70 PHYSIOLOGY. 



a, the external, 6, c, the internal table ; the intermediate cellular 

 texture, being soft and spongy, and conveying vessels and nerves from 

 one part to another. 



15. It is worthy of particular remark, how the changes 

 in the structure of the bones of the skull are adapted to the 

 changes in the mind at different periods of life. /At birth, 

 the skull is soft and yielding, there being considerable inter- 

 vals between the adjacent bones of which it is composed ; 

 during childhood, it is highly elastic, so that the heedlessness 

 of that period may not endanger concussion, to which it is 

 so often exposed from falls ; and during youth and up to 

 manhood, the parts which are exposed to the contact of ex- 

 ternal bodies, are thicker, and the bones are still not firmly 

 consolidated at their sutures or seams, by which they are 

 united. As old age approaches, man grows more timid, and 

 is little disposed to feats of agility or activity ; something 

 teaches him that falls or blows, which could once be borne 

 with impunity, can no longer be encountered with safety ; 

 and if we examine the skull, we find the two layers of bone 

 consolidated into one. The result of which is, that con- 

 cussion at this period would be far more dangerous than in 

 early life, or at the age of manhood. 



16. The sutures, or joinings of the bones of the skull, in- 

 terrupts, in a measure, the shock of the vibration produced 

 by external violence, and also prevent fractures from extend- 

 ing as far as they otherwise would do, in ofl'e continued bony 

 substance/ No one can examine the joinings of two of the 

 bones of the cranium, without admiring the minute dove- 

 tailing by which one portion of the bone is inserted into, 

 and surrounded by the other, whilst that other pushes its 

 processes out between those of the first in the same manner ; 



