faculties.' The functions of the eye depend greatly LETTER on the part called the Tubercula quadrigemina." 23 The CEREBELLUM, at the back part of our brain, is most connected with our bodily movements. 24 The MEDULLA OBLONGATA is essentially concerned in the functions of our breathing, which cannot be continued without it; and it co-operates in what is performed by the spinal marrow.25 It seems to be the most important part of the brainous system in all the functional operations of our frame. 26 'The vital offices of the SPINAL MEDULLA are now reduced to conveying to the muscles the motive impulse of volition, and to propagating to the sensorium commune, impressions made on the external senses. 27 It does not originate muscular motions. It is divided by a double furrow into two lateral halves; and each of these is again subdivided into two 22 Its removal occasions a state resembling idiotism, characterized by the loss of the power of discriminating external objects; which however co-exists with the faculties of sensation.' Henry, p. 66. 23 The tub. quad. preside over the motions of the iris; and their integrity seems essential even to the functions of the retina.' Ib. p. 90. 24It may be regarded as nearly established by modern researches, that the cerebellum is more or less directly connected with the function of locomotion. Rolando found that injuries of the cerebellum were always followed by diminished motive power.' Ib. p. 68. 6 25 The medulla oblongata exercises the office of originating and regulating the motions essential to the act of respiration.' Ib. p. 91. It is continuous in structure with the spinal marrow, and enjoys, by this relation, the same function of propagating motion and sensation.' Ib. p. 72. 26 The cerebrum may act without the cerebellum; and this latter organ continues to regulate the motions of the body, after the removal of the cerebrum; but the functions of neither survive the destruction of the medulla oblongata, which seems to be the common bond and central knot, combining all the individual parts of the nervous system into one whole.' Ib. p. 72. IX. IX. LETTER columns, one posterior, and one anterior.'28 The sensations from external things are conveyed to the soul by the posterior columns: and by the anterior ones, its will directs and produces the movements of its limbs and body.20 The nervous roots and their continued fibres or extensions spring separately from these distinct columns, and carry with them, as they spread and branch, their several properties and functions; the one sensorial, the other motive.30 There is no necessary dependence of the motions of the heart, and the other involuntary muscles, on the spinal 32 Of the NERVES, some are nerves of motion only, and are confined to the performance of it;" others, and a large number, are nerves both of motion and sensation, which proceed in their distinct columns from the spinal medulla;33 a few nerves minister to 28 Henry, p. 75. 29 Ib. p. 76. These two vital offices reside in distinct portions of the spinal medulla-the propagation of motion in its anterior columns, the transmission of sensations in its posterior columns.' Ib. p. 91 30 € Thus, each spinal nerve is furnished with a double series of roots; one set of which have their origin in the anterior medullary column, and one in the posterior. In consequence of this anatomical composition, the spinal nerves are nerves of two-fold functions, containing, in the same sheath, distinct continuous filaments from both columns.' Ib. p. 76. 31 Ib. p. 91. 32 The class of nerves exercising the single office of conveying motion, comprehends the third, fourth, sixth, portio dura of the seventh, the ninth, and perhaps two divisions of the eighth, viz. the glossopharyngeal and spinal accessores.' Ib. p. 80. Three of these nerves, the third, sixth, and ninth, arise from a tract of medullary matter, continuous with the anterior column of the spinal marrow.' Ib. p. 83. 33There are thirty-two pairs of nerves, which possess the two-fold office of communicating motion and sensation. All of these, excepting one, the fifth pair of the cerebral nerves, spring from the spinal marrow. These thirty-one pairs are all constituted of two distinct series of roots IX. the senses of sight, smell and hearing." Here again LETTER is a remarkable instance of the designing and factitious structure and specific composition and appropriation of every part of our frame. The olfactory, auditory and optic nerves are gifted with a special sensibility to the objects of the external senses to which they respectively minister. The one receives sensations from what is odour, and from that only; the second from sound, and from sound alone; the third solely from the impressions of sight; but altho exquisitely sensitive of these several things, neither of them have any sensation, any feeling from the touch. These nerves are insensible to ordinary stimulants, and possess an exclusive sensibility to their respective objects-odorous matter, light, and aërial undulation.' 35 The remainder of the nerves form the ganglionic system, or, according to Bichat, are nerves of organic life. These are comprised in the great sympathetic nerve and its associated plexuses and ganglia; but the functions of these are at present matter of discussion and conjecture. 36 roots; one from the anterior column, and one from the posterior column, of the spinal marrow.' Henry, p. 83. 34 This division comprises the first and second pairs, and the portio mollis of the seventh pair.' Ib. p. 91. 35 Ib. p. 91. Magendie seems to have been the first to prove, experimentally, that they do not share the common or tactile sensibility. He found the olfactory nerves, like the hemispheres of the brain from which they spring, insensible to pressure, pricking, or even laceration. The optic nerve, and the expansion on the retina, was as insensible to stimulants. The acoustic nerve was also touched, pressed, and even torn, without causing pain.' Ib. p. 87. 36 I quote Dr. Henry's report on this interesting subject, as the most concise, judicious, and correct summary of the modern discoveries on it that I have read, with a very candid statement of the claims and authenticated results of each discoverer. LETTER IX. I have submitted the observations and facts in this letter to your attention, in order that by studying yourself, and the origin of the knowlege and ideas which you already possess, you may perceive, and personally feel and keep in mind the grand truth, that human nature is not a casual, an undesigned, or a common or necessary course of things, or could have arisen in that way; but that it is in all respects, as much intellectual as bodily, a special, a chosen, and an artificial mode of being, devised by its Creator to be so; and specifically formed and caused in every one, by a vast series and complication of specific agencies and causations, successively operating to produce the very compound and particular results, which appear in ourselves and in all. It is this perception and conviction, that we are such factitious results from such special provisions purposely devised, made and arranged, in order to cause us to be what we are, that will give us the more adequate and intimate sense of the creating mind and power of the Deity; which will most strongly lead the understanding to a due recognition of Him, and to an habitual adoration and attachment to Him as an indispensable REALITY; without which, such a world and such an order of beings as ours, could not have come into existence. LETTER X. CONSIDERATIONS ON THE PLAN AND APPOINTMENT OF THE MY DEAR SON, X. THUS far we have been surveying some of the great LETTER principles on which human nature has been constituted, and which have been found to have operated, steadily and efficaciously, to fulfil their Divine Author's intentions. None have failed: they are continuing to act now as freshly and as vigorously as ever, but with more abundant results, as the human mind improves from their agency, and as our enlarging population and activity, are diversifying and multiplying the objects and success of man's emulating and highly cultivated spirit. It is the operation of such principles which forms the real Sacred History of the World; for this, in its incidents, only elucidates the workings of the intellectual springs and freely-combined mechanism and established powers, by which human beings are actuated, and their transactions produced, and their improvements effectuated. But what we have been contemplating, is only a part of the great system of our terrestrial nature. Other interesting portions of the Divine plan remain to be considered, and one of the most important of these will be the subject of the present Letter. It has been appointed from the origin of our race, |