PROFESSOR OWEN ON LIMBS. *
Tars volume is one of that rare class of works where extensive know- ledge and animated science endow a seemingly narrow subject with large- ness, variety, and interest, by tracing its relations throughout their whole extent, illustrating their connexion by curious analogies, and endeavour- ing to deduce some primal law from the examination of the whole. The Bridgewater Treatise of the late Sir Charles Bell on the Hand was per- haps one of the most remarkable books ever written, for the profusion of its topics, the cogency of its conclusions, and the popularity of its man- ner. The range of Professor Owen is as extensive, his treatment more rigidly close, the law he would establish not so clearly settled, being in- deed from its nature less obvious. That man is indebted to his hand, perhaps rather to his thumb, for his superiority over all other animals— that without the human thumb the human mind could not give effect to its conceptions—is a law more readily perceived than that "arms and legs are developments of costal appendages."
The object of the Discourse on the Nature of Limbs is to endea- vour to discover the primal type of the limb—that original germ or pat- tern which is found everywhere,and whose numerous variations are to be considered developments. The survey is confined to the vertebrate ani- mals; because they alone have properly limbs, and, which to the lectu- rer is of more importance, the hard parts of the leg of a crab or insect, if ranked as limbs, would overturn his theory. The vertebrate animals are distributed by nature into several classes, with different habitations and different modes of locomotion. "They people the seas, and can move swiftly both beneath and upon the surface of the water ; they can course over the dry kind, and traverse the substance of the earth; they can rise above that surface, and soar in the lofty regions of aerial space.' Man can by sci-. ence accomplish somewhat similar feats : he can (naturally) walk the land, he can sail upon the waters, he can dive under them, he can tunnel the earth, and by means of a balloon he can rise into the air. The in- struments by which he accomplishes this are different, not to say oppo- site. In nature there is rather great variety than essential difference, that is, difference of type. The fin of the fish, the fore-limb of the mole, the wing of the bat, the fore-leg of the racer, the arm and band of man, appear "at sight" as different as they well can be; but, closely examined by the anatomist, not only do they all seem to have the same type, but the parts are answerable or homologous. There is the scapula or shoulder-blade, the clavicle or collar-bone, the single bone of the arm proper, the two bones of the fore-arm, the carpals, or collection of bones forming the wrist, and the digits. These are sometimes as distinctly marked in the lowest animals as in the skeleton of man, though with ex- quisite adaptation to their particular purpose ; sometimes the germs only of certain parts are found ; and sometimes a particular bone may be ab- sent, when it is not wanted,—as the clavicle in hoofed animals.
To trace these resemblances, and to exhibit them in their more marked developments, forms the first part of Mr. Owen's Discourse ; the text being illustrated by a variety of plates, which serve as substitutes for the skeletons that were probably used in the lecture at the Royal Institution. The second part is more argumentative than demonstrative ; and con- tains technical reasons in support of the Professor's own theory, in oppo- sition to the theories of some German anatomists, as to what is the arche- typal idea of a limb,—which examination results in the conclusion we have already mentioned. "Arms and legs therefore are developments of costal appendages. They are not ribs that have become free ; although liberated ribs may perform analogous functions, as in the serpents and the Draw volans.' If we adopt the ascending instead of the descending series—if we look at the lowest Apecimen, as in the fish, instead of the highest, as man —the fins will appear appendages to the ribs : and this, Professor Owen says, is the true mode of investigation. 'Most of the mistakes in the attempts to ascertain the typical or essential na- ture of parts of the skeleton, and almost all the impediments and opposition to the prosecution of this main end of anatomical science, have arisen from its study being ccnfined to that by-path in which it is usually commenced, viz, where the course of development has reached the highest form of animal life, in which mo- dification of each part in mutual subserviency to another is greatest, and the de- viation from the archetype is in the same degree. The rectification of the mis- takes and the acquisition of a more catholic feeling towards the study are gained by pursuing the broader high-road of organic nature, where those forms are of- fered to our contemplation in which vegetative uniformity most prevails, and the archetype is least obscured by purposive adaptations. "If, therefore, we find in that class which best displays the conditions for solv- ing the problem immediately before us, that the connexions of the scapular arch are such as to complete a typical segment, which otherwise would be abnormal by defect, we must conclude that the type is here adhered to; and that, although these connexions are abrogated in all the other vertebrate classes, they neverthe- less are the instantisc demotes,' and are exceptions in regard to the rule of the archetype, notwithstanding the actual mu-aerie:at superiority of the instances.
'On the Nature of Limbs. A Discourse delivered on Friday February 9, at an Evening Meeting of the Royal Itunitution of Great Britain. By Richard Owen, F.R. Published by Van Voorst.
"And the latter fact leads us to another consideration. This superiority was not always such as it now is. Time was when fishes were the sole representa- tives of the vertebrate sub-kingdom in this planet. Daring the long periods ante- cedent to the formation of the coal-measures, the vertebrate type was exclusively manifested by forms in the great majority of which the scapular arch was articu- lated to the oeciput. Subsequent changes in our planet have heightened and va- ried the conditions of animal existence, but the primitive pattern of the skeleton may be discerned beneath all the superinduced modifications."
The latter part of the discourse, will, in its details, only have an in- terest for anatomists ; indeed, other persons will not readily comprehend it. By aid of the plates, no doubt, the arguments of the author can be clearly followed ; but mere capability of understanding is hardly sufficient for interest. The reader requires to be familiar with the terms, or rather with the things they represent. The earlier exposition is of a more at- tractive kind, from the comparative easiness with which the facts and their bearing are understood. The treatment is clear and masterly, but not popular : a less scientific manner might perhaps have rendered the abstruser arguments more prehensible by the general reader. In par- ticular exposition the style is close ; in a wider field Mr. Owen sometimes rises to the effect of eloquence by the greatness of his subjects and his own capacity to handle them. The following example is from the perora- tion of his argument.
"We have been accustomed to regard the vertebrate animals as being charac- terized by the limitation of their limbs to two pairs, and it is true that no more diverging appendages are developed for station, locomotion, and manipulation. But the rudiments of many more pairs are present in many species. And though they may never be developed as such in this planet, it is quite conceivable that cer- tain of them may be so developed if the vertebrate type should be that on which any of the inhabitants of other planets of our system are organized.
"The conceivable modifications of the vertebrate archetype are very far from being exhausted by any of the forms that now inhabit the earth, or that are known to have existed here at any period.
"The naturalist and anatomist, in digesting the knowledge which the astrono- mer has been able to furnish regarding the planets and the mechanism of the satellites for illuminating the night-season of the distant orbs that revolve round our common sun, can hardly avoid speculating on the organic mechanism that may exist to profit by such sources of light, and which must exist, if the only conceivable purpose of those beneficent arrangements is to be fulfilled. But the laws of light, as of gravitation, being the same in Jupiter as here, the eyes of such creatures as may disport in the soft re&eted beams of its moons will pro- bably be organized on the same dioptric principles as those of the animals of a like grade of organization on this earth. And the inference as to the possibility of the vertebrate type being the basis of the organization of some of the inhabitants of other planets will not appear so hazardous when it is remembered that the orbits or protective cavities of the eyes of the vertebmta of this planet are con- structed of modified vertebrm. Our thoughts are free to soar as far as any legiti- mate analogy may seem to guide them rightly in the boundless ocean of unknown truth. And if censure be merited for here indulging, even for a moment, in pure epeculatmoo, it may perhaps be disarmed by the reflection; that the discovery of the vertebrate archetype could not fail to suggest to the anatomist many possible modifications of it beyond those that we know to have been realized in thiselittle orb of ours."
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