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

Pig. " Solid-hoofed " pigs have been mentioned by many writers from the time of ARISTOTLE. The fact that they have been reported as occurring in many parts of the world makes it likely that the variation has often arisen afresh. The first case (No. 583) is the only instance of complete union of III and IV in the pig that is known to me. The variation is most commonly simultaneous in fore and hind feet. As seen, it occurs in many degrees. Several specimens not separately mentioned below are in the Coll. Surg. Mus. and other collections.

A fore foot and a hind foot of the same individual, in which the two chief digits were completely united, viz. represented by a single series of bones. In each case the two chief metacarpals and metatarsals (III and IV) were respectively represented by a single large bone, and with each a single digit of three phalanges articulated. The bones of these digits were straight, and not curved as they are in an ordinary foot in which two toes are present. There was not the slightest trace of duplicity, and the lateral digits were placed symmetrically on either side. The sesamoids were two in number

FIG. 120. Bones of feet of solid-hoofed Pig, No. 583, from specimens in the Museum at Alfort, described by BARRIER. The numbers II and V indicate the digits so numbered in the normal. instead of four. The carpus and tarsus appear to have also been changed in connexion with this unification of the digits, for in the distal scries at len-t tinnormal number of bones was not present. [The i'cct had licdi cut off across the tarsus and carpus before being received. By kind permission of the authorities at Alfort I > xamiiied these specimen- and made the sketches in Fig. 118. I could not satisfactorily identify the bones of carpus and tarsus. The proximal parK were ro \ered by a large exostosis.] The extensor of the phalanges ended iu three tendons only, and the same \\as true of the deep and superficial flexors. The central tend. .a in each case however shewed signs of its double nature. BARRIER, Rec. med. ve'ter., 1884, Ser. 6, Tom. xm. p. 491.

• >-s>4' A -keleton of a solid-hoofed pig exists in the Museum of the Royal College of Surgeons of Edinburgh which was presented by Sir Neil .Meuzies of Rannoch, Perthshire. Inquiries instituted by Struthers ( 1 >!'.."> j elicited the following facts. " The solid-hoofed pig has been well known and abundant on the '•-tates of Sir Neil Menzies at Rannoch for the last forty years. Most, if not all of them, were black. They were smaller than the ordinary swine, and seem to have had shorter ears. They liked the same food and pasture as the common swine, and showed no antipathy to herd with them. They were more easily fattened, though they did not attain so large a size as the ordinary swine ; their flesh was more sweet and tender, but some of the Highlanders had a prejudice against eating the flesh of pigs which did not "divide the hoof," unaware apparently that the Mosaic prohibition applied to all pigs. A male and female of the solid-hoofed kind was brought to Rannoch forty years ago, by the late Sir Neil Menzies, which was the commencement of the breed there ; but I have not been able to learn where they were brought from. Although they did not breed faster than the common kind, they multiplied rapidly, in consequence of being preserved, so that the flock increased to several hundred.

"At first, care was taken to keep them separate, on purpose to make them breed with each other, but after they became numerous they herded promiscuously with the common swine. As might be expected in a promiscuous flock, some of the young pigs had solid and some cloven feet, but I am unable as yet to say whether any definite result was ascertained as to the effect of crossing; whether any experiments were tried as to crossing; or whether after the promiscuous herding, some of the pigs of the same brood presented cloven and some solid hoofs.

"No pig was ever known there with some of its feet solid and some cloven ; nor, so far as is known, was there any instance of young born with cloven feet, when both parents were known to be solidhoofed. The numbers diminished— for what cause is not apparent; so that last year there was only one or two — one of them a boar, \\liich died ; and now the solid-hoofed breed appears to be extinct in Rannoch." .Vs."). "/•'<»•<' foot. — The distal phalanges of the two greater toes are represented by one great ungual phalanx, resembling that of the Horse,

but longer in proportion to its breadth. The middle phalanges are also represented by one bone in the lower two-thirds of their length, presenting separate upper ends for articulation with the proximal phalanges. The proximal phalanges are separate through their entire length. The whole foot above the middle phalanges presents the usual arrangement and proportions in the hog." Middle Phalanges. " There is no symphysis or mark indicating a line of coalescence of the two phalanges. The surface across the middle is somewhat irregularly filled up to nearly the level of each lateral part. Each half of the phalanx, as indicated by the notch between, the separate upper ends, has the full breadth of the proximal phalanx above it." Distal Phalanx. The middle part of this is raised above the lateral parts, and is partially separated from them by a fissure on each side, giving it an appearance as of the union of three bones. The end of the phalanx is notched like that of the horse ; it bears no trace of symphysis. ' ' The ungual phalanx of one of the lesser internal toes of the fore foot presents a bifurcation reaching half the length of the phalanx." See Fig. 121.

FIG. 121. I. A right fore foot of a solid-hoofed Pig, No. 585, from in front. The ungual phalanx of the digit V is bifid [cp. Nos. 579 and 580]. II. Middle digits of foot of solid-hoofed Pig, No. 587. x, an extra ossification wedged in between the phalanges of III and IV. (After ELLIOTT COUES.) " Hind foot. In the hind foot only the distal phalanx is single — There is no trace of double origin to the bone." STRUTHERS, J., Edinburgh New Phil. Journ., 1863, pp. 273-272, Jigs.

A pair of solid-hoofed pigs received by Zoological Society of London from Cuba in 1876. The sow gave birth to a litter of six [the solid-hoofed boar being presumably the father]. The six young were three males and three females. The hoofs were solid like those of the parents in two males and one female : in the others the hoofs were cloven as in the normal pig. The feet of one of the solid-hoofed males of this litter were dissected, and it was found that " the proximal and second phalanges are separated as usual, whilst at the extreme distal ends of the ungual phalanges

these bones are completely fused together ; and, further, a third ossicle was developed at their proximal ends, where they are not completely united, between and above them " [cp. No. ;>"]. " It might have been imagined that the deformity was simply tinresult of an agglutination alnur tin middle line of the two completely-formed dibits ; but such is not the case, the nail-structure being absent in the interval, win ir it i- replaced by bone with a transverse cartilage below it. The nail is continued straight across the middle line of the hoof, as in the horse." GAKKOD, A. H., I •. y.,,,,1. 8oe., 1877, p. 83.

")S~. J'uinestic pigs having the two central hoofs compounded into a single solid hoof have been kuown to occur several times in America. The two other toes remain di-tinct in the.-e cases. A breed of pigs having this character is said to have been ..li>he.l in Texas, which transmits this peculiarity in a definite way. In this breed the peculiarity is said to have been so firmly established that "no tendency to revert to the original and normal form is observable in these pigs." A cross between a solid-hoofed boar and an ordinary sow is said to produce a litter of which the majority shew the peculiarity of the male parent. " On the sole of the hoof, there is a broad, angular ele\ati<m of horny substance, apex forward, and sides running backward and outward to the lateral borders of the hoof, the whole structure being curiously like the frog of the horse's hoof. In fact it is a frog, though broad, tlatteued, and somewhat horseshoe-shaped, instead of being narrow, deep and acute as in the actual frog of the horse. This arcuate thickening of the corneous substance occupies about the middle third of the whole plantar surface of the foot." Tinterminal phalanges are united together, and above this single bone is another independent ossification lying between the second phalanges of the two digits, which remain distinct. [Cp. No. 586.] COUES, ELLIOTT, Bull. U. S. Geol. Geogr. Surv., iv. p. 2'.i.~., fig.

,",ss. Case resembling the above reported from Sioux City, Iowa, in which these pigs ' were bred for some time and were advertised for sale, with the statement that they were also of superior quality. Other cases given from different parts of the United States. In one of these it is stated that one hind foot was thus formed [the others 589. PlS- In all four feet the digits III and IV partially united and covered by one hoof. The metacarpals and first phalanges were separate in each case but the second and third phalanges of the two digits were united together. The common hoofs were not compressed laterally, as. in some of the cases seen in the Calf, and the .small digits II and V were unmodified. KITT, Dent. Zt. f. Thierm., xn. 188(5, Jahresb., 1884-85, p. 64, Case IV, Jigs.

The whole number of cases of Polydactylism recorded in birds generally is small. The phenomena however seen in the Dorking fowl arc well worthy of attention and have scarcely been adi •< | iini i -ly treated. I propose here to give an account of this case, mentioning instances seen in other birds and indicating so far as may be their relation to the facts of the Dorking. Five-toed fowls have been known from very early times. The character is now most definitely associated with the Dorking, though it is also considered necessary in Houclans for show purposes. It is likely that the latter breed derived the fifth toe from the Dorking. Fifth toes may often be seen to occur in other breeds, but I cannot quote a satisfactory record of their appearance in pure strains.

In the foot of an ordinary four-toed fowl the hallux articulates with the tarso-nietatarsus by a separate metatarsal. The hallux in such a foot most often lias two phalanges. In its commonest form the fivetoed foot departs from this normal in the fact that the hallucal rnetatarsus bears two digits instead of one. The morphological nature of these digits is obscure. Some have judged that one of them is a " prce-hallux ; " COWPER ' sees in the internal toe the true hallux, and argues that the digit commonly called the hallux is really the index ; HOWES and HiLL2 consider that the normal hallux has split into these two digits. The diversity of these views comes partly from an insufficiency of the area of fact over which the inquiry has been extended, for it will be found that the conditions are very various and shade off imperceptibly in several directions. As in all cases of Meristic Series, the first question relates to the position of these digits in the system of Symmetry of the limb. Are they in a Successive Series with the other digits, or do they balance them 1 Are they in Succession to each other or do they balance each other as images 1

Turning to the facts with these considerations in view it will be seen that no general answer can be given, but that the condition is sometimes of the one kind and sometimes of the other. For there are not merely two conditions, a four-toed and a five-toed, but there is a whole series of conditions and according to the cases chosen so may the question be answered. By examining a few score of fowls' feet many sorts may be seen. 590. (1) The most usual five-toed foot is that figured by COWPER (I.e., p. 249), in which the metatarsal of the hallux bears two digits, an outer one of two phalanges and an inner of three phalanges. For purposes of description let us call the outer the hallux. In this foot then the hallux is the least digit, and the members of the digital series increase in size on either side of it.

591. (2) But not rarely is found a state like the last save that the inner digit is borne by the proximal phalanx of the hallux. This is very common. The two digits may then be about equal in size, or more often the hallux is the smaller. 592. (3) Hallux more or less perfectly divided into two digits with a common base, having (a) two, or (6) three phalanges (as in HOWES' case Fig. 5). This state is practically that of the human "double-thumb" (see p. 350), and, just as in that phenomenon, the duplicity may be of various extent, often affecting only the nail and distal phalanx. Be- tween the two parts of such a double digit there is often that relation as of optical images found in human double-thumb, the curvatures of the two parts being equal and opposite. But if both digits are of good size and are separate up to the metatarsal this equality is rarely if ever found, and one of the digits, generally the innermost, is the larger. In this condition therefore there is a Succession from the hallux to the inner digit just as in (1). So the condition of double-hallux, that is to say the representation of one member of a series by two members in bilateral symmetry, shades off imperceptibly into the condition in which a new member is formed in Succession to the terminal member.

It should be noted that this case presents a remarkable difference from that seen in the like cases of variation on the radial side of the hand of Man. In Man the states of true double-thumb are just as in the Fowl; but if there is a difference or Succession between the two parts it is the ex(> rnal \vhi.-h is tin' un-ater, being in several cases a threephahniLT'l ili.irit shapnl like an index (seeXo. 486). Nevertheless in the Fowl it is tin- i/tf- i-iKil which is the greater.

The conditions in the following cases are not far removed from those named above. 503. Archibuteo lagopus ( K>iugh-legged Buzzard): specimen in good condition shot near Mum/, licinj.' otherwise normal. The toes of the left foot were placed as usual in a bird of pn-y, but on the outside2 of the hind toe was a much smaller accessary to.-. Tinry toe was ;ttta<-hed to the hind toe almost as far as tinbase of the claw of the latter. The claw of the accessory toe was half the size of that of the hind toe. In the left leg the muscles of the thigh and shank were less developed than usual. Toes of right foot abnormally arranged, being all directed forwards. The three normally anterior toes were on the inside of the series, and the toe which should properly be single and directed posteriorly was double and was directed anteriorly. These abnormally disposed toes were not functional. The right leg was much more developed than the left, and it seemed as if the bird had habitually stood on the rij_'ht leg. vox REICHENAU, W., Kosmos, 1880, vn. p. 318.

594. Oallinula chloropus (Moorhen): specimen killed in Norfolk in 1846. "Each of the hind toes possessed a second claw, which in the right foot merely springs from about the middle of the true toe, but in the left is attached to a second toe, which proceeds from the original one, about half-way from its junction with the tarsus." Extra toe and claw in each case attached outsideof the true hind toe. GUHNEY, J. 11.. and I'isiii.H, W. R., Zoologist, 11301.

Guinea-hen having double hallux; of the two digits the externalwas the longer. GEOFFROY ST HILAIKE, Ilixt. de Anom., i. p. 695. 595. Anas querquedula, L. (Garganey Teal): wild specimen having the left foot abnormally formed. In it there was no toe occupying the place of the hallux, but the digits II and III [using the common nomenclature] were partially bifurcated. In the digit III, the extremity only was divide 1, but each part bore a separate nail and there was no web between these secondary dibits, which were somewhat irregular in form. The digit II divided in about its middle into two nearly similar digits. which were united by a web. The nails of these digits were hypertrophied. Euco- LANI, Mem. Ace. Bologna, S. iv. T. in. p. 804, Tnr. in. /ir/. 1.

596. (4) From the condition seen in (3) it might be supposed that duplicity of the hallux is the least possible step in the progress of the four-toed form towards the five-toed. It is only one of the least possible steps. For in a few cases upon the base of the digit recognizable as the hallux, and standing in the normal place of the hallux, may be found a minute rudiment of a digit, sometimes with a nail, sometimes without. Between this and the well-formed fifth toe all conditions exist.

There are thus, as usual in the numerical variations of Meristic Series, two least conditions, one being found in duplicity of a single member, the other taking the form of addition of a rudimentary member beyond the last member. 597. Passing now from the simpler conditions of the variation to the more complex, several distinct states may be mentioned. The divergence from the normal may be greater either by the presence of two extra digits, or by change in the position of the extra digit or digits.

1 The only case to the contrary is that mentioned by WIXDLE, Jour. An, it. Phijs , ;xvi. p. 440, in which a three-phalanged digit stood on the radial side of a polk-x. This case has not been described. See pp. 3'Jt', uml 352. - In reading these records it should be remembered that owing to the backward direction of the hallux the apparent outside is morphologically inside, and probably this is meant in each case. Two extra digits are said to be not uncommon in the Dorking but I have myself seen only one case. A foot of this kind is figured by COWPER ', and in it the appearance is as of an extra digit of three joints (? all phalanges) arising internally and proximally to the hallucal metatarsal. which already bears two small and sub-equal digits. In the case seen by myself there was one large internal digit with three phalanges separately articulating with the tarso-metatarsus, and the hallucal metatarsus bore a digit divided peripherally, bearing two nails related as images. Here therefore there was a double hallux, and internal to it a separate digit.

598. The evidence regarding extra digits in other positions, though small in amount, is of importance as a light on the morphology of these repetitions of digits. We have seen that the ordinary extra digit is, with the hallux, borne on the hallucal metatarsal. In one of HOWES' cases (I. c. figs. 2 and 3) this metatarsal instead of simply articulating with the shank of the tarso-metatarsal was continued up to articulate also with the tibio-tarsus. From this state the condition in which a separate digit (or digits) articulates with the tibio-tarsus only is not far removed. Of this condition I know no detailed account in the Dorking, though it is referred to by LEWIS WRIGHT -, but I have met with the following cases in other birds.

599. Aquila chrysaetos (Golden Eagle): having two extra toes borne by right metatarsus [left foot is not described]. The two extra toes attached to upper part of the back of the metatarsus. Each bears a full-sized claw which was curved backwards and upwards. One of the toes bore six scutella on the morphologically upper surface and four on the plantar surface. The other toe, which was more completely united to the metatarsus along its whole length, bore only a single scutellurn on the plantar surface. The rest of the foot was normal. JACKEL, A. J., Zool. Gart., xv. 1874, p. 441, /u/-

600. Pheasant: right foot bearing a thin and deformed digit articulating internally with the distal end of tibio-tarsus. Hallux normal. Left not seen. Specimen received from Mr W. B. TEOETMEIER. (301. Pheasant: each leg bears a large extra digit of irregular form attached to the middle of anterior surface of tibio-tarsus. The two legs almost exactly alike, but in one the digit is firmly and in the other loosely attached to tibio-tarsus. Specimen kindly sent by Mr TEGETMEIEE.

602. Buteo latissimus c? , having extra digit on right leg, the toe was well formed, with two phalanges, bearing perfectly formed claw, loosely attached internally to tibio-tarsus just above articulation with tarso-rnetatarsus. COALE, H. K., Auk, 1887, iv. p. 331, fig. [Cp. No. 593.] 603. Turkey having two imperfectly separate digits [? images] attached to process of tibio-tarsus. Two cases differing in degree: hallux normal. ERCOLANI, Mem. Ac. Bologna, Ser. iv. in. PL in. jigs. 2 and 3.

604. Pheasant: somewhat similar case, in which two such digits were similarly placed, but one was large and the other small. Ibid., fig, 4. 605. tarus leucopterus. For the following case I am indebted to Professor E. RIDGWAY, Curator of the Department of Birds, in the United States National 2 "Perhaps the most difficult point in judging Dorkings, however, is to watch against malformations of the feet which have been fraudulently removed ; for the abnormal structure of the Dorking foot is very apt to run into still more abnormal forms, which disqualify otherwise fine birds for the show-pen. Birds are not unfrequently produced which possess three back toes, or have an extra toe high up the leg; or, in the case of the cock, with supernumerary spurs, which have been

known to grow in every possible direction We have on two occasions seen prizes awarded to birds which shewed unquestionable traces of such amputation...." The Illustrated Book of Poultry, 1886, p. 331. Mu-eum. The specimen is No. 76,221 in that collection, marked "Greenland, S.j.t. ls77; Loc. Kumlicn.' The accompanying figures were kindly made for me From a drawing of specimen in U. S. Nat. Mus., kindly made for me by Prof. RIDGWAY'S direction. under Professor Ridgway's supervision and sufficiently shew its structure (Fig. 122). [It will be seen that tin1 hallux in A, the right foot, appears on the outside; this I conceive is due to partial rotation to shew the abnormal toes.]

Besides these there are a few amorphous cases of extensive repetition of digits in birds. These facts shew how fruitless a work it is to try to find a statement \\liifli -hall includ'- all tincases. There is an almost unbroken series of conditions starting from either duplicity of the hallux, or from the presence of an internal rudimentary digit, up to a condition somewhat resembling that of " doublehand " in Man. If the first digit behind the hallux is the prsehallux, what are the digits on the tibio-tarsus ? If on the other hand the appearance of an extra digit internal to the supposed hallux is to be evidence that this " hallux " is the index, it may equally be argued that if two digits come up internal to the " hallux " then the supposed hallux is the medius, and so on indefinitely. Again, though with HOWES and HILL we may accept the cases of double-hallux as evidence that an extra digit may appear by division of the hallux, which is indisputable, we must equally accept the cases Nos. 597 and 598 as evidence that extra digits may grow directly from the tarsus or even from the tibia, though the hallux remain single and unchanged. And between these two there is no line of distinction ; they pass into each other. Do not these things suggest that we are looking for an order that does not exist ? Is it not as if we should try to name the branches of a tree in their sequences ?