as the distal end of the metatarsal, except for some

behind the upper part of the proximal phalanx. Two small sesamoids lay behind the third phalanx. A good deal of exostosis had taken place in all the phalangeal bones. ARLOING, M. S., Ann. Sci. Nat., Ser. V., Tome vin. pp. G7— 69, I'l. Foal : in right fore foot the large metacarpal divided into two parts, each bearing a separate digit. The proximal row of the carpus consisted of four normal bones, but the distal row was composed of two bones only. The external splint-bone (IV) was of normal proportions, but the internal splint-bone (III had almost completely disappeared. The large metacarpal (III) divided in its peripheral third into t\\o equal cylindrical branches, each of which bore a digit composed of three phalanges and bearing a crescentic hoof. These two digits were bent across each other in a shapeless way. DELPLANQCE, Mem. Soc. ccntr. </'.-)///•/<-. <lii I >'']>. <lit 'Nord, a. 2, ix. Douai, 1866— ls(57, p. '•_».»:.,

Mule, having two distinct toes on each fore foot. The hoofs were shaped like those of the Ox. They were of unequal length. JOLY, (.'<»n}>t,'x Kaulng. 1860, p. 1137. [Perhaps a case belonging to this section.] sc, scaphoid, tp, trapezoid. II, III, IV, metacarpals. 111(7, III b, internal and external sets of phalanges representing the digit III of the normal. We have now seen cases of increase in number of digits occurring by addition to the series, and cases occurring by division of III. It may at first sight seem impossible that there can be any process intermediate between these two. Nevertheless the word sufficiently nearly describes the condition of at least the first of the following cases, and is to some extent applicable to the second also. If the condition shewn in Fig. 1 1 2 be compared with those in Figs. 106 and 110 it will be seen that it is really intermediate between them.

*553. Horse (young): right manus with internal supernumerary digit. The bones are not in place, but have been attached with wires. The condition is as follows. The distal series of carpus remains and is normal or nearly so. Of the splint-bones, the inner (mcp. II) is thicker than the outer mcp. IV, but it is very little longer. The large metacarpal (III) is almost, but not quite, bilaterally symmetrical about its middle line. In the distal epiphysis the asymmetry is distinct, the internal side of the epiphysis being less developed than the external side. This epiphysis bears a large digit of three phalanges, but instead of being bilaterally symmetrical, like the normal toe of the Horse, each of the joints is flattened on the internal side, the flattening increasing from the first to the third phalanx. The hoof is greatly flattened on its inner face.

Internally to the epiphysis of the digit III there is a separate small bone, representing the distal end of an inner metacarpal. This bone bears a digit with two phalanges, and a hoof which is flat on the side turned towards the other hoof, like that of a calf, though it only reaches to the top of the larger hoof. The first phalanx of this digit is imperfectly divided by a suture into two parts. This division is not that of the epiphysis from the shaft. This extra digit may be thought to be that of mcp. II, but it is clear that it was in part applied to mcp. III. Note also that mcp. Ill is modified in correlation with its presence. Coll. Surg. Mas., in Terat. Cat., No. 301. man

The foregoing case well illustrates the made- NO. 553, from behind, quacy of the view on which an individuality is m, magnum, td, tra- The smaller digit in it is as regards the Symin Coll. Surg. Mus.). rnetry of the limb complementary to the larger digit. It is a partial substitute fur the inner half of the digit III. If the visible Symmetry of the limb is an index of mechanical relations in which the parts stood to each other in the original division of the manus into digits it is possible that there may have been a mechanical equivalence between the two digits.

554. Mule (between jackass and mare): foetus of about nine months having supernumerary digits. Hind limbs normal. Fore limbs normal as far as peripheral ( mlof metaearpals. Each manus consisted of three digits. Iii<iht. Metacarpale II and IV normal splint-bom >. .Me tacarpal III normal as far as line of union with its di-tal epiphysis. The inner part of the sheath of the epiphypis is continued into a rod of fibro-cartilage which supports an extra toe. This rod of cartilage contains a small ossification \\hirh lepresent*, as it were, the proximal phalanx of this internal supernumerary toe. Its outer end bears a small second phalanx, and this bears a small distal phalanx which was covered by a hoof. This extra toe, therefore, is internal to the main continuation of the leg, commences from the line of union . een the large metacarpal and its epiphysis, and has three phalangeal joints. The epipbysis of the large metacarpal supports a normal first phalanx with which the second phalanx articulates. This second phalanx is enlarged internally [details obscure] to bear a small extra nodule of cartilage which appears to be of the nature of an extra toe. The second phalanx al.-o I*, at- a large third (ungual) phalanx. This ungual phalanx together with the minute supernumerary toe borne by the second phalanx are together encased in a common hoof, but the hoof is divided by a groove into two distinct lobes, corresponding with the division between the two digits which it contains. The whole foot, therefore, has one free internal toe and one large toe bearing a small internal one, which are enclosed in a common hoof.

Left fore foot. Fig. 113. The small, lateral metatarsal II and IV, and the large central metatarsal III are normally constructed ; but from the inner side of the sheath of the large metatarsal, upon the line of union between the bone and its epiphysis, arises a fibre-cartilaginous rod, which contains an ossification representing the proximal phalanx of a supernumerary toe (lettered II in fig.). This rod of tissue in its proximal portion is represented in the figure as abutting on, but distinct from the end of the inner small, !ati i al metatarsal. It bears a cartilaginous second phalanx, containing a small ossification, which articulates with a terminal i ungual) phalanx covered by a hoof.

The distal end of the large metatarsal articulates with a large first phalanx, which at its proximal end is of normal width. At about its middle point this phalanx bifun-at. - into two parts, of which the inner, Ilia, is short and ends a little beyond the point of bifurcation : it bears an nniinnl phalanx only, which is encased in a hoof. The outer limb (III b) of the bifurcated first phalanx bears an elongated second phalanx of somewhat irregular shape which carries a larger ungual phalanx covered by a separate hoof. In this foot, therefore, there is an inner toe consisting of three phalanges attached to the inside of the large metatarsal : next,

the proximal phalanx of the large toe is divided longitudinally into two parts, bearing (1) an internal toe having only the ungual phalanx and hoof; (2) an outer toe which has a second and third (ungual) phalanx. In the case of both feet, the hoof and uugual phalanx of the outer toe are turned inward*, having an external curved edge and an internal straight edge; but the two inner toes in each case are turned ontinirdx, having their outer edges straight and their inner edges curved. JOLY, A. et LAVOCAT, N., Mem. de I' Ac. de* .So/, de Toulouse, S. 4, Tome in., 1853, p. 364, Platen. [Authors regard this case as proof of

IV, the external splint-bone. Ill, the chief metacarpal. Ill'/, III/;, internal and external rudimentary digits borne by III. II, a supernumerary digit attached to the inner side of III. truth of certain views of the phytogeny of the Horse and employ a system of nomenclature based on these views. This is not retained in the abstract here given.] In the domesticated animals of this order digital Variation is not rare, being in the case of the Pig especially common. Such variation has been seen in the Roebuck and Fallow Deer, but not in any more truly wild form so far as I am aware. These variations may take the form either of polydactylism or of syndactylism. Of the former a few cases are known in Ox, Sheep, Roebuck Fallow Deer, and many cases in the Pig ; syndactylism has been seen only in the Ox and in the Pig. The absence of cases of syndactylism in the Sheep is a curious instance of the caprice with which Variation occurs.

The phenomena of polydactylism in Pecora may conveniently be taken separately from the similar phenomena in Pigs. At the outset one negative feature in the evidence calls for notice. It is known that in the embryo Sheep rudiments of metacarpals II and V exist l which afterwards unite with III and IV. In view of this fact it might be expected by some that there would be found cases of Sheep and perhaps Oxen polydactyle by development of the digits II or V. In the Sheep only one case (No. 555) is known that can be possibly so interpreted; and in the Ox there is no such case unless Nos. 557, 558, and 559 should be held by any to be examples of the development of II, a view attended by many difficulties.

The two following examples are the only ones known to me in which there can be any question of reappearance of a lost digit, but in neither is the evidence at all clear. *555. Sheep. Some specimens of a small Chilian breed had an extra digit on the hind foot. It was not present in all individuals and was not seen to be inherited; but normal parents were observed to have offspring thus varying. [From the description given I cannot tell whether the extra digit was internal or external. Also, though said to have been on the hind foot, in describing the bones the cannon-bone is twice called metacarpus ; probably this is a slip for metatarsus.] The digit was only attached by skin. It contained a bent bone, of which^ the upper segment was 20 mm. long, the lower 13 mm. Proximally the

cartilaginous head of this bone rested in a pit on the tendon of the flexor brevis digitorum at the level of the end of first third of the cannon-bone, and peripherally it bore an end-phalanx and daw-like hunt', properly articulating. Xo splint-bones present. [Other details given : it was suggested that the bent bone represented an extra ' metacarpal ' and first and second phalanx.] VON NATIM-SITS, H., Die Srlmf:uclit, 1S80, p. 143. 556. Capreolus caprea (Roebuck), 2 yr. old, killed in district of Betzenstein, having a slender fifth digit on the inside of each fore foot. In the left there was a small, conical metacarpal element, bearing a digit with three phalanges. The right extra digit had a longer metacarpal piece with epiphysis, but in it there were only two phalanges. Each bore a hoof of about the size of those of II or V. The hoofs curved outwards. BAU- MULLER, C., Abh. naturh. Ges. Numb., ix. 1892, p. 53, PL

Other cases of polydactyle Pecora mostly fall into two groups : (1) Examples of limbs having three digits borne by a large cannon-bone made up of three metatarsal or metacarpal elements, grouped in one system of Symmetry. The axis of Symmetry is then deflected from the normal position, and instead of falling between two digits it approaches more or less to the central line of the middle of the three digits. The degree to which this change of Symmetry takes place corresponds irregularly with the extent to which the innermost digit is developed. This form is known in the Ox only [? Goat].

(2) Limbs in which the series of digits has two more or less definite axes of Minor Symmetry. Both of the systems of Svmmetry thus funned are in addition arranged about one common axis of Symmetry. The nature of this condition will be discussed later. It occurs in Ox, Sheep, Roebuck and Deer. 55 1. Calf. Right manus (Fig. 114) having three digits borne by a single cannon-bone. This is an old specimen of unknown history which was kindly sent to me by Mr \T. L. Sclater for examination.

Of the carpal bones only the distal row remains, containing a trapezoido-magnum and unciform nut differing visibly from the normal. The cannon-bone spreads at about its middle into three sub-equal parts, each ending in a separate articular head bearing a trochlear ridge. Between these articular surfaces the only point of difference was that in that of the middle digit (b), the trochlear ridge was rather nearer to the outer surface of the joint, not dividing it into two halves as usual (see figure). The foramen for entrance of the nutrient vessel was in the channel between the external and middle digits. This channel was very slightly deeper than the corresponding channel between the middle and inner digits. Each articular head bore a digit, well formed,

of approximately similar lengths, having a hoof. The hoofs of the outer and inner digits curved to the middle line of the limb, like the tpM. trapezoido-ruaguum. unc, unciform. n. for., nutrient foramen. V, dotted outline shewing position of supposed rudiment of digit V. Sesamoids not shewn. normal hoofs of a cloven-footed animal, but the hoof of the central toe was convex on both sides. The two accessory hoofs were in place, one on each side as shewn in the figure. The whole manus was very nearly symmetrical about the middle line of this digit. It was noticeable that the outer and inner hoofs were both rather narrow in proportion to the length of the limb, but the whole width of the foot was rather greater than it should be. The small bone considered to represent the digit V articulates with the unciform as usual, being of normal size. Each of the three digits was supplied with flexor and extensor tendons.

558. Heifer having three fully developed toes on each hind limb. The right hind foot described (Fig. 115). The calcaneum, astragalus and cuboido-navicular presented no special abnormality. The cuneiform ••i-ies usually consisting of two pieces in the Ox, were here represented by one piece (c and c8), though externally the bone seemed to be in two pieces. The internal portion (<•) approximately corresponding in position with the normal ento-cuneiform was imperfectly and irregularly divided by a groove into two parts. The metatarsus or cannon-bone at its proximal md was almost normal, but from about its middle it ^pread out into three parts as shewn in the figure, each part ending in an articular surface and bearing a digit, but the trochlear ridge for the innermost digit (ac) was not quite so large as those for the others. From the skeleton it seems clear that this innermost digit could not have readied the ground.

Of the three hoofs the middle one was the largest, the other two being nearly equal to each other in size. The outermost hoof curved inwards and the innermost hoof curved outwards. The middle hoof also curved outwards, but less so tlian tlmt of a normal </i</it ///, being rather flutter underneath, and having its two edges more nearly symmetrical. The accessory hoofs ('ergots' of French writers) were " in their usual place, on either side of and behind the foot." This specimen was originally described by GOODMAN, NE- VILLE, Jour. Anat. Phys., 1868, Ser. 2. i. p. 109.

arose, of which about ten generations were produced. The three-toed condition appeared in ally resembling the last case. The external diint is nearly normal. The middle digit is very thick, and is somewhat twisted and llexed. Its lingual phalanx is not specially curved in either direction but it is not truly symmetrical. The innermost di'_rit is thin and short and its ungual phalanx is not much curved. In this specimen there is a A*, astragalus. c/c, calcaneum. c, c-3, parts of a large united bone representing cuneiforms.

Ill, IV, (I--, letters affixed to illustrate the hypothesis that III and IV represent decided appearance of division in the distal epi- n()rmal> ;md that HC phvsis of the metacarpal of the middle diLMt ;s ;ui accessory digit. The following two cases are perhaps of the same nature as the foregoing. 560. Goat having three digits in each manus, described by GEOFFROY Sx HILAIRE, Hint, de A Anom. i. p. 689. The description states that a supernumerary toe was placed between the two normal toes. The middle toe was one-third of the size of a normal toe, but the lower part of the foot was larger than usual. This case was probably like No. 557 ; for from the shapes of the lateral hoofs that case also might seem to an observer at first sight to be an example of a toe "intercalated " between two normal toes. But in No. 5GO the middle digit was reduced.

•561. Calf having a small supernumerary toe 'placed between the digits of the right manus.' This toe had a hoof and seemed externally to be perfect, but on dissection it was found to contain no ossification, but was entirely composed of fibrous tissue and fat. ERCOLANI, Mem. Ac. Bologna, S. -1, in. p. 772. [Probably case like last, the middle digit being still less developed.] 562. Calf: right fore foot having three complete metacarpals, each bearing a digit of three phalanges. The two outer were disposed as in the normal, but the innermost rnetacarpal was quite free from the others and its digit stood off from the others [not grouping into their symmetry as in preceding cases] and having an ungual phalaux [of ? pyramidal shape]. DELPLANQUE, Etudes TeratoL, Douai, 1869, n. p. 33, PI. II. Jigs. 2 and 3. [It is difficult to determine the relation of this case to the others and I am not sure that I have rightly understood the form of the inner digit ; but since this digit seems to be outside the Minor Symmetry of the limb it is almost impossible to suppose that it can really be the digit II reappearing. I incline to think that it is more likely that this digit belongs to a separate Minor Symmetry. Compare the similar phenomena in Pigs, No. 570.]

On the foregoing cases some comment may be made. It may be noted that the two first (Nos. 557 and 558) present two stages or conditions of one variation. In No. 557 all three digits reach the ground and the change of Symmetry is completed ; in No. 558 the internal digit is not so large in proportion and the plane of Symmetry is not deflected so far. As to the morphology of the three digits in these cases three views are open on the accepted hypotheses. First, the internal digit (if it be admitted to be the supernumerary) may be simply a developed II. The existence of the normal accessory hoofs practically negatives this suggestion, for there can be little doubt that one of them represents II (v. infra, No. 579). The condition of the cuneiforms in No. 558 suggests further that an element is introduced into the cuneiform series between the almost normally formed ento-cuneiform and the ecto-cuneiform. But if this new element is the middle cuneiform, then the internal digit (Fig. 115, ac) may still be II. But the innermost ergot is II in the normal. Or is the inner ergot in this case I, and is this once more a case of the development of a normally terminal member, II, and of the addition of I beyond it in correlation, as we saw in the Horse (see p. 364) ? That such a correlation may exist is unquestionable, and it is not clear that these cases are not examples of it. But even if this principle be adopted here as a means of bringing these cases into harmony with received conceptions it will presently be seen that it still will not reconcile some other cases, notably those of the presence of supernumerary digits in a Minor Symmetry apart from that of the normal series. Yet if the conception of the digits as

endowed with individuality be not of universal application, we shall IP .1 save ii even it' bv ingenuity we may represent the facts of the piv-,.iit case a- in couf. trinity with its conditions. On the other hand it maybe suggested that there is a division of sunnone dn;it, and undoubtedly in No. 559 there is a suggestion that the innermost digit and the central digit are both formed l>v division .,f III. Jiut in the first place this view cannot so easily biextended to NOB. ">.~>7 and 558, for in them there is practically no indication that the dibits are not all independent and equivalent. The circumstance that the nutrient vessel enters between the external and middle digits may perhaps be taken to shew that they are 111 and IV; but this vessel, if single, must necessarily enter in dminother of the interspaces and there is no reason for supposing that, were there an actual repetition of a digit, the vessel must also be doubled, though doubtless repetition of vessels commonly enough occurs with repetition of the organs supplied.

Next, the Symmetry of the foot, the development of the middle digit bo take a median place, the position of the accessory hoofs, one on either side equidistant from the middle line of the manus, all these are suivlv indications that this limb was from the first developed and planned as a series of three digits, and not as a series of fir*, digits of which one afterwards divided. The series has a new number of members, and each member is in correlation with the existence of the new number remodelled.