22 ANIMAL MECHANICS 



kind, to connect the bones, they are, still, securely 

 joined, and it requires his art to burst them asun- 

 der ; and for this purpose he must employ a force 

 which shall produce a uniform pressure from the 

 centre outwards ; and all the sutures must receive 

 the pressure at one time and equally, or they will 

 not give way. And now is the time to observe 

 another circumstance, which calls for our admira- 

 tion. So little of accident is there in the joining 

 of the bones, that the edge of a bone at the suture 

 lies over the adjoining bone at one part and under 

 it at another, which, with the dovetailing of the 

 suture, as before described, holds each bone in its 

 place firmly attached ; and it is this which gives 

 security to the dome of the cranium. 



If we look at the skull in front, we may con- 

 sider the orbits of the eye as crypts under the 

 greater building. And these under-arches are 

 groined, that is to say, there are strong arched 

 spines of bone, which give strength sufficient to 

 permit the interstices of the groinings, if I may 

 so term them, to be very thin. Betwixt the eye 

 and the brain, the bone is as thin as parchment ; 

 but if the anterior part of the skull had to rest on 

 this, the foundation would be insufficient. This 

 is the purpose of the strong ridge of bone which 

 runs up like a buttress from the temple to the 

 lateral part of the frontal bone, whilst the arch 

 forming the upper part of the orbit is very strong : 



