kinds. Of this class are the bones of the spinal column, and ribs. Others are subservient to motion. Of this class are tho upper and lower extremities.

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 cushion of cartilage. The elastic character of these parts acts as so many springs, in diminishing the jar which important organs of the system would otherwise receivo.

124. The synovial membrane secretes a viscous fluid, which is called syn-o'vi-a. This lubricating fluid of the joints enables the surfaces of the bones and tendons to move smoothly upon each other, thus diminishing 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

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

supplied in proper quantities, and applied in the proper place, and at the proper time.

2d. In some cases of injury and disease, the synovial fluid is secreted in large quantities, 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.)

Fig. 25. 8, 9, The ligaments that extend from the hip-bone (6) to the femur, (5.) 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

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

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 vertebræ, 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.

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.

Fig. 27.

2

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 latera 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.

Fig. 28. 1, 1, The spinal column. 2, The skull. 3, The lower jaw. 4, The sternum. 5, The ribs. 6, 6, The cartilages of the ribs. 7, The clavicle. 8, The hunierus. 9, The shoulder-joint. 10, The radius. 11, The ulna. 12, The elbowjoint. 13, The wrist. 14, The hand. 15, The haunch-bone. 16, The sacrum 17, The hip-joint. 18, The thigh-bone. 19, The patella. 20, The knee-joint 21, The fibula. 22, The tibia. 23, The ankle-joint. 24, The foot. 25, 25, The ligaments of the clavicle, sternum, and ribs. 27, 28, 29, The ligaments of the shoulder, elbow, and wrist. 30, The large artery of the arm. 31, The ligaments of the hip-joint. 32, The large blood-vessels of the thigh. 33, The artery of the leg. 34, 35, 36, The ligaments of the patella, knee, and ankle.

Note. Let the pupil, in form of topics, review the anatomy and physiology of the ones from fig. 28, or from anatomical outline plates No. 1 and 2.

CHAPTER VII.

HYGIENE OF THE BONES.

129. The bones increase in size and strength by use, while they are weakened by inaction. Exercise favors the deposi tion of both animal and earthy matter, by increasing the circulation and nutrition in this texture. For this reason, the bones of the laborer are dense and strong, while those who neglect exercise, or are unaccustomed to manual employment, are deficient in size, and have not a due proportion of earthy matter to give them the solidity and strength of the laboring

man.

Observation. The tendons of the muscles are attached near the extremities of the bones. Exercise of the muscles increases the action of the vessels of that part to which the tendons are attached, and thus increases the nutrition and size of this portion of the bone. Hence the joints of an industrious mechanic or farmer are larger than those of an indi vidual who has not pursued manual vocations.

130. The gelatinous bones of the child are not so well adapted for labor and severe exercise as those of an adult. 1st. They are liable to become distorted. 2d. They are consolidated by the deposition of earthy material before they are fully and properly developed. If a young animal, as the colt, be put to severe, continued labor, the deposition of earthy

129-148. Give the hygiene of the bones. 129. What effect has exercise upon the bones? What effect has inaction? Why are the joints of the industrious farmer and mechanic larger than those of a person unaccustomed to manual employment? 130. Give the first reason why the bones of the child are not adapted to severe exercise. The second

reason.