THE SKULL. 



205 



JSmily. Pray, what may these provisions be ? I never 

 was aware of the existence of any other provision, than 

 the mere vitality of the parts. 



> r . /?. -In a ll the moveable joints, we find a mem- 

 brane furnished with little glands, which pour out a soft 

 and viscid fluid ; this lubricates the joint, and by thus keep- 

 ing it constantly oiled, as it were, obviates the injurious 

 effects of friction. This fluid is called the synovia, and 

 is poured out in increased quantities, when the joint is in 

 use ; it seems as if motion was the proper stimulus of its 

 secretion. When, however, motion is continued too long, 

 the synovial glands are stimulated beyond measure, a 

 soreness is felt, and an irritation is thus created in the 

 joint, which may proceed to inflammation, and serious 

 consequences ensue. This effect may also be produced 

 by very different causes, that is, not a sufficient quantity 

 of motion to occasion the flow of the synovial fluid. 



Emily. You have not yet mentioned by what means 

 they are connected at the joints so strongly and securely. 

 Dr. B. This is done by means of very thick strong 

 ligaments which go from the extremities of the bones in 

 various directions, keeping them in their respective situ- 

 ations, and limiting their movements on each other. In 

 the hip joint a very broad ligament the thickest and 

 strongest in the whole body completely surrounds the 



whole joint, forming a 

 sort of bag in which the 

 bone moves with perfect 

 freedom. 



Thus connected to- 

 gether, the bones form 

 what we have already 

 termed the bony skele- 

 ton. At the summit we 

 observed the globular 

 bony box, called the 

 skull, composed of sev- 

 eral flat bones united by 

 18 



