160 DEVELOPMENT AMD HEREDITY. 



form of this rude ball, a point is subjected to greater 

 pressure than the surrounding parts, that point will 

 be reabsorbed or hindered in its growth until the 

 ball finally presses evenly on all parts of the socket. 

 We know that the toes of civilised people become 

 reduced in size and changed in form by the wearing 

 of shoes. Also, it is stated by medical authorities 

 that the wearing of corsets changes the shape of 

 the ribs. In these two cases it is not necessary 

 that the pressure be great enough to be uncomfort- 

 able, and during the periods of sleep the pressure 

 is entirely removed. This shows that, in order to 

 change the shape of bones, the pressure need not 

 be constant, if it be only long continued each time, 

 and active the greater part of the time. The pres- 

 sure of the tendons, nerves, arteries, muscles, etc., 

 upon the bones must also have its effect upon the 

 shape of the latter. The strain, or pulling of the 

 muscles, ligaments, etc., upon the bones must pro- 

 duce a great effect. This is shown by the ridges 

 caused by the insertion of the muscles, and by the 

 long projections of bones where great tendons are 

 inserted. As pressure on a bone, at any spot, pre- 

 vents growth at that spot, so strain or pull seems to 

 induce growth ; though, where there is a constant 

 changing in the direction of the pull, the varying 

 effects would tend to be neutralised, and, therefore, 



