THE ORGANS OF ANIMAL BODIES— THEIR FUNCTIONS. 



placed forwards, to aid in discovering their prey. Animals, though seldom susceptible 

 of musical notes, sometimes exhibit an aversion for the lovr or grave sounds. This is 

 remarkably the case with the Uon. In bats, the sense of hearing is surprisingly acute. 



L'orfane de la generation est done d'un sixieme sens, qui est dans sa 



peau interieure. 



Perhaps a greater claim to the right of being termed the sixth sense, may be estab- 

 lished in favor of that feeling of resistance, or muscular sense, by which we perceive 

 the degree of force exercised by particular muscles. The mouth and lips of a new- 

 born animal are directed by this sense to their proper function ; and the adult would 

 be in danger of a fall while engaged in walking, leaping, or other active exercises, if 

 he were for a moment unconscious of the present state of the muscles appropriated to 

 those actions. Shooting, bounding, and taking aim, presuppose a consciousness of 

 the degree of muscular exertion sufficient to produce a certain effect ; and instances 

 are not wanting of its surprising accuracy. Thus, the Indian fresh water fish called 

 the Chatodon rostratus, will hit an insect with a small drop of water at a distance of 

 several feet, and the encumbered insect speedily falls an easy prey. When the ele- 

 phant is annoyed by files, he will discharge a large quantity of water upon the part 

 attacked, with sufficient accuracy and force to dislodge them. The deadly spring of 

 the lion and tiger exhibits the instantaneous result of the muscular sense in its most 

 tremendous form. Dr Yellowley mentions the case of a woman who was afflicted 

 with the disease called aiKTsthesia, where the muscular sense of her hands was lost, 

 although the m-iscular power remained. On turning her eyes aside, she used to drop 

 glasses, plates, &:c., which were held in safety as long as another sense supplied the 

 place of the lost one. 



The stomach and intestines are possessed of certain peculiar sensations 

 •which declare the state of these viscera; and indeed every part of the 

 body is susceptible of sensations, more or less painful, when affected by 

 accident or disease. 



Pain teaches an animal to avoid hurtful objects, and is wisely given as a safeguard 

 to his frame: accordingly, its seat is mostly at the surface. The deep parts of the 

 body have but little sensation, as it would there be only a useless encumbrance. The 

 animal is continually warned, by uneasy sensations, to change his posture frequently, 

 to avoid high degrees of heat, and, in general, to accommodate his frame to surround- 

 ing circumstances. 



Many animals are defective both as to ears and nostrils, several are 

 destitute of eyes, and some are reduced solely to the sense of touch, which 

 is never wanting. 



In the higher animals, impressions made upon the external organs of 

 sense are transmitted by the nerves to the brain and spinal marrow, which 

 form the central masses of the nervous system. The elevation of an ani- 

 mal in the scale of creation may [frequently] be determined by the volume 

 of its brain, and the degree in which the power of sensation is concen- 

 trated there. Animals of a lower grade have the medullary masses much 

 dispersed ; and in the more simple genera, all trace of nerves seems to be 

 lost in the general substance of the body. That part wliich contains the 

 brain and principal organs of sense is called the head. 



We now proceed to consider the second animal function — namely voluntary 



MOTION. 



When the animal wills to move, in consequence of a sensation upon 

 an external organ, or any other cause, the motion is transmitted to the 

 muscles by means of the nerves. 



This power of originating motion, residing in the nervous system of living animals, 

 is one of the most wonderfid properties of their nature. Every machine, however 

 comphcatcd or varied in its structure, can only be set in motion by some external 

 power already existing in nature, or produced by art, whether it be the expansive 

 force of steam, the descent of weights, the action of running water, or the recoil of 

 a spring. No perpetual motion can ever be preserved by any arrangement of the 

 parts of a machine among themselves ; they must rest ultimately upon a prime mover. 

 But the exquisite arrangement of the animal frame surpasses, in this respect, the 

 highest mechanical skill. The mind wills — the muscle contracts. How much so- 

 ever we may desire to unravel the mystery, the process is inexplicable, and seems 

 for ever removed beyond the reach of human ingenuity. The only fact hitherto as- 

 certained is, that if the nerve be separated, seriously injured, or even tightly com- 

 pressed, the motion of the muscle will not follow the voUtion of the mind. 



The muscles are bundles of fleshy fibres, by the contraction of which 

 the animal body performs all its motions. The extension and lengthen- 

 ing of the limbs are equally the result of muscular contraction with their 

 bending and drawing in. They are arranged in number and in direction 

 to suit the motions which each animal is destined to perform ; and when 

 it becomes necessary to execute these motions with vigour, the muscles 

 are inserted upon hard parts, which are so articulated, one oyer the other, 

 as to constitute them so many levers. These parts, in the vertebrated 

 animals, are called bones. They are situate internally, and are formed of 

 a gelatinous mass [of cellular substance, the pores of which are] pene- 

 f.iated by particles of phosphate of lime. In some of the lower tribes of 

 animals, such as the MoUusca, the Crustacea, and the Insects, these hard 

 parts are external, and composed either of calcareous or of horny sub- 



stances, called shells, crusts, or scales, all of which are secreted between 

 the skin, and the epidermis or cuticle. 



A considerable difference is found between the chemical composition of the bones 

 belonging to the higher orders of animals and the external coverings of crustaceous 

 animals. Human bones, when analyzed by Berzelius, were found to contain in 100 

 parts nearly as follows : of animal matters, (being chiefly gelatine, cartilage, and mar- 

 row) 34 parts; of phosphate of lime, 51 parts; of carbonate of lime, 11 parts; of 

 fluate of lime, 2 parts; of phosphate of magnesia, 1 part; and of soda, muriate of 

 soda and water, 1 part. Here the principal ingredient is phosphate of lime; but in 

 the hard parts of crustaceous animals, such as crabs and lobsters, the carbonate of 

 lime is considerably in excess. The shells of the mollusca, such as muscles and oys- 

 ters, are almost entirely formed of the carbonate of lime. On the contrary, the horny 

 coverings of insects contain a very minute portion of earthy matter, and are mostly 

 composed of animal substances. The same proximate elements enter into the com- 

 position of horns, nails, and hoofs, being gelatine, with a membranous substance, re- 

 sembling the white of eggs boiled hard. The scales of fish are composed of layers of 

 membrane alternately with those of phosphate of hrae, which arrangement is the cause 

 of their brilUancy ; but the scales of serpents contain no phosphate of Ume, and very 

 much resemble, in their constitution, the horny coverings of insects. 



The fleshy fibres are inserted upon the hard parts, by means of other 

 fibres of a gelatinous nature, called tendons, which seem to be a con- 

 tinuation of the first. 



These tendons exercise the same ofBce as straps or ropes in ordinary machinery, 

 when it is required to transfer motion from one part to another. By this means a 

 moving power can be exercised, in a spot whore its immediate presence would be highly 

 inconvenient. Thus, the hand is moved by tendons communicating with muscles, 

 fixed at a considerable distance upon the arm ; and the velocity and delicacy of its 

 movements are not obstructed by their presence. Often these tendons are strapped 

 down by cross cords, and pass along grooves in the bones, or through a pulley formed 

 by a ligament. By these mechanical contrivances, the direction in which the muscu- 

 lar power acts may be changed; the forces of different muscles are compounded, and 

 altered in intensity; and the velocity of the resulting motions modified according as 

 circumstances may require. This arrangement also permits the accumulation of force 

 upon one point ; for a great number of muscular fibres are employed to contract one 

 tendon, in the same manner as several horses may be employed to draw the same rope. 



The peculiar shape observable in the articulated surfaces of the hard 

 parts confine the motions of the tendons within certain limits, and they 

 are still further restrained by cords or envelopes, usually called ligamenls, 

 attached to the sides of the articulations. Animals become enabled to 

 execute tlie innumerable motions involved in the exercise of walking or 

 leaping, fljing or swimming, according as tlie bony and muscular appen- 

 dages are adapted for these various motions; and also, according to the 

 relative forms and proportions wliich the limbs, in consequence, bear 

 among themselves. 



Nutrition, which we shall now explain, forms the first of the vegetative func- 

 tions. 



The muscular fibres connected with digestion and circulation are not 

 influenced by the Mill, but, on the contrar}', as we have already explain- 

 ed, their principal arrangements and subdivisions appear to be specially 

 intended to render the animal completely unconscious of their exercise. 

 It is only when the mind is disturbed by violent passions, or paroxysms, 

 that its influence is extended beyond tlie ordinary limits, and that it agi- 

 tates these functions common to vegetable life. Sometimes, when the 

 organs are diseased, their exercise is accompanied by sensation ; but, in 

 ordinary cases, digestion and circulation are performed without the con- 

 sciousness of the animal. 



The aliment is first masticated, tiiat is, minutely divided by the jaws 

 and teeth, or sucked in, when taken by the animal in a liquid form. It is 

 then swallowed entirely by the muscular action of the back parts of the 

 mouth and throat, and deposited in the first portions of the alimentary 

 canal, which are usually expanded into one or more stomachs, where the 

 food is penetrated and dissolved by corrosive juices. 



This gastric juice possesses the very remarkable property of dissolving most animal 

 and vegetable matters, when deprived of life, and some mineral substances. It more 

 especially acts upon such as yield nutriment to the animal, and are adapted to its gene- 

 ral habits and formation. WTien recently procured from the stomach of a healthy animal, 

 it appears as a clear mucilaginous fluid, shghtly salt to the taste. Substances, when 

 undergoing fermentation or putrefaction, are immediately checked in their action by 

 the gastric juice, and are formed by its corrosive influence into a new fluid, possessed 

 of entu-ely different properties, called chyme. But most mineral substances are indi- 

 gestible. Certain tribes of savages, as the Otomacs, will, however, swallow daily 

 large quantities of earth to allay the cravings of hunger. But this substance does 

 not appear to bo dissolved ; it merely acts mechanically in distending the stomach. 



The higher region of the ahmentary canal is occupied by the stomach, which re- 

 ceives the food conveyed to it through the cesophagus or gullet. The forn'. and 

 structure of the stomach bears a constant relation to the nature of the food. In 

 herbivorous animals, it is composed of a complicated system or reservoirs, where, by a 

 slow and intricate process, the small quantity of nutriment contained in vegetable 

 matter is abstracted and conveyed into the system. In carnivorous animals, the stomach 



