would have been the very opposite. We see the reverse of a natural cause. We see design, and that is all we perceive. Truly may we say, how evident the indications of his agency, whose fingers have fashioned us, and in whom we live, and move, and have our being? But you will not overlook another curiosity in this wonderful part-the provision for turning the head. A. The plan of the spine, upon which the head is supported, forbids the turning of one bone upon another. Its joints are hinges, confining to one motion, that of stooping and bending merely. We cannot turn our breasts opposite to our feet. We see the wisdom of this, if only on one account,-the safety of the spinal marrow, which ought evidently to be spared every unnecessary motion. This is the principle of the spine through an extended series of more than twenty bones. But one exception was necessary to enable the head to turn, by a motion of its own, without always being at the trouble of turning the whole body. To admit of this, one solitary deviation is introduced. One bone of the neck, which is a part of the spine, is permitted to turn. round, and only one. The construction is this. The head, together with the first bone of the neck, forms a perfect swivel, like the head of a cane, made to twirl round upon the staff. There is a notch in the first bone which receives a pin that runs up into it from the second, making what mechanics would call a pin, or piv- ́ ̧ ot joint. Upon this joint the head has a firm and accurate motion within a certain extent on each side, as far as is necessary. B. Every part seems to be the most wonderful, till we hear another described. Still, one might almost tremble to think of turning the neck, after what anatoof the spinal marrow. mists say T. It is this which renders the mechanism truly remarkable. There was plainly a choice of joints to enable the head to turn. Now, anatomists invite our attention to the singular safety of the joint by which this motion is performed. A. There are several joints which would have permitted it. The bone which revolves might have been fitted with a cavity to the head of the bone immediately beneath. There are a number of these joints in the body. They are called ball and socket joints, in which the head of one bone is received into a cup or socket in the other. There is such a joint in the neighbourhood of the neck, at the shoulder blade; and no other kind is ever employed in the body, for a revolving joint, except in the single instance of the neck. They are all liable, however, to slip in some degree, in the socket; which while of no importance in any other situation, would have been dangerous to the spinal marrow. A smart blow might easily dislocate such a joint. But nothing can slip a pin joint, short of breaking the pin. B. I do not see how any atheist could ever have been acquainted with his own structure. T. Do you think of any striking resemblance to the works of art, in the mechanism of the neck? A. "When we nod the head, we use the hinge joint which lies between the head and the first bone of the neck. In turning the head round, we use the pivot joint which runs between the first bone of the neck and the second. We see the same contrivance and the same principle employed in the frame or mounting of a telescope." It is occasionally requisite to move the telescope up and down, as when we want to point it to a star which lies higher or lower than another. It is also required, that it should be able to take a circular motion, as when we want to remove it from one star and point it to another star, by the side of it. For the first motion, there is a hinge upon which the telescope plays up and down; for the next, there is an axis or pivot on which the hinge and the telescope upon it turn round togethThis is exactly the mechanism which is used in the motions of the head! er. T. You can turn the telescope, however, entirely round; but you are aware, it is not the same with the head. The head has only a certain degree of motion from side to side; and this is confined to a very small compass though sufficient for the purpose ;sufficient, that is, with the motion of the eyes, which nearly completes the circle. But for this limitation of the motion, I need not tell you the spinal marrow would have been in danger of being twisted or compressed. A most artificial contrivance is introduced, which prevents this danger-can you describe it? A. There are two ligaments, small, but exceedingly strong, which are attached to the joint in such a manner, as to allow it sufficient play, but not to admit of any motion beyond a certain extent. They are called the moderator ligaments, from a latin word signifying to moderate or check. B. Then, if I understand it, when we attempt to turn the head upon either side farther than would be safe, one of these cords immediately arrests the motion, like a check rope, such as we sometimes see employed on gates, doors, &c. and acting precisely upon the same principle. T. But there is another circumstance which it belongs to our present purpose to understand. You have seen that the structure of the skull is admirably adapted to preserve the brain from being jarred. Is there any harmony of provision for the same purpose, in the structure of the spine, that is, of the support on which the brain immediately rests? A. Between all the twenty-four bones of the spine there are springs introduced, of a substance resembling gum elastic or Indian rubber. They are cartilages or gristles; and may be seen to perfection in a loin of veal. They operate between the vertebræ as so many spring cushions, so that, when we jump or light heavily upon the ground, the violence of the blow is in some measure broken by the spring, and the jar is diminished upon the brain. "We can readily understand," says Dr. Bell, "how great the influence of these twenty-four joinings must be in giving elasticity to the whole column; and how much this tends to the protection of the brain. Were it not for this interposition of elastic material, every motion of the body would produce a jar to the delicate texture of the brain, and we should suffer almost as much in alighting on our feet, as in falling on our head." But there is another very curious provision for the protection of the brain; the curved form of the spine, which is that of an italic . Elastic as this bone is, yet if it were perfectly straight, a jar would have extended through it to the head with much more power. if we should place a ball upon the end of a long, straight Thus, spring of steel or whalebone, and strike the other end upon the ground, the ball would probably be shaken off by the concussion of the blow. But if we first bend the spring in the shape of the letter, we should see the ball would not be jarred, but would have an easy motion like a bird rising and falling upon a bending branch. Thus admirably calculated is the spine to carry the head without jar or injury of any kind. Fig. 10. The human spine, so named from a Latin word, signifying the vertebra. It will be seen that in bending backward, the processes will touch and prevent the motion; also, that the strongest processes are in the lowest division of the spine, where the loins are situated, and where the motions of the back are. gi eatest. In the middle portion between the vertebro B. B., it will be observed that the processes are almost in contact with one another; so that in this part the spine hardly admits of any flexure. The ribs, enclosing the heart, lungs, &c., are attached to this portion of the spine. and, consequently, any considerable bending would here be unsafe. In the upper division, the processes are again spread; this being required for the flexibility of the neck. T. Is this wonderful mechanism the same in all animals? A. "In quadrupeds," says Dr. Paley, “the number of the vertebra is from thirty to forty; in the serpent it is nearly one hundred and fifty." Nor is this all, with respect to the serpent. "Whereas in men and quadrupeds the surfaces of the bones are flat, and these sur |