L 573 1

XXIII. On Hypsiprymnodon, Ramsay, a Genus indicative of a distinct Fumily (Pleopo- didae) im the Diprotodont Se'ectiom of the Marsupiuliw. B y Prof. OWEN, C.B., P.R.#., F..L.tY., gc., Superintemdent of the Nutural-History Departments irb the British Museum.

(Plates LXXI. & LXXII.)

Read January 17th, 1878.

T H E modification of the hind foot in the Marsupial series is peculiar in the way in which the digits depart from the typical mammalian number, 5. The peculiarity is chiefly shown by an atrophy of the second and third digits of a kind like that which affects the third digit of the fore foot in the Aye-aye-namely, attenuation without loss of length, and this in relation t o a special use distinct and apart from the foot as a loco- motive or prehensile organ.

Not only are the slender metapodials of the digits 11 and 111 (Pl. LXXII. fig. 10) wrapped up with the others in a common sheath of skin, but also the proximd and middle phalanges, leaving only the distal ones with their claws free, but in close contact and of equal length; and these claws have been uniformly observed in the Marsupials with, the so-modified hind foot to be used as scratchers and cleansers of the fur.

This condition of hind foot is found in carnivorous, frugivorous, and herbivorous Mar- supials, and is associated with as many distinct formulte of the dental system.

The modification of digits 11 and 111, moreover, may coexist with the normal develop- ment of the digits IV and v, and with an abnormal one of digit I, in the form of a powerful opposing hallux, as exemplified in the grasping hind foot of the scansorial phalangers (woodcut, fig. 1) ; or it may be associated with an abnormal development of the digits IV and v in both breadth and length, especially of IV, with a reduction of digit I to rudimental insignificance, as in the gradatorial Bandicoots (Perameles) ; or it may be associated with a still greater development of digits IV and v, and especially of IV, with total loss of digit I, as in the hind foot of the saltatorial Potoroos and Kan- garoos (woodcut, fig. 2).

But in the subject of the present paper a completely developed hallux (woodcut, fig. 3, P1. LXXII. fig. 7, I) is combined with the fur-cleansing and locomotive toes of the Poephaga* ; and this singular osculant condition of foot is associated with the dentition of the Hypsip~ymni~k. Thus the transitional character of the mammal under consideration would seem to place the genus between the scansorial and saltatorial groups of the great diprotodont division of the Marsupial order. The analogous approach in digits 11 and 111 to the Kangaroo type of foot made by the Bandicoots (Peramelide) may be a mere adaptive one in relation to their fur, and at any rate is an affair of one of the Polypro-

* 6' Outlines of a Classification of the Marsupialia," Trans. Zool. SOC. vol. ii. 1839, p. 332. t 6 Researches on the Fossil Remains of the Extinct Mammala of Australia,' 4t0, 1876, vol. i. pp. xii, 107.

SECOND SERIES.-ZOOLOGY, VOL. I. 4 G

5 74 FROF. OWEN ON IIYPSIPRY1CINODON.

todont suborder *, and must thcrcfore be set aside in the coiisidcration of the aEnities of ~yps@*yrnmodon, a genus mliich I regard as the type of a distinct group of the Diprotodontia, for wliich gro~ip, from the typical coinplcteness numerically of the toes, the name Pleopodidte f is proposcd.

Fig. 1. Fig. 3.

m

Fig.

Fig.

Fig.

1.

2.

3.

Sole,

Sole,

Sole,

hiid foot, of Phabnngista.

hind foot, of Kangaroo.

hind foot, of Hypsiprymnodon.

Fig. 2.

This group is at present represented by a single species, Hypsipryinnodon ~ O S C F Y U ~ Z G S , Ramsay, the description of which, unaccompanied by illustration, excited much interest, and a strong desire with the students of the Marsupial order to make a further acquaint- ance with the new form $.

I have recently been gratified by the reception of skins of mature male and female specimens kindly transmitted to me by the describer of the species, the present accorn- plished Curator of the Australian Museum, Sydney. The skull and bones of both fore and hind feet were included in the dried skins ; and these, being extracted, have afforded the materials for the following notes, which, with the accompanying illustrations (Plates LXXI. & LXXII.), may he acceptable to the Society, although they add little to the accurate description in the ‘ Proceedings of the Linnean Society ’ of the capital of one of our most remote and prosperous colonies.

* ‘ Researches 011 the Fossil Itemsins of the Extinct Nammals of Australia,‘ i t o , 1876, vol. i. pp. xii, 105. .f. 7rXtos, full; aoCs, foot.

‘‘ Bescription of a new Genus and Spccica of Itat-Kangaroo, allicd t o the Genus ffyps+i1’ryw27~~1s, now proposed to By E. Pierson Kamsay, P.L.S., C.X.Z.S.,” Proceedings of the Linnean Society be called H ~ ~ ’ s ~ ~ T ~ ” z ~ z o ~ ~ ~ L ~ ~ z moschntus.

of Xcm South Wales, TO^. i. pp. 33-35, 187G.

PROF. OWEN ON HYPSIPRYMNODON. 575

From the presence, direction, and relative size of tlie liallux, the EIyps@~ynzizodo?~ might be inferred to be a grasper, perhaps an occasional climbcr, though not so strictly arboreal as the Dendrolagues and Phalangers. I t s iicarest afiiiities, as shown by the skull and dentition, are to the ~ y ~ ~ s i p r y i i ~ n i d c e .

Both male and female of fIypsip?yrnln120C20ny as exeiiiplificd by the traiismitted skins, are of equal size; each measures 1 foot 3$ inches from snout to end of tail, this being 5 inches 9 lines in the female, 5 inches 4 lines in the male, of which the tip of the tail appears to be entire. The skins indicate a, rather long and slender-bodied quadruped, with a circumference at the haunches of about 8 inches, the trunk not tapering forward, as in the Potoroos, in which family also the smaller size of the female is notable, though the sexual difference of size is less in some of the Potoroos than in the Kangaroos.

If to a skull of 2 inches 7 lines (65 niillims.) in length 10 millims. be addcd for a snout shrunk in the dried skin, and 2 millims. for occipital integument, we get a length of head of 3 inches. The limbs are less unequal in length than in the Potoroos placcd by Mr. Waterhouse in his subgenus Poto7-om, the species of which have “the hinder legs shorter and the head more slender and pointed ” tha’n in the i!Yypsipry~imi proper.

I n the relative length of tlie head t o the body, and especially to tliat of the hind limb, .€Fyp23~ipi2yinnodon recedes from the Poephagous group, especially as exemplified in the Kangaroos and in such Yotoroos as Zypsz j~ iy i~ i ius ccmp&is, Gd., and .€Fypsi$7ym221s plcctyops, Gd. In this proportion Hypsipy izwus cqiccclis, Gd., comes aeasest to Hypsi- prymnodon.

The pelage of H y p ~ ~ i y i z i z o d o n vzoschatcs resembles that of the Potoroos, and differs from that of Bandicoots, in which the hair is of two kinds, the outwardly visible and longest being coarse and harsh to the touch, that beneath forming a soft, someliliat scanty fur. I n Hyps@iymoclon the fur is of moderate length, pretty closely applied, having numerous rather longer interspersed fine hairs, the visible portion of which is black or blacliisli, and pointed ; these are relieved by the dark- and light-barred colour of the visible part of the shorter hairs, all the liairs at their basal portions showiiig a leaden greyish tint. The tips of many of the shorter hairs are of a brighter brown than the rest, approaching to yellow. Mr. Kamsey describes the upper surface of the body of the living or recent animal as “ clothed with a close and rather stiff fur of rich golden colour mixed with black ; the head, face, and lower part, of the legs dark-brownish grey ; along the centre of the throat and chest a few patches of white ” *. These, in the skin of the male transmitted, are of a light yellowish tint; and the abdomen is a light brown. “ The young are of a more golden hue, and less white on the under parts ” +. The pelage is continucd by shorter hairs from the trunk over the base of the tail for half an inch or more, wlierc it abruptly ceases. The rest of the tail is nude and covered by reticularly disposed scales about 14 or 1 millim. in size to the graclually attenuated extremity. These scales are almost black on the transversely coiivex upperside, and of lighter leaden colour on the less convex underside. The diameter of the tail at the beginning of the scaly part is 8 niillims. A few miuute very short hairs project from

* 2 o l n . C i l . p. 3-1. 1. Iliitl. 4 ~ 2

576 PROF. OWEN ON HYPSIPRYMNODON.

the interstices of the scales, alniost requiring a magnifier for detection. The caudal cuticle is in the form of lacertian scales in many Potoroos ; but in these, as in Lagorchestes, the scales are partially hidden by short decumbent hairs, varying in position in different species ; the scaly tail is most sparingly clothed, and with short stiff hairs, in the sub- genus Poio~ous, Wth. On the head there are a few scattered supralabial, malar, and superorbital vibrissze, black, fine in texture, about an inch in length.

The muffle is nude, as in Bettongin and Potorozcs, the black naked skin being con- tinued a short way back from the upper part of the nose. The nostrils are lateral, opening close to the terminal nasal disk ; they are curved, with the convexity forward ; the disk is vertically grooved, and projects beyond the mouth. The lateral extent of the oral cleft is 1 inch (26 millims.). From the nose-tip to the eye is 1 inch 5 lines (36 millims.). The palpebral cleft is 11 millims. From this to the meatus auditorius is 22 millims. ‘‘ The irides are dark hazel ”*. The ears are rounded ; 20 millims. long by 22 rnillims. broad; the upper margin is slightly deflected. The basal half of the outer surface is clothed with short fine yellowish hairs ; the rest of the auricle is naked.

The limbs, fore and hind, are less unequal in length than in the Zypsipryrnnida? ; the forearm and paw measure 3 inches 2 lines (80 millims.), the leg and hind foot 4 inches 9 lines (122 millims.). The trunk does not taper forward, as in the Kangaroos, but maintains a more equable thickness in agreement with the more equal length and strength of the fore and hind limbs.

The first and fifth digits of the fore feet, (Pl. lxxii. fig. 5 ) though shorter and smaller than the rest, are by no means so reduced as in Perarneles ; they retain the general type of those in Eypsiprymnus. The pollex, I, is the shortest ; its claw does not extend beyond the base of the fore finger 11. The little finger, v, attains the distal end of the proximal phalanx of the finger, IV. The mid digit, 111, exceeds the adjoining ones by nearly the length of its claw. The claws are small, subcompressed, subdecurved, not broadened above, as in Bac~opus . The short hairs of the hand terminate at the base of the digits, the dorsal tegument of which is smooth and scaly. On the palmar side of the hand the hairs cease at the proximal border of the palm. This presents a pair of unequal longitudinally oblong callosities, and, in advance of these, three smaller ones near the base of the digits 11, IV, and v respectively. The longer hairs of the fore limb shorten, but less abruptly than in the hind limb, at about a third of an inch from the wrist. The callous pad beneath the hind foot extends from the base of the toes backward to the end of the heel, reducing the coating of short and adpressed dark brown hairs to a part of the upper surface.

The chief gradatorial toe, woodcut, fig. 3, IV, is not so disproportionately long and strong, nor is the fifth toe so weak, as in the Kangaroos and the more Kangaroo-like Potoroos. In the HypsLpqrnwidu? the proportions are most nearly approached by the species Potorozcs nzzcrinus. Kangaroo ; it is subcompressed, shorter and deeper than the cleansing-claws of II and 1x1.

The longer hairs of the leg terminate abruptly half an inch above the tarsus, like

The claw of digit IV has not the three-sided hoof-like character of that of the _.

* Tom. cit. p. 34.

PROF. OWEN ON HYPSIPRYMNODON. 577

the legs of a pair of trousers, beyond which the hairs become abruptly very short. They cease behind, leaving the heel bare, but are continued over the front and sides of the tarsus, along the upper surface of the metatarsus, and along that of the phalanges of toe IV as far as the claw. The dorsum of the second phalanx of the hallux and that of the same part of toe V, are covered by scaly integument, like birds' toes. The same integument covers the dorsum of the common sheath of the cleansing-toes 11 and III.

The skull of Hypsiprymnodort (Plate LXXII. figs. 1, 2, 3) is smaller, narrower, more elongated and attenuated anteriorly than in any known Potoroo-consequently departs further in general form from that of the Kangaroos. The alisphenoidal bulla is rela- tively smaller than in the Potoroos. The frontals are relatively narrower in proportion to their length than in most Potoroos, showing rather the form of those bones in some of the smaller Kangaroos and in the Dendrolagues. But the ridges continued back- ward from the postorbital processes are very faintly indicated in both sexes of Hypsi- prymnodon ; in DendroZagus they bound the temporal fossz above by a w ell-marked elevation : Hypsiprymnodon resembles Bypsipprymnus in this difference. The nasal bones are larger and narrower than in any Potoroo. Their pointed ends project 4 millims. in front of the naso-premaxillary suture. A line dropped from their tip would clear the front border of the foremost incisor. The length of the nasals is 1 inch 3 lines (31 millims.) ; their basal breadth 4 lines (9 millims.). The fronto-nasal suture is on a transverse parallel with the fore part of the orbits, not in advance thereof as in Potoroos ; its position is that which obtains in DendroZagus ; but it is transverse, not angular. The lacryma1 advances a little way upon the face ; it is grooved externally, and conveys the duct by a canal commencing in advance of the orbit, as in other Marsupials and in Birds.

The maxillary is pierced by two antorbital foramina, one small, 6 millims. in advance of the orbit; the other, which is larger, and answers to the normal foramen in Kan- garoos and Potoroos, is 8 millims. in advance. In Potoroos" and Eangaroos + the upper premolar descends more or less in advance of the antorbital foramen ; in Hypsiprymnodon the foramen is in advance of the premolar. The Potoroos differ from most Kangaroos in the longer and narrower facial part of the skull anterior to the zygomata, which part also tapers more anteriorly. Hypsiprymnodolz carries further this difference, the cor- responding part of the skull being relatively longer and more pointed than in Bypsi- prymnus cuniculus e. g. The extent of the maxillary in advance of the premolar exceeds that of the premaxillary ; in the Potoroos cited below reverse proportions prevail. The course of the maxillo-premaxillary sut-ure resembles that in the Potoroos : the crown of the small canine projects from the lower end of the facial part of that suture, as in Potoroos. The palatal plate of the maxillary has a pair of minute fora- mina on the transverse line a little in advance of the premolar. The chief vacuities of the bony palate are the two hinder ones, each half an inch in length, together 4 lines (13 millims.) in breadth; the pair of premaxillary fissures are relatively longer and

* Waterhouse, ' Mammalia { Hypsiprymnus penicillata, plate Ti. fig. 3 n ; Hypsiprymnus minor, plate viii. fig. 3 b. t Owen, Foss. Mamm. of Australia,' plate lxvi. fig. 1 (Oqhranter rufus) ; plate Ixxx. fig. 1 (Phascolagus erzcbcs-

tens) ; plate lxxxiv. fig. 1 (Halmaturus ualabcctus).

57s PROF. OWEN ON HYPSIPRYMNODON.

narrower than in Potoroos. The palatal vacuities are bound behind by slender trans- verse bars of the palatines, and extend forward to the interspace hetweeen the premolar and first molar teeth. Mr. Rarnsay rightly notes of the posterior palatal openings the character of the anterior margins meeting the exterior lateral at an acute angle *.

The breadth of the skull outside the zygomata is 1 inch 3 lines (32 millims.) ; the vertical diameter of the zygoma at the back part of the orbit is 5 millims. It does not increase posterior to this part, as in Kangaroos, but rather loses in that dimension as it extends to the tympanic bone.

3-3 1-1 The dental formula of Hgpsiprym.lzoc2o.n is that of t,he Potoroos, viz. i. 1--1, c. 1-1 4-4 P*1_1’ m. __ 4-4- - 30. The molar series in each jaw, according to characters of develop-

ment, include the teeth symbolized as y. 4, d. 3, m. 1, m. 2, m. 31.. I n some Potoroos (Eypsiprymnzs Gilberti e. g.) the crown of the premolar deviates from the longitudinal line of direction of the four following teeth by a slight turn outwards, and rather more so in the mandible $. A similar outward bend of the premolar is more marked in flypsi- prymnodon 9, in which the crown of the tooth, p. 3, presents the proportions shown in i9. Gilberti. In most Potoroos the fore-and-aft extent of the crown of the grooved and trenchant premolar is relatively greater. The molars in Hypsiprynznoclom repeat the proportions most common in the Potoroos, the last (m. 3) being the smallest, whilst in H. Gilberti the first (d. 4) is the smallest.

The length of the forearm and hand from tip of elbow to the nail, inclusive, is 3 inches 2 lines (80 millims.), of leg and foot, 4 inches 9 lines (122 millims.), of fore foot, in- cluding carpus, 1 inch 3 lines (30 millims.), of hind foot, including tarsus, 2 inches 6 lines (61 millims.), of face from tip of nose to base of ear 2 inches 5 lines (61 millims.).

The radius is more slender and of more uniform breadth than in Hypsiprymnzcs Gilberti or Bettongia penicillata (Pl. LXXII. fig. 0). I n these and other Potoroos the bone is pro- duced ulnad at its distal lower two thirds as a sharp plate. The length of the radius is 1 inch 9 lines (45 millims.) in Hypsiprymnodoru mosehatzs, but is only 1 inch 6 lines (40 millims.) in Rettongia penicillata, with twice the breadth, via. 5 millims. These differences are notable for the exigencies of palaeontology in reference to detached bones in caves, breccias, and drifts. The ulna of Zypsiprymnocloru is 2 inches 2 lines (55 millims.). The metacarpal and phalanges are longer and more slender in Hypsi- pyymnodon than in €@psipryriznus, save the ungual phalanges of 11, 111, and IV, which are both longer and stronger than in the Potoroos.

The tibia and fibula, after their proximal coarticulation, keep apart for more than half their length distad; in the rest of their course they are in close contact but not ankylosed. In Bettongia penicillatu the interosseous space occupies but one third of the proximal portions of the shafts of the two leg-bones ; in the rest of their extent the tibia and fibula are ankylosed, with a slight linear indication of their primitive distinctness.

The ulna and radius are in contact along their distal halves (Pl. LXXII. fig. 5).

* Tom. cit. p. 34. t ‘ Odontography,’ 1844 ; Proceedings of the Zoological Society, 1877, p. 358. t Plate LXXII . fig. 8. § Ik. figs. 3 8: 4.

PROF. OWEN ON HYPSIPRYMNODON. 579

The length of the tibia in Bettongia penicillata is 34 inches; in Hypsipyymnodon it is 2 inches 8 lines.

The length of the foot-bones in Hypsiprymnzcs Gilberti (Plate LXXII. fig. 10) is 4 inches 6 lines ; in Bettongia penicillata it is 3 inches 10 lines ; in Eypsipi-ymnodon (ib. figs. 6 & 7) it is 2 inches 5 lines.

The entocuneiform bone (ib. figs. 6 & 7, e) is proportionally larger, especially broader, than in the Potoroos in relation to the articulation of the metatarsal of the hallux, I. The rest of the structure of the tarsus adheres, save in the shorter proportion of the bones, to the Poephagous type, exemplified in plate lxxii. of my ‘Fossil Mammals of Australia.’

Mr. Ramsay states that the habitat of Hypiprymnodon moschatzcs is the Rockingham- Bay district, and that it frequents the dense and damp positions of the scrubs which fringe the rivers and clothe the sides of the coast-range. Here it is by no means rare ; but, from its retiring habits and the density of the forest, is difficult to obtain. The habits are chiefly diurnal, and its actions, when not disturbed, by no means ungraceful. It procures its food by turning over the debris in the scrubs in search of insects, worms, and tuberous roots, frequently eating the palm-berries (Ptychosperma Alexandm), which it holds in its fore paws, after the manner of the Phalangers, sitting up on its haunches, or sometimes digging. Seldom more than one or two are found together, unless accom- panied by the young. ‘( I n March 1874 I obtained from Mr. Broadbent a female with two young in the pouch, very small. During the same month a half-grown young one was shot in company with the adult male and female. They evidently breed during the rainy season, which lasts from February to May. Both sexes have a strong, although not disagreeable, odour of musk, which appears to be stronger in the female ”*.

In the skins transmitted to me the scrotum of the male was large, and in the usual marsupial prepudendal position t.. I n the female the orifice of the pouch was in the corresponding part of the abdomen $. Both the size and position of the hind thumb (woodcut, fig. 3) indicate the foot to be a grasper in a much lower degree than that of the Phalangers and Opossums. Mr. Rainsay does not, indeed, adduce any instance from his,own or his correspondent’s observations of the opposition, or the mode of oppo- sition, of the hallux to the other digits in the act of seizing or of climbing. Although it might be inferred, if the fruit of the Ptychosperma Alexandre was plucked from the branch and not seized after falling to the ground, that Hypsiprymnodon attained it by climbing.

Even in that case the act would seem to be occasional or exceptional; and the sum of the evidence tells for the ground-dwelling habits of this small and interesting Marsupial. The hallux here is, indeed, of more moment to the biologist in its homological than in its teleological relations. It points, as in the case of more rudimental and useless parts in other species, to the ancestral type.

Hypothetically, the earliest Marsupials are assumed to be pentadactyle ; and this assumption is supported by the following facts. The majority of the extinct Marsupiah

* Ramsay, tom. cit. p. 34. t Plate LXXI. fig. 1. $ Ib. fig. 2.

580 PROF. OWEN ON HYPSIPRYMNODON.

from British mesozoic formations are polyprotodont * ; and most of the existing species of that dental division of the Order are pentadactyle T.

Among the Diprotodonts $ the scansorial Marsupials retain the pentadactyle foot with a maximized hallux 4. In the gradatorial Diprotodonts, development has wrought on the two outer toes (IV and v), and especially on the fourth, with ultimate loss of the innermost or first toe. This modification, characteristic of the Potoroos, reaches its extreme in Mucropus and Chc~?ropzcs. The instructiveness of the foot of Hypsiprymnodolz lies in its indications of an early stage of modification of the pentadactyle type in the direction reached by the great Kangaroos. The fourth toe is, indeed, the largest (woodcut, fig. 3, PI. LXXII. figs. 6 & 7, IV), but not so much larger than the fifth (ib. v). The size of both, being less exaggerated, shows the cleansing-digits (ib. 11 & 111) on a less dwarfed scale. Finally, the hallux (ib. I) is not yet lost: it is small, indeed, and so placed as hardly to be opposable to any other digit, unless to the metatarsal part of 11.

As the habit of progression'on hard ground increased, the share taken by the fourth toe, as being most on a line with or most directly continuing groundward the tibia or main pillar of the leg, would determine a greater flow of blood to the moving powers of that toe ; and as the exercise of these powers would become more strenuous with the increase of weight to be so moved, especially when the motion was accelerated by leaps, so the fourth toe has come, at last, as in the great Boomer Kangaroo, to be almost exclusively the instrument applied to the resisting earth in the sdtatory made of locomotion.

I need hardly premise that the fifth toe in the foot of the Lizard is not developed in any bird. The first toe, or hallux, shows its opposable character and grasping function in the Perchers. When retained in a ground-bird, Apteryx e. g. (PI. LXXII. fig. 11, I), it is, as in Hypsipyrymnodo~~, minute, and placed above the level of the other toes. In the Cassowary (Pl. LXXII. fig. 12) it is lost ; the second toe (11) is reduced in length and breadth, but is provided with an unusually long and slender claw, which the bird may be seen occa- sionally to apply in preening the plumage ; the third toe (111) is that which has acquired the largest size and takes the greatest share in the act of support and progression ; the outermost toe (IV) is smaller, but not so reduced as the innermost (11, P1. LXXII. fig. 12). Here we have an analogous reduction to that shown in the Potoroo.

Finally, in the Ostrich, besides I , the next toe (11) is lost ; and the swift and powerful eourse of the bird is allotted, as in the Kangaroo, to the two outer toes, and mainly to one of these (111), the outermost toe (IV) being much reduced, but still characterized by its five phalanges (Pl. LXXII. fig. 13).

A thaumatogenist 11 may, indeed, contend that the species Xtyrwthio camelus was created, at the beginning, by primary power, with but two toes to each foot, in size,

The reduction of the toes in terrestrial birds follows an analogous course.

* ' Researches on the Fossil Remains of the Extinct Mammals of Australia, with a Notice of the Extinct Mar-

t Tom. cit. p. 105. 0 Art. UARSUPIALIA, ' Cyclopsedia of Anahmy,' 8v0, 1841, p, 285, fig. 111. /I ' Anatomy of Vertebrates,' 001. iii. 1868, p. 814.

supials of England,' 460, vol. i. pp. 12-75, plates i.-iii. (1877). $ Ibid. p. 107.

PROF. OWEN ON HYPSTPRYMNODON. 581

shape, and proportion best adapted to the need of this feathered denizen of the desert. But the nomogenist”, in reply, asks for the significance, or an explanation, of the retention of the metatarsal of the last toe (fig. 13, JI) , the jointless pointed extremity of which projects, like the splint-bone of the same lost toe in the Horse, on the inner side of the articular end of the huge metatarsal of the adjoining functional toe (111).

In speculating on the way of operation of the secondary law in the coming to be of species and genera distinguished, among other characters, by the number and pro- portions of the toes, a nomogenist has hazarded the following supposition :-“ as the surface of the earth consolidated, the larger and more produced mid hoof of the old three- toed Pachyderms [PaZ~otherium] took a greater share in sustaining the animal’s weight ; and more blood being required to meet the greater demand of the more active middle toe, i t grew ; whilst the side toes, losing their share of nourishment, and becoming more and more withdrawn from use, shrank ; and so on, according to the hardening of the ground, until only the hidden rudiments of metapodials [11 and IV] remained, and one hoof became maximized for all the work” t. The writer illustrates diis notion by a subjoined diagram of the structure of the foot in the ungulates of the Middle Eocene, the Miocene, and the Pliocene periods $.

But since the publication of the volume above cited, the structure of the foot of an older ungulate mammal, the Coryphoclort of our plastic clays, has been demonstrated by the fossils of that genus discovered by Professor Marsh in the corresponding Tertiaries of North America 11.

And here, as in the oldest known form of Marsupials, the primitive pentadactyle type of foot is revealed, from which the successive perissodactyle hoofed forms have deviated by concentration of size and force through strenuous use upon digit 111, and by degeneracy through opposite physiological conditions affecting size and power, first of digits I and v, which are lost in PuZaotJze?%mn, next of digits XI and IV, dmarfecl in Anchitherizcm and Zipparion, until finally these also disappear in Eqzczcs.

An analogous modification under other functions of the hind foot is traceable in certain extinct species of Bruta (Edentata, Ctw.).

In Mylodon digit I is obsolete; 11 is small, but retains the ungual phalanx; development is concentrated on III; the ungual phalanx is wanting and tlic others stunted, in IV and v 7 .

In Megatherium both digits I and 11 are gone; IV and v are clawless, stunted, and seem to have been developed in a common hoof-like callosity. The whole power of the foot as an uprooter is concentrated in digit 111 **.

* ‘ Anatomy of Vertebrates,’ vol. iii. 1868, p. 814. 0 Owen, ‘ British Fossil Mammals,’ 8vo, 1846, p. 299, cuts 103, 105. 1 1 marsh, “ Principal Characters of the Coryphodontidce,” American Journal of Science and Arts, rol. xir. July 1877,

p. 81, pl. iv. fig. 2. A more direct and continuous ancestry of existing Equines will shortly bc described and illustrated, in American Fossils, by the same author.

f- Torn. eit. p. 793. Ibid. woodcut 614.

7 Owen, ‘ Description of MyZocZon,’ 4t0, 1842, p. 117, pl. xxii. ** ‘ Memoir on the Negatherium,’ 4t0, 1860, p. 72, pls. xsv. and sxvi.

SECOND SERIES.-ZOOLOGY, VOL. I. 4 H

The degree and course of mutilation and of partial and exaggerated devclopment of certain tocs in the hind foot of other Bruta arc detailed in pp. 74-77.

582 PROF. OWEN ON HYPSIPRYMNODON.

I n thesc ponderous slom-moving quadrupcds the exercisc of the muscles and con- comitant vigour of circulation and innervation in locomotion was iufcrior to those affecting the main iiistrumcnt in the swift course of the IIorse and Kangaroo; the clam-bearing toe mainly (if not exclusively) exercised in exposing the ramifications of the root of the tree to be fellcd, was the subject of those influences which govern excessive or exclusive devclopnient.

I n conclusion, I may remark that the longest and strongest toe in the pentadactyle hind foot of the Lizards is the f o u ~ t h ; and I deem it indicative of the nearness to Saurians of the Implacentalia among niammals-an affinity so remarkably shown by nionotremes in other parts of the skeleton-that in the progressive reduction of the foot in Marsupials the fourth toe, IV, holds the preeminence.

I n the march of Man the chief motive power is concentrated on the innermost toe (I) as the main instrument, thence called the (‘ hallux,” or (‘ great toe.” I n this modi- fication of the foot for bipedal station and locomotion the huinan kind stands alone in the animal kingdom.

DESCRIPTION OF THE PLATES,

PLATE LXXI. Figs. 1 & 2. Hypsiprymnodon moschatus, Ramsay : nat. size. 1, male ; 2, female.

PLATE LXXII.

Fig. 1. Side view of the skull of Hypsiprymnodon moschatus, Rms. 2. Upper view of the same. 3. Under view of the same.

4. Upper view of the mandible of the same. 5. Bones of the forearm and paw of the same. 6. Bones of the hind foot : E, entocuneiform; I to v, digits. 7. The same, from the opposite (plantar) side. 8. Mandible of Bypsiprymnus Gilberti : c, canine ; P 3, premolar ; d 4, milk-molar ; M 1,2,3,

9. Bones of forearm and paw of the same.

figures are of the natural size.

I 1, 2, 3, incisors; c, canine; P 3, premolar; d 4 , milk-

Letters as in fig. 3. molar ; M 1, 2, 3, molars.

I, 11, 111, IV, v, digits.

molars. I to V, digits.

10. Bones of the hind foot, plantar aspect, of the same: 11 to v, digits.

11. Bones of the foot of Apteryx. 12. The same bones of the Cassowary ( C ~ S Z U W ~ U S ) . 13. The same of the Ostrich (Xtruthio).

All the above

The same letters are applicable to these three figiwes, viz. e, epiphysis; 2, 3, 4, metatarsals; I, 11, 111, IV, digits.