There is also a farther use to be made of the present example, and that is, as it precisely contradicts the opinion, that the parts of animals may have been all formed by what is called appetency, i. e. endeavour, perpetuated, and imperceptibly working its effect through an incalculable series of generations. We have here no endeavour, but the reverse of it; a constant renitency and reluctance. The endeavour is all the other way. The pressure of the ligament constrains the tendons; the tendons react upon the pressure of the ligament. It is impossible that the ligament should ever have been generated by the exercise of the tendon, or in the course of that exercise, forasmuch as the force of the tendon perpendicularly resists the fibre which confines it, and is constantly endeavouring, not to form, but to rupture and displace, the threads of which the ligament is composed.

Keill has reckoned up in the human body, four hundred and forty-six muscles, dissectible and describable; and hath assigned a use to every one of the number. This cannot be all imagination.

Bishop Wilkins hath observed from Galen, that there are, at least, ten several qualifications to be attended to in each particular muscle: viz. its proper figure; its just magnitude; its fulcrum; its point of action, supposing the figure to be fixed; its collocation, with respect to its two ends, the upper and the lower; the place; the position of the whole muscle; the introduction into it of nerves, arteries, veins. How are things, including so many adjustments, to be

made; or, when made, how are they to be put together, without intelligence?

I have sometimes wondered why we are not struck with mechanism in animal bodies, as readily and as strongly as we are struck with it, at first sight, in a watch or a mill. One reason of the difference may be, that animal bodies are, in a great measure, made up of soft, flabby substances, such as muscles and membranes; whereas we have been accustomed to trace mechanism in sharp lines, in the configuration of hard materials, in the moulding, chiseling, and filing into shapes, of such articles as metals or wood. There is something therefore of habit in the case; but it is sufficiently evident that there can be no proper reason for any distinction of the sort. Mechanism may be displayed in the one kind of substance as well as in the other.

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Although the few instances we have selected, even as they stand in our description, are nothing short perhaps of logical proofs of design, yet it must not be forgotten that, in every part of anatomy, description is a poor substitute for inspection. It is well said by an able anatomist *, and said in reference to the very part of the subject which we have been treating of :— Imperfecta hæc musculorum descriptio, non minùs arida est legentibus, quàm inspectantibus fuerit jucunda eorundem præparatio. Elegantissima enim mechanicês artificia, creberrimè in illis obvia, verbis nonnisi obscurè exprimuntur: carnium autem ductu, tendinum colore, insertionum proportione, et trochlearium distributione, oculis exposita, omnem superant admirationem."

* Steno, in Blas. Anat. Animal, p. 2, c. 4.

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CHAP. X.

OF THE VESSELS OF ANIMAL BODIES.

THE circulation of the blood through the bodies of men and quadrupeds, and the apparatus by which it is carried on, compose a system, and testify a contrivance, perhaps the best understood of any part of the animal frame. The lymphatic system, or the nervous system, may be more subtile and intricate; nay, it is possible that in their structure they may be even more artificial than the sanguiferous; but we do not know so much about them.

The utility of the circulation of the blood, I assume as an acknowledged point. One grand purpose is plainly answered by it; the distributing to every part, every extremity, every nook and corner of the body, the nourishment which is received into it by one aperture. What enters at the mouth finds its way to the fingers' ends. A more difficult mechanical problem could hardly, I think, be proposed, than to discover a method of constantly repairing the waste, and of supplying an accession of substance to every part of a complicated machine, at the same time.

This system presents itself under two views: first, the disposition of the blood-vessels, i. e. the laying of the pipes; and secondly, the construction of the engine at the centre, viz. the heart, for driving the blood through them.

I. The disposition of the blood-vessels, as far as regards the supply of the body, is like that of the waterpipes in a city, viz. large and main trunks branching

off by smaller pipes (and these again by still narrower tubes) in every direction, and towards every part in which the fluid, which they convey, can be wanted. So far the water-pipes which serve a town may represent the vessels which carry the blood from the heart. But there is another thing necessary to the blood, which is not wanted for the water; and that is, the carrying of it back again to its source. For this office a reversed system of vessels is prepared, which, uniting at their extremities with the extremities of the first system, collects the divided and subdivided streamlets, first by capillary ramifications into larger branches, secondly, by these branches into trunks; and thus returns the blood (almost exactly inverting the order in which it went out) to the fountain whence its motion proceeded. All which is evident mechanism.

The body, therefore, contains two systems of bloodvessels, arteries, and veins. Between the constitution of the systems there are also two differences, suited to the functions which the systems have to execute. The blood, in going out, passing always from wider into narrower tubes; and, in coming back, from narrower into wider; it is evident that the impulse and pressure upon the sides of the blood-vessel, will be much greater in one case than the other. Accordingly, the arteries which carry out the blood, are formed of much tougher and stronger coats than the veins which bring it back. That is one difference: the other is still more artificial, or, if I may so speak, indicates still more clearly, the care and anxiety of the artificer. Forasmuch as in the arteries, by reason of the greater force with which the blood is urged along them, a wound or rupture would be more dangerous than in the veins,

these vessels are defended from injury, not only by their texture, but by their situation; and by every advantage of situation which can be given to them. They are buried in sinuses, or they creep along grooves, made for them in the bones; for instance, the under edge of the ribs is sloped and furrowed solely for the passage of these vessels. Sometimes they proceed in channels, protected by stout parapets on each side; which last description is remarkable in the bones of the fingers, these being hollowed out, on the under side, like a scoop, and with such a concavity that the finger may be cut across to the bone, without hurting the artery which runs along it. At other times, the arteries pass in canals wrought in the substance, and in the very middle of the substance, of the bone: This takes place in the lower jaw; and is found where there would, otherwise, be danger of compression by sudden curvature. All this care is wonderful, yet not more than what the importance of the case required. To those who venture their lives in a ship, it has been often said, that there is only an inch board between them and death; but in the body itself, especially in the arterial system, there is, in many parts, only a membrane, a skin, a thread. For which reason this system lies deep under the integuments; whereas the veins, in which the mischief that ensues from injuring the coats is much less, lie in general above the arteries; come nearer to the surface; are more exposed.

It may be farther observed concerning the two systems taken together, that though the arterial, with its trunk or branches and small twigs, may be imagined to issue and proceed, in other words to grow from the heart, like a plant from its root, or the fibres of a leaf