with air, and it forms what is called the "Swimming Bladder," by the expansion or compression of which the fish can either diminish or increase its specific gravity in the water: the tube, when appended, opens at the back of the throat; in that respect it resembles a windpipe; and it obtains the name ductus pneumaticus.

2. The earliest example of the air-sac and tube, thus existing in a dormant state, as regards respiration, in the fish, being applied to breathing, is found in the class intermediate between them and reptiles, viz., Amphibia. These ichthyosaurians inhabit the margins of rivers and lakes, overflowed at one time, and dried up at others: they are, accordingly, bounteously supplied with both aquatic and terrestrial organs of breathing. Outside their bodies, they possess gills resembling those of fishes; and so long as their territory is submerged they make use of them. When the waters subside and they are stranded on dry ground, they take to the swimming bladder, or Lungs, within. Blood-vessels, conveying the impure blood, are freely distributed on that sac: and the animals have the power, by the expansion and contraction of the surrounding walls, or Thorax, of alternately filling it with air and emptying it again, through the pneumatic duct, or Trachea.

3. Except in the young of certain orders of the next class, Reptiles, the gills are entirely discarded; and respiration is performed exclusively according to the Concentrated system. But even in the most perfect, the mechanism of the organ is rude, corresponding to the animals of the class being coldblooded. In the majority, the Lungs present the appearance of membranous sacs, or swimming bladders, rather than that of true pulmonic structure. Again, the Ribs forming the boundaries of the thorax are either too flexible, in accommodation to their characteristic mode of progression by creeping; or are too inflexible, from being embarrassed with remains of the external skeleton. But the most notable imperfection consists in the absence of a diaphragm, or the muscular partition which divides the thorax from the abdomen. The lungs and the bowels occupy a common cavity. It deserves, however, to be remarked that Nostrils are seen first in this class. These tubes being rigid, and permanently open, furnish a supplementary inlet for the air, when its entrance into the lungs might be interrupted by

obstructions in the mouth, during the act of eating. The nostrils provide also a suitable locality for the organ of Smelling.

4. In the class which comes next, that of Birds, the improvements observed in the organ relate principally to its use in decarbonising the blood. As these feathered animals are designed for flight, they are constructed to be extremely buoyant. That lightness is attained by the air which they respire being conducted by tubes and cells over their whole bodies; consequently, they have a disproportionately large quantity of air constantly passing through their lungs: the blood is, therefore, more perfectly aërated than in the animals below them; and they are warm-blooded. However, there is the same great want in them as in reptiles, that of a diaphragm. Nevertheless, Birds contribute to the sum of the improvements effected in the organ generally, by furnishing a true vocal organ; it is in them that we perceive the earliest appearance of a proper Larynx.

5. Ascending to the next class, Mammalia, we find carried out to its greatest perfection the principle of the system of Concentrated respiration. And that advancement is mainly due to the introduction into the formation of the chest of the Diaphragm; which is at once the means of confining the lungs, together with the heart, in a separate compartment, and of giving great additional force to the acts of breathing.

It is with this important stride in the process of development of the organ that we perceive, most distinctly, the fulfilment of the grand design of converting the apparatus of respiration into the instrument of Voice. By the thorax being now adapted to expand its cavity to a large extent in inspiration, and to contract it forcibly in expiration, it is capacitated to fill the lungs. with air, on the one hand, and to expel it, on the other, in ample volumes, with a powerful impulse. Accordingly, the air, being thus forcibly expelled, can be thrown, in its passage through the larynx and mouth, into the special vibrations which produce varieties of Sounds.

It is interesting here to observe how new structures, which would have been useless had they been added to the organ at a previous stage of its development, are introduced in correspondence with its increased powers. I refer now to the Lips. These appendages of the mouth are first met with in Mammalia.

And the original use to which they are applied relates to the mode of rearing their young, which gives to animals of this class their particular designation. Lips are indispensable for suckling; and that act could not have been performed unless nostrils had been previously furnished, and unless the chest had been constructed so as to allow the young mammal to draw deep inspirations.

But a higher office awaits the Lips in Man. These fleshy fringes are essentially required to adapt the mouth for Voice and Articulate language. Lips are also important parts of the features of the Countenance; and they are, therefore, constituents of the principal organ by which feelings and emotions, too refined for speech, are made known-that of Expression.

And here an observation presses itself upon our notice, in reference to the influence which powerful emotions, as witnessed in Man, exercise upon the organ of respiration, including the countenance. No structures of the body performing different duties are more closely allied to each other than the Heart, the centre of the circulating system, and the organ of Breathing. Throughout the whole animal kingdom, the development of each proceeds with equal steps. But it belongs to our present subject to attend only to the relation between them in the highest animal, Man. When the organ of respiration assumes the Concentrated form, the heart becomes also a Concentrated organ. By that expression is meant that the chamber of the heart previously appropriated, in the inferior animals, as a distinct muscular cavity, to circulating the impure blood through the lungs, is incorporated in Man with the chamber which sends the blood, when purified, over the whole body; so that the two cavities compose together an united organ, divided only by a partition. Accordingly, a material sympathy is established between the "pulmonic" and "systemic" cavities: they relax and contract simultaneously. From that arrangement, it follows that blood is propelled from one side into the lungs, and from the other side into the system, at each beat of the heart. Hence, if a disturbance sufficient to interrupt the currents should occur, its effects will be manifested both in the organ of respiration and in the body generally. Now it is a fact, of which every man's feelings make him conscious, that when strong emotions affect the mind, the heart, the "bosom's lord,” is correspondingly agitated. The consequence

is, that a momentary interruption, or a temporary acceleration, in the action of the heart is produced, accompanied with a sense of palpitation at the breast. In proportion as the blood is either hastened or retarded in its course to the body, particularly to the brain and skin, tremors, or paleness, or blushing will be observed: and according as it is driven to the lungs with undue impetuosity, or its flow is arrested, the breathing will be hurried, or slow, or alternate between the two states. Man is so constituted that he can interpret the changes to which these disturbances give rise. Prompted by a sympathetic sense, he reads instinctively, as a natural language, the signs of the troubled bosom in a fellow-man. And this mode of communication is intelligible to the inhabitants of every nation and clime, however diversified their articulate words. It is the language of Expression-a common link of all mankind.

Thus we perceive how, by a combination of extensive changes gradually wrought in the structure of animals, from the lowest to the highest, a fit instrument is at length constructed to minister to Man's highest endowment, the Mind. Following the development of one class of organs, we saw that, by the perfection attained in the structure of the instruments of Locomotion and Prehension in Man, the Mouth became freed from employing the jaws and teeth like the brutes; and that its cavity could, therefore, be reduced in size, the teeth set erect in close and uniform rows, and the whole form arranged and proportioned, for the articulation of words, in Speech. By following a parallel course of development in the organ of Respiration, we observed it constructed, in all the Invertebrata, on a plan inconsistent with its being applied at all to Voice. But in the Vertebrata, we saw the same organ gradually shaped and built up, by successive introductions of new structures, until it was converted into an instrument capable of propelling currents of vocalised air to the Mouth; thence to issue forth by the Lips, as articulate Words. If to Speech, thus wondrously provided, powerful emotion of the mind be conjoined, the organ will present itself in a new phase; words will be associated with the manifestations which that emotion creates in the body-Expression. When the Voice suffers interruption and falters, and the face, neck, and chest are animated by strong passion working from within the breast, human language exerts its most com

manding influence. Then the organ is beheld in its highest condition of development.

Such was the extensive course of observation pursued by the author, in endeavouring to solve the problem, why, in the higher animals and Man, there should be provided to the organ of respiration, in addition to the largely distributed class of double nerves, the Spinal nerves and Fifth-another series, consisting of nerves with single roots, derived from a distinct division of the brain. These nerves he conceived to be a superadded class, introduced to preside over the organ of breathing when it had assumed, in the Vertebrata, the extraneous office of acting as an instrument of Voice. Having observed that, in the transition from a simple apparatus in which the air of respiration is applied exclusively to oxygenating the blood, to a complicated mechanism in which the same air is employed also for the production of vocal sounds, material changes, including the annexation of new supplementary parts, were made in the organ, he inferred that these changes would be accompanied with corresponding modifications in the nervous system. As the superadded structures were moved by muscles, and regulated by sympathies, he argued that they would require to be provided with appropriate nerves. But he further thought that a supply of new nerves alone would not suffice,that it would be necessary that these nerves should have a centre of power seated in the brain and spinal cord. Hence he believed that, in conformity with the introduction of new portions of mechanism into the organ of breathing, there would be, not only an addition of appropriate nerves, but the development within the brain of a new division of its substance, endowed with influence over the nerves. Upon these grounds he concluded that the particular series of nerves which are characterised by being distributed to the organ of respiration, together with the portion of brain from which they arise, had been added, in the course of development of animals generally, to the preexisting "Original" system of nerves. And on account of the relation they bear to the organ of breathing, he applied to them the name "Respiratory" system.

When the nerves included in the two foregoing classes-the "Original" and the "Respiratory"-had their respective places assigned in the arrangement, nearly every nerve throughout

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