THE PHRENOLOGICAL JOURNAL. No XVI. ARTICLE I. A COMPARATIVE VIEW OF THE RELATION BETWEEN THE DEVELOPMENT OF THE NERVOUS SYSTEM AND THE FUNCTIONS OF ANIMALS. By Thomas Sandwith, Surgeon, and Member of the Hull Phrenological Society, &c. "Whether the views of Gall and Spurzheim may be verified or not, our labours in this direction must be productive, must bring with them collateral advantage." LAWRENCE. (Read to the Hull Society, May 1827.) IN a former essay, of which the substance is known to most of you, an endeavour was made to prove, from the closest analogy, that the a priori objection against Phrenology, viz. that the brain manifested none of the separate organs described by its founders, was untenable, the objection being equally applicable to the established theory of the functions of the spinal chord. The nature of the evidence on which Phrenology is erected was exhibited. The science was also shown to be in harmony with many phenomena otherwise inexplicable, as monomania, drunkenness, dreaming, somnambulism, the reVOL. IV.-No XVI. 2 H sults of education, and national character. Several objections, having their origin in profound ignorance of compara tive anatomy, were refuted, and others adverted to,-such as the tendency of the new theory to materialism, atheism, &c., -as being at length exploded. It would have been an easy matter to refute another objection commonly made by pretenders to anatomical knowledge, viz. " that the form of the "cranium is no criterion of the configuration of the brain," a no less competent observer than Cuvier himself having said, “that in all "mammiferous animals the brain is moulded in the cavity of the "cranium, which it fills exactly; so that the description of the osseous part affords us a knowledge of at least the external form of "the medullary mass within." I have now the honour of calling the attention of the Society to another important consideration, viz. the relation that obtains, throughout the animal kingdom, between the development of the nervous system and the functions of animals. "The visible fabric of the brain "differs most widely in quadrupeds, birds, fishes, insects,—and "there is an equal difference in their intellectual phenomena, appe"tites and instincts, every variation in construction being accom"panied with a corresponding modification of function."+ The objectors to Phrenology are unwilling to believe the notion of the perfection or deficiency of the manifestations of any mental faculty being at all dependent on the size or form of a portion of the brain. If, however, the proposition just stated be established, its truth must be admitted. We shall observe also, as we proceed, abundant evidence of the truth of Messrs Gall and Spurzheim's theory of the origin of the nervous system, viz. " that it is not an unit, but consists of "many essentially different parts, which have their own individual "origins, and are mutually in communication." This proposition, which is collateral and independent of the former, it is desirable to keep in view. When we examine any given portion of the nervous system,—the brain, the spinal chord, the ganglions, or any part of these,―we can discover nothing of the functions which any of these perform. We do not, as in some of the other • Cuvier's Comparative Anatomy, vol. ii, p. 13. + Lawrence. organs, perceive a mechanical connexion between the structure and its particular uses; but when we take a comparative survey of the nervous systems of the entire animal kingdom, the result is very different. It is then "the simplifica"tion or degradation of the organization is immediately percep"tible." Perfection of function is seen in connexion with full development of nervous matter, deficiency with imperfect organization, and absolute negation of function, with a corresponding chasm in the structure of the nervous system: and this is true, not only "of the four great departments of the "animal kingdom, but is equally so in each department.”* Being strictly experimental, this evidence is highly valuable. To compare a perfectly organized animal, in which there is corresponding perfection of function, with another in which structure and function are alike defective, is the same in effect as to ascertain the functions of the more gifted animal by the mutilation of its organs. It is, indeed, with the exception of the facts supplied by pathology, the only kind of evidence open to the physiologist. The nerves themselves admit of mutilation and division, and to experiments of this kind we are indebted for our recent knowledge of the func tions of the spinal marrow. But when the centre of the system is invaded by the knife, many impediments besides death defeat the purpose of the experimenter. "The animals of "inferior classes," says Mr Lawrence," are so many subjects of experiment ready prepared for us, where any organ may be observed "under every variety of simplicity and complication in its own "structure of existence alone, or in combination with others."Being presented, then, with experiments prepared by the hand of nature, who has, as it were, performed the necessary mutilations, and left no wound or scar, and no embarrassing disturbance of function, it is our business to examine them with attention, in order to ascertain whether they agree with the conclusions at which we have arrived by their means. In the lowest order of animals, zoophytes, many of which seem to form a connecting link between the animal and vegeLawrence, p. 101. table kingdoms, and in some worms, which again connect zoophytic animals with the tribes above them, no nervous system is discoverable. The actions of these animals being apparently automatic, as in plants, which the radicated ones so greatly resemble, neither brain nor spinal chord are necessary; and indeed the existence of nerves has only been inferred from their being apparently endowed with sensation. But this mode of proof is by no means conclusive, since in them, as well as in the mimosa and other vegetables, which are sensible to the action of light and other stimuli,* sensibility may depend on inherent irritability,—a property, according to Haller and Wilson Philip, possessed by animals, and to which nervous power is superadded. Indeed, so long as a nervous system is denied to such remarkable vegetables as the Dionœa Muscipula, Hedysarum gyrans, and Vallisneria spiralis, there is no good reason, short of demonstration, why it should be assigned to zoophytic animals. Some zoophytes, however, as the long-armed Polypi, impelled by the sense of hunger, introduce food into their mouths by voluntary motions. In them, therefore, a nervous system of some kind or other must be admitted; but, as no distinct apparatus can be detected, Cuvier thinks that the nervous matter must be equally diffused over the whole body. To distinguish this kind of nervous system from the cerebro-spinal and ganglionic, it is called by Macleay the mollicular, each molecule being analogous to a ganglion or centre of sensation; and it is this supposed peculiarity which accounts for the vivaciousness of such animals, many of which, it is well known, may be multiplied by division. For, as Cuvier observes, "it is only in the animals that are most perfect, and "approach nearest to man, that the connexion of the different parts "of the nervous system, and the presence of its central parts, is ab"solutely necessary to the existence of the animal."+ We see, then, in the lowest link of animal existence, a re • Vide Smith's Introduction to Botany, p. 2. + Cuvier, vol. ii. p. 20. lation between the structure and functions of the nervous system. The evidence, indeed, is only inductive, but it strengthens and becomes positive as we proceed. The actions of the acephalous mollusca, which are next in order, are simply vital, and of course automatic; so much so, that being destitute of senses and voluntary motion, even the sexes are enclosed together in the same shell, in the same animal. We know that the actions of the vital organs, in vertebral animals, are involuntary, and, though remotely connected by the nerves with the animal powers, are to a certain extent independent of them. Of this truth the phenomena of plexy, concussion of the brain, &c. are illustrations. know also that their movements are owing to certain ganglia, which at the same time isolate and connect the vital and animal functions, and are reciprocally the same to each other. Such being the condition of the oyster, it has neither brain nor chord, but two ganglia, one at each extremity of the animal; and these are the sources of its visceral nerves. apo We Endowed with senses, instincts, and voluntary motion, the nervous systems of the cephalapodous mollusca, as the cuttlefish and calmar, and of the gasteropoda, as the snail and slug, approach nearer to that of vertebral animals, the inferior orders of which the former so nearly resembles. These creatures, indeed, have no spinal chord, but the nervous collar which encircles the oesophagus is probably analogous; and they have a brain in the head, bilobed in the cuttle-fish, and lunated in the snail, in both giving origin to the nerves of The head of the cuttle-fish is actually pierced with holes for the transmission of the nerves. Both have also a variable number of ganglia for the nerves of the vital apparatus connected to the brain and to each other. We know little of the instincts of the snail. In the actions attendant on one of the strongest of the passions it resembles the higher animals, and, as in those of the preceding class, its power of restoration is considerable, being able to regenerate a head and tail. One of the instincts of the cuttle-fish is curious. Underneath sense. |