

THE HUMAN SKELETON. 71 



and the fibres of the two bones are thus interlaced, as you 

 might interlace your fingers. But f this dove-tailing exists 

 only in the external plate^ on the internal surface the bones 

 are simply laid in contact. 



17. Sir Charles Bell compares the human skull to the 

 dome of a building, which is acknowledged to be one of 

 the most difficult pieces of architecture. The dome of St. 

 Sophia, in Constantinople, built in the time of the Emperor 

 Justinian, fell three times during its erection ; and the dome 

 of the Cathedral of Florence, stood unfinished 120 years for 

 want of an architect. " Yet," says this writer, " we may, 

 in one sense say, that every builder who tried it, as well as 

 every labourer employed, had the most perfect model in his 

 own head." The difficulty in constructing a dome, is the 

 tendency of the weight of its upper part, to disengage the 

 stones from each other which form the lower circle, and 

 crowd out the circular wall on which it rests. This is 

 guarded against, either by soldering the stones into each 

 other, or by hooping them together by strong iron hoops. 

 The dome of St. Paul's, in London, is secured by several 

 strong double iron chains, linked together at the bottom and 

 along the sides of the cone. Now, In the bones which com- 

 pose the dome of the cranium, we find the edge of a bone at 

 the suture lying over the adjoining bone at one part .and 

 under it at another ; which, with the dove-tailing above- 

 mentioned, holds each bone securely in its placej But while 

 a dome is calculated to resist one kind of force, viz. that 

 acting perpendicularly, or in the direction of gravity, the 

 skull is equally calculated to resist forces operating in all 

 directions. Thus it can be shown, that no other form of 

 equal strength could be devised. When we reflect on the 

 strength displayed by the arched film of an egg-shell, we 

 need not wonder at the severity of blows which the cranium 

 can withstand. 



