Part 7 (1/2)

120. To give a clear idea of the relative uses of the bones and muscles, we will quote the comparison of another, though, as in other comparisons, there are points of difference. The ”bones are to the body what the masts and spars are to the s.h.i.+p,--they give support and the power of resistance. The muscles are to the bones what the ropes are to the masts and spars. The bones are the levers of the system; by the action of the muscles their relative positions are changed. As the masts and spars of a vessel must be sufficiently firm to sustain the action of the ropes, so the bones must possess the same quality to sustain the action of the muscles in the human body.”

121. Some of the bones are designed exclusively for the protection of the organs which they enclose. Of this number are those that form the skull, the sockets of the eye, and the cavity of the nose. Others, in addition to the protection they give to important organs, are useful in movements of certain kinds. Of this cla.s.s are the bones of the spinal column, and ribs. Others are subservient to motion. Of this cla.s.s are the upper and lower extremities.

119-128. _Give the physiology of the bones._ 119. How may the bones be considered? 120. To what may the bones be compared? 121. Give the different offices of the bones.

122. The bones are subject to growth and decay; to removal of old, useless matter, and the deposit of new particles, as in other tissues.

This has been tested by the following experiment. Some of the inferior animals were fed with food that contained madder. In a few days, some of the animals were killed, and their bones exhibited an unusually reddish appearance. The remainder of the animals were, for a few weeks, fed on food that contained no coloring principle. When they were killed, their bones exhibited the usual color of such animals.

The coloring matter, which had been deposited, had been removed by the action of the lymphatics.

123. The extremities of the bones that concur in forming a joint, correspond by having their respective configurations reciprocal. They are, in general, the one convex, and the other concave. In texture they are porous, and consequently more elastic than if more compact.

These are covered with a cus.h.i.+on of cartilage. The elastic character of these parts acts as so many springs, in diminis.h.i.+ng the jar which important organs of the system would otherwise receive.

124. The synovial membrane secretes a viscous fluid, which is called _syn-ovi-a_. This lubricating fluid of the joints enables the surfaces of the bones and tendons to move smoothly upon each other, thus diminis.h.i.+ng the friction consequent on their action.

_Observations._ 1st. In this secretion is manifested the skill and omnipotence of the Great Architect; for no machine of human invention supplies to itself, by its own operations, the necessary lubricating fluid. But, in the animal frame, it is supplied in proper quant.i.ties, and applied in the proper place, and at the proper time.

122. What is said of the change in bones? How was it proved that there was a constant change in the osseous fabric? 123. What is said of the extremities of the bones that form a joint? 124. What is synovia? Its use? What is said of this lubricating fluid?

2d. In some cases of injury and disease, the synovial fluid is secreted in large quant.i.ties, and distends the sac of the joint. This affection is called dropsy of the joint, and occurs most frequently in that of the knee.

125. The function of the ligaments is to connect and bind together the bones of the system. By them the small bones of the wrist and foot, as well as the large bones, are as securely fastened as if retained by clasps of steel. Some of them are situated within the joints, like a central cord, or pivot, (3, fig. 26.) Some surround it like a hood, and contain the lubricating synovial fluid, (8, 9, fig. 25,) and some in the form of bands at the side, (5, 6, fig. 23.)

[Ill.u.s.tration: Fig. 25. 8, 9, The ligaments that extend from the hip-bone (6) to the femur, (5.)]

[Ill.u.s.tration: Fig. 26. 2, The socket of the hip-joint. 5, The head of the femur, which is lodged in the socket. 3, The ligament within the socket.]

126. By the ligaments the lower jaw is bound to the temporal bones, and the head to the neck. They extend the whole length of the spinal column, in powerful bands, on the outer surface, between the spinal bones, and from one spinous process to another. They bind the ribs to the vertebr, to the transverse process behind, and to the sternum in front; and this to the clavicle; and this to the first rib and scapula; and this last to the humerus.

What is the effect when the synovial fluid is secreted in large quant.i.ties? 125. What is the function of the ligaments? 126. Mention how the bones of the system are connected.

127. They also bind the two bones of the fore-arm at the elbow-joint; and these to the wrist; and these to each other and to those of the hand; and these last to each other and to those of the fingers and thumb. In the same manner, they bind the bones of the pelvis together; and these to the femur; and this to the two bones of the leg and patella; and so on, to the ankle, foot, and toes, as in the upper extremities.

[Ill.u.s.tration: Fig. 27. 1, A front view of the lateral ligaments of the finger-joints. 2, A view of the anterior ligaments (_a_, _b_,) of the finger-joints. 3, A side view of the lateral ligaments of the finger joints.]

128. The different joints vary in range of movement, and in complexity of structure. Some permit motions in all directions, as the shoulder; some move in two directions, permitting only flexion and extension of the part, as the elbow; while others have no movement, as the bones of the head in the adult.

Explain fig. 27. 128. Describe the variety of movements in the different joints.