Слике страница

this passage

raneous quadrupeds, the ears are short and lodged deep.

480. The structure of the ear is admirably contrived to collect the undulations of sound, and to convey them to the sensory in the brain. The first part is the auricle, or external ear, formed to stop and collect the sonorous undulations, and convey them to the concha, or large capacious round cell, at the entrance of the ear. Persons, whose ears are cut off, have a confused hearing, and are obliged to form a cavity round the ear with their hand.

In the interior is the auditory passage, curiously tunnelled and turned, to give sounds an easy passage, and prevent their too furiously assaulting the more tender internal parts. 481. To prevent the entrance of noxious insects,

is secured with a bitter nauseous substance, called ear-wax. The next principal part is the membranum tympani, or drum of the ear, with its inner membrane, the four little appendant bones and the three inner muscles to move them, and adjust the whole system to hear loud or soft sounds.

The passage behind the drum of the ear, is called the vestibulum, being the entrance to two other cavities, called the labyrinth, and the second cochlea, com its resemblance to a snail shell.

482. The principal organs of the sense of smeling are the nostrils and olfactory nerves; the ramifications of which are distributed throughout the nostrils.

Smelling is performed by the odorous effluvia in the air, being drawn into the nostrils by inspiration, and struck with such force against the olfactory nerves, as to shake them, and occasion ideas of sweet, fætid, sour, and aromatic.

483. The taste is that sensation which all things give to the tongue ; but some consider the palate, the upper part of the roaf of the month, to b4 the instument of taste.

The CREATOR seems to have established a very intimate union between the eye, the nose, and palate, by directing branches of the same nerves to each of these parts, by which means there exist all the necessary guards against pernicious food ; since, before it is admitted into the stomach, it undergoes the trial of two of the senses,

and the scrutiny of the eye. 484. Feeling is the sense by which we acquire ideas of solid, hard, hot, cold, &c.

Some consider the four other senses merely as modifications of feeling.

The immediaie organs of feeling are the pyramidal papillæ under the skin, which are little, soft, medullary, nervous prominences, lodged every where under the outermost skin.

Feeling is the most universal of our senses ; spiders, flies, and ants, have this sense in greater perfection than man.

In blind persons, the defect of sight has been supplied by their exquisite touch, or sense of feeling

485. From these five sepses, flow all our sensitive perceptions, the result of experience; and all the various habits, qualities, passions, and powers of animals.

Certain practices called instincts, not the apparent result of experience, appear to us to belong to some animals, contrived by some unknown means of that all-powerful CREATOR, whose wondrous and incomprehensible works inspire with rapture and devotion the being whom he has qualified to examine and estimate them,

Obs. To follow this wonderful scheme of creation into all its ramifications and variations, and to trace all its analogies, would fill hundreds of volumes, and occupy ages of observation; having, therefore, given the above general idea of animated existence in its relation to vegetables, I shall proceed to a brief enumeration of the Linnæn classes; referring my young students to Bingley's Animal Biography, to Buffon's Natural History, Mavor's Abridgment, and to a multitude of other books on such subjects.

486. As a prop-work, or substantial frame to the body, the bones are provided.

That the bones might not interfere with motion, they are provided with hinges or ligaments.

That the ligaments might work smoothly into one another, the joints are separated by gristles or cartilages, and provided with a gland for the secretion of oil or mucus, which is constantly exuding into the joints.

487. There are 248 separate bones in the human body, classed under those of the head, the trunk, and the extremities.

The skull, or cranium, consists of eight pieces, and serves as a vault and protection to the

brain. There are also the cheek-bones, the jaws, and 32 teeth imbedded in them.

The head is joined io the trunk by the vertebræ consisting of several short bones, to the upper part of which it is fastened by a hinge-joint, and turned in the socket of the next lower one by suitable muscles to the right or left.

488. In the front and centre of the trunk is the breast-bone, extending from the neck to the abdomen ; and opposite to it, in the back, is the spine, or backbone, which extends from the skull to the bottom of the loins, and is a long chain of separate short bones, called vertebræ.

These serve as the support of seven hoops or ribs, which are inserted in them, and from the chest or thorax, in which are the hecrt, lungs, &c.

Beneath them, inserted in the spine only, and extending but half way round the body, are five false ribs. The hip bones, with other bones attached, supporting the abdomen, are called the pelvis.

489. From the neck to the top of each arm, a bone extends on each side, called the collar-bone, and the blade-bones are independent supporters of it. Tho

that blood may,

bone extending from the shoulder to the elbow is called the humerus.

From the elbow to the wrist are two bones, the outer of which is the radius; the inner the ulna.

The thigh-bone is called the femur; the knee, the pateua ; and the leg has two bones like the arm, the inner called the tibia, and the outer the fibula.

490. The animal frame is constantly exhausted and renewed; so that every particle of the human body is changed in the compass of a year!

Nor is it less surprizing that so many different substances as compose every animal body, should also be secreted by the glands from the saine blood, than that

in every instance, be traced to grass for its origin.

Obs.-Those functions by which aliment is assimilated for the pourishment of the body, are digestion, absorption, circulation, respiration and secretion ! and the effect of such assimilation is called nutrition.

2. The food received into the stomach after mastication by the teeth, and being mixed with saliva, is converted into chyme by the gastric juice; the chyme passes into the intestines, where it is converted into chyle and excrementitious matter ; which Jast, being seperated by means of bile, is evacuated from the body; whilst the chyle is absorbed by the lacteals and conveyed into the blood vessels.

3. The absorbent system consists of the lacteals, lymphatics, the thoracic duct, and the glands called conglobate thronghout the body.

4. Glands are organic bodies consisting of blood-vessels, nerves, and absorbents, intended for the secretion or alteration of particular fluids. They are divided into four classes, simple, compound, conglobate, and conglomerate ; the orifices of glands are said to be peculiarly irritable.

5. Secretion is the process by which various fluids are separated from the blood by means of the glands. The secretions are divided into the saline, as sweat or urine; the oleaginous as the fat, cerumen of the ear, &c. the saponaceous, as bile and milk; the mucous, as on the surface of membrares, &c.

6. Sensibility is the faculty of perception by the contact of an extraneous body; and this principle is generally diffusred in our corporeal organs, but in different degrees. That modification of animal matter, in which sensation appears peculiarly to exist, is termed nervous.

7. Motion is effected by the muscular fibre contracticg by volition ; but the will can only exercise this power, through the medium of the nerves. Irritability is the power of contraction, inherent in our bodily organs, but not liable to be inluenced by the will.

491. All the senses of animals, and all their varied powers of action, are exactly adapted to their different species of existence. What is food for one, is poison to another; and every one finds provision according to its natural habits.

Every thing, also, is in exact proportion; and every provision of nature harmonizes with the corresponding desires and want.: of animals.

Nature's unnumber'd family combine
In one beneficent, one vast design ;
E'en from inanimates to breathing man,
An Heaven-conceived an Heaven-erected plan;
Onward, from those, who soar or lowly creep.
The wholesome equipoise through all to keep
As faithful agents in earth, sea, and air,
The lower world to watch with constant care :
Her due proportion wisely to converse ;
A wondrous trust, from which they never swerve.

PRATT's Lower World. 492. Linnæus divides Animated Nature into,

1. Quadrupeds (Mammalia), of which there are already known to man about 230 species.

2. Birds, of which there are about 1,000 species.

3. Amphibious Animals, of which there are about 100 species.

4. Fishes, of which there are about 500 species. 5. Insects, of which there are 2,000 species. And 6. Worms of which there are 800 species.

493. The first class of animated beings, called mammalia, comprehends all those that suckle their young ; and have warm red blood flowing in their arteries.

Their bodies, for the most part, are covered with hair, in quantity proportioned to the climate they inhabit. Beneath this covering, is a skin of various

« ПретходнаНастави »