Part 6 (1/2)

These, by their natural affinities and anatomical structure, are an his scientific work as a e was study of the anatoreater part of his working life, he had more to do with the extinct forreat facility for preservation which their hard skeleton presents, as well as from the extremely iely in the study of palaeontology than does any other group In each of the great groups of vertebrate animals, in fishes, amphibia, reptiles, birds, and mammals, Huxley did important work Much of this is embodied in his treatise on _Vertebrate Anatomy_, but to some particular parts of it special attention may now be directed, as much because these serve as excellent examples of his method of work as because of their intrinsic i feature in the skeleton of vertebrate animals, and to the theory and structure of the vertebrate skull Huxley paid special attention, and his views and summary of the views of others fore This as put before the public in the course of a series of lectures on Coiven in 1863, while Huxley was Hunterian Professor at the Royal College of Surgeons, and the beginnings of it were contained in a Croonian lecture to the Royal Society in 1858

The theory of the skull which held the field was known as the vertebral theory The great bulk of the nervous syste along the dorsal line of the body and enclosed in a cartilaginous or bony sheath The nerve tissue is the brain and spinal cord; the sheath is the skull in front and the vertebral coluth of the animal The brain may be taken si in a general way to an expansion of the spinal cord in the region of the anterior liion of the hind li recently been shown in some extinct creatures to surpass the brain in size In a similar simple fashi+on the skull may be taken as an expanded anterior part of the vertebral colu as an expanded box for the brain, just as in the regions of the pectoral and pelvic expansions of the cord there are si bony case

We kno, froical development, that the brain contains structures quite peculiar to itself, and differs from the spinal cord in kind as well as in size; but, at the saurated, ee and the importance of its relation to anatomical structure were less considered What Huxley did was to show that the skull, in its in and real nature, was not merely an expanded portion of the vertebral column, but that it differed from it in kind

The hypothesis of the vertebral structure of the skull was due both to Goethe, the great German poet, and Oken, a most able but somewhat mystic Gerlish anato tried to rob Oken of the credit for this theory Huxley set that nation the unworthy suggestion Oken gave out his theory in 1807, and described how it had been first suggested to hisup a dried and battered sheep's skull, in which the apparent vertebral structure was very obvious, as, indeed, anyoneafter the theory had been made current, that the poet first publicly narrated that in a si before come to the sah announcing it later, Goethe had in reality anticipated the anatoe occurs in a letter to a friend, of a date in 1790, which admits of no doubt ”By the oddest happy chance, my servant picked up a bit of an animal's skull in the Jews' cemetery at Venice, and, by way of a joke, held it out to reat step in the for trait in Huxley's character, to find hireat h that man had been dead more than half a century; but it may be added that his just zeal was at least stiner of Goethe en, the conduct of whoard to Darwin and Huxley, Huxley had had just reason for resenting

The theory, then, which had dropped stillborn from Goethe, but which Oken developed, was simply that the skull consisted of a series of expanded vertebrae Each vertebra consists of a basal piece or centrum, the anterior and posterior faces of which are closely applied to the face of an adjoining vertebra, and of a bony arch or ring which encloses and protects the nervous cord Oken supposed that there were four such vertebrae in the skull, the centra being firmly fused and the arches expanded to form the dome of the skull Quite correctly, he divided the skull into four regions, corresponding to what he called an ear vertebra, at the back, through which the auditory nerves passed; a jaw vertebra, in the sphenoidal region, through which the nerves to the jaws passed; an eye vertebra in front, pierced by the optic nerves, and again in front a nose vertebra, the existence of which he doubted at first Quite rightly, he discriminated between the ordinary bones of the skull and the special structures surrounding the inner ear which he declared to be additions derived from another source So far it cannot be doubted that the vertebral theory e of the skull It was to a certain extent, however, thrown into disrepute by various fantastic theories hich Oken surrounded it Later on, Cuvier removed from it these wilder excrescences, and a theory of the unity of type of the skull throughout the vertebrates was based Cuvier, however, came to reject the theory, except so far as it applied to the posterior or occipital segment of the skull Later on, Owen resuscitated the theory, first throwing doubt on thethat Oken, instead of relying on the observed facts, had deduced the whole theory froh he made no new contribution to fact or theory in this matter, practically claimed the whole credit of it as a scientific hypothesis

When Huxley took up the subject, the position was that the vertebral theory was in full possession of the field, under the auspices of Owen Huxley began afresh froation was to settle once for all the question as to whether the skulls of all vertebrates were essentially modifications of the same type He took in succession the skulls of man, sheep, bird, turtle, and carp, and showed that in all these there were to be distinguished the saions: the basi-occipital, basi-sphenoid, pre-sphenoid, and ethmoid These were essentially identical with the centra of the four vertebrae of Oken Similarly, he showed the co the essential identity of the structures involved and of their relations to the nerve exits in the great types he had chosen In the series of lectures delivered before the College of Surgeons, he extended his observations to a er series of vertebrates, and substantially laid down the e of the skull In two important respects his statee, but an iuished the different modes in which the jaws may be suspended to the skull, and established for these different kinds of suspensoria the names which have ever since been eested by Oken, that the region of the ear is a lateral addition to the skull, and he distinguished in it three bones, his names for which have since become the common property of anatomists Finally, he made it plain beyond any possible doubt that the skulls of all vertebrates were built upon a co established the facts, he proceeded to enquire into the theory

There was now a newsuch probley, which, practically, had not been available to Oken, and of which neither Cuvier nor Owen had ations of a nu to these hi the facts which his investigations into coht, he shewed that the vertebral theory could not be h both skull and vertebral colue, are fashi+oned on lines so different as to exclude the possibility of regarding the details of each as mere modifications of a common type ”The spinal column and the skull start froin to diverge” ”It may be true to say that there is a primitive identity of structure between the spinal or vertebral column and the skull; but it is no more true that the adult skull is a modified vertebral column than it would be to affir the eical facts, he shewed that the skull arose out of elements quite different from those of the vertebral column The notochord alone is coitudinal cartilaginous pieces, non as the ”parachordals” and ”trabeculae,” of sense capsules enclosing the nose and ear, and of various roofing bones In the historical developrades becoe, as seen in A but a fibrous investrade, as seen in the skate or shark, where the skull is fore, very ie, seen in her aniher ani at first anervous inous, and, lastly, bony He made some important prophetic reical ould give to the distinction between cartilage and membrane bones--a prophecy that has beenand of others Our present knowledge of the skull differs froe of details We kno that throughout the series there is a priher in the scale than A the base and lateral walls of the skull This is tere; it is composed of the separate elements which Huxley indicated, and, in different aniested, the exact lies differ in extent, but occur in hoous situations This primitive skull is roofed over by a series of in with the other portions of the skull, and which have no representative in the vertebral column, but which are the direct descendants of the bony scales clothing the external skin in cartilaginous fishes In one respect only was Huxley erroneous Partly by inadvertence, and partly because the y becaists only after the elaborate work of Balfour of Cae, Huxley, in his account of the fors of the skeleton in the eroove, which, in reality, give rise to the nervous structures, and those embryonic tissues which forreat piece of hich we may take as typical of Huxley's contributions to vertebrate anatomy, is his classical study on the classification of birds The great group of birds contains a larger nuroup of vertebrates, and, in this vast assely little anatoht perhaps be taken as types of the extreh these differ in size, plu that can separate living things, the two conform so closely to the coe of the anatouide, down to minute details, for dissection of the other None the less, there are hundreds of thousands of species of birds between these two types It is not surprising that to reduce this vast assee of similar creatures to an ordered system of classification has proved one of the ists Before Huxley, it had been atteists; but, for the most part, these had relied too much on merely external characters and on superficial modifications in obvious relation to habits When Huxley, in the course of a set of lectures on Comparative Anatomy, was about to approach the subject of birds he was asked by a zoologist how he proposed to treat them ”I intend,” he replied, ”to treat them as extinct animals” By that he ed study of their skeletal structures the basis of his grouping, following the lines which Cuvier, Owen, and he himself had pursued so successfully in the case of the fossil remains of vertebrates The result was that this first systematic study of even one set of the anatoroup completely reforrapple with the probley was raised fro to a reasoned scientific study The immediate practical results were equally i the innurades of structure The lowest had already been recognised and named by Haeckel; it consisted of the Saururae, or reptile-like, birds, and contained a single fossil for birds by the presence of a hand-like wing in which the metacarpal bones ell developed and freelylizard-like tail actually exceeding in length the reroup of Ratites, although it contained only the Ostrich, Rhea, Emu, Cassowary, and Apteryx, he shewed to be equivalent in anatoroup of Carinates, which includes the vast roup, he laid most stress on the characters of the bony structures which form the palate, and by this simple means was able to lay down clearly at least the roup

Huxley's work upon birds, like his work in many other branches of anatoations of subsequent zoologists that it is easy to overlook its importance His employment of the skeleton as the basis of classification was succeeded by the work of others who made a similar use of the muscular anatomy, of the intestinal canal, of the windpipe, of the tendons of the feet, and many other structures which display anatomical modifications in different birds The modern student finds that all these new sets of facts are reater in bulk than the work of Huxley, and it is easy for hiested and inspired by the method which Huxley employed He finds that further research has supplanted some of Huxley's conclusions, and it is easy for hiested the investigations which haveand stiht simply because of the vast superstructures of new facts to which it gave rise

Closely associated with vertebrate anatoraphical distribution In 1857 the study of this iy was placed on a scientific basis, practically for the first tiraphical distribution of birds published in the _Journal_ of the Linnaean Society of London It was known in a general way that different kinds of creatures were found in different parts of the world, but little atteions characterised by their anietable inhabitants, as the political divisions of the world are characterised by their different governments and policies Mr

Sclater, o years later becaical Society of London, in hiswords:

”It is a well-known and universally acknowledged fact that we can choose two portions of the globe of which the respective fauna and flora shall be so different that we should not be far wrong in supposing them to have been the result of distinct creations

assu, then, that there are, or may be, more areas of creation than one, the question naturally arises how many of them are there, and what are their respective extents and boundaries; or, in other words, what are the ical divisions of the earth's surface?”

Mr Sclater's ansas that there are six great regions; Neotropical, Nearctic, Palaearctic, Ethiopian, Indian, and Australian, and his ansith reat wealth of detail, has been accepted by zoology

Two years later, however, Darwin gave a newand a new importance to Sclater's work, by the new interpretation he caused to be placed on the words ”centres of creation” Sclater's facts and areas remained the same; Darwin rejected the idea of separate creations in the older sense of the words, and laid stress on the iion and for the differences between regions by climatic differences and so forth He raised the questions of modes of dispersal and of barriers to dispersal, of si results produced by isolation He gave, in fact, a theory of the ”creations” which Mr Sclater had shewn to be a probable assus that Huxley should make a contribution to a set of probley In 1868, in the course of a allinaceous birds and their allies, he made a useful attempt, nearly the first of its kind, to correlate anato shewn the diverging lines of anatoroup of creatures he had been considering, he went on to shew that there was a definite relation between the varieties of structure and the different positions on the surface of the globe occupied at the present tieographical position a necessary part of the whole idea of a species or of a group, and so introduced a conception which has becoard to the nuions into which the world may be divided, Huxley raised a number of problems which have not yet reached a full solution Mr Sclater had divided the world into six great regions: the Nearctic, including the continent of North Aeographers; the Palaearctic, coreater part of Asia; the Oriental, containing certain southern portions of Asia, such as India south of the Himalayas andAfrica, except north of the Sahara, and Madagascar; the Australian, containing Australia and New Zealand and some of the more southeastern of the islands of Malay; the Neotropical, including South America Huxley first called attention to certain noteworthy reseions of Sclater, and held that a pri the great land masses of the Northern Hemisphere with a part of their extension across the equator, and _Notogaea_, which contained Australia but not New Zealand and South Aenerally accepted as a modification of Mr Sclater's sche fashi+on to some very remarkable features in the distribution of animals Subsequent writers have considerably extended Huxley's conception of the si the more southern land areas They have pointed out that theidea of the distribution of land and water on the surface of the globe is to be got by considering the globe alternately from one pole and from the other In the south, a clump of ice-bound land, ithin the Antarctic Circle, surrounds the pole All else is a wide doues of land, South Areat land reat land masses expand in the Northern Hemisphere, and shoulder one another round the North Pole America is separated from Asia only by the shallowest and narrowest of straits; an elevation of a few fathoms would unite Greenland with Europe Science points definitely to soreat northern land area as the centre of life for at least the larger terrestrial forms of life We know that these arose successively, priher for birds; the pouchedthe antelopes and the lion; the le before the man-like apes Each wave of life spread over the whole area producing after its kind; then, pressing round the northern land area, it met a thousand different conditions of environment, different foods, eneenera and species But there was never a wave of life that was not followed by another wave In the struggle for existence between the newer and the older forradually driven southwards towards the diverging fringes of the land masses The vanquished left behind them on the field of battle only their bones, to beco to the extreme limits of the land, and many early types were utterly destroyed But others found sanctuary in the ends of the South, and such survivors of older and earlier types of life cause a siaea, although the extent of his region must be increased

Recently, however, there has been a recurrence to Huxley's suggested union of South America and Australia, based on new evidence of a direct kind, quite different froroups of naturalists have stated that there are similarities between the invertebrate inhabitants of Australia and of South America of a kind which makes the existence of a direct land connection in the Southern Hehino has recently described someto the Australian group of Dasyuridae, and Oldfield Thomas has described a new mammal from South America which is unlike the opossums of America and like the diprotodonts of Australia So that, while the general opinion has been against Huxley's division, Notogaea, in the strict ave to it, there has recently been an opinion growing in its favour

Huxley alsoan additional circu New Zealand into a separate region, distinct from Australia

On these points there is a balance of opinion against his views

Before leaving the subject of Huxley's contributions to vertebrate anatomy, the actual details of which would occupy far too reat iy of the new terms and new ideas he introduced into classification His s, orderly and comprehensive, and while, in innumerable minute points, from the structure of the palate of birds to the structure of the roots of human hair (actually the subject of Huxley's first published contribution to scientific knowledge), he added to the number of known facts, he did even ether the known body of facts To him are due not only the names, but the idea, that thecoanisation: the reptile-like Prototheria, which lay large eggs, and which have many other reptilian characters; the Metatheria, or her animals, which include all the common animals frorouped the vertebrates into three divisions, and named them: Ichthyopsida, which include the fish and Amphibia, creatures in which the aquatic habit dominates the life history and the anato birds and reptiles, on the close connection bethich he threw so ht; Mammalia

CHAPTER IX