24- RADIATED TORTOISE. 



several pyramidal areas or great triangles, whose 

 bases are about two inches broad. On the back 

 into sexangular ones, each of them convex. On 

 the sides and quite behind the shell is carried 

 somewhat inward. Before and hinderly the edges 

 are toothed, and bended outward and upward. 

 The inward edges are covered with shelly plates 

 above an inch and half broad. The concave is 

 composed of six and forty bones. Along the 

 middle of the back are twelve, all, except the 

 foremost and the four last, almost square. Next 

 to these are eight on each side, like so many con- 

 tiguous ribs ; together with two lesser square 

 bones before : next to these, eight more, as it 

 were, under-ribs, on each side. To the twelve 

 middlemost bones the ribs are joined by an alter- 

 nate commissure, so as one of them answers to 

 the halves of two ribs, and vice versa. To these 

 the under-ribs, in a wonderful manner, viz. by a 

 branched suture or indenture. For the great 

 teeth of the under-ribs being first inserted into 

 those of the upper-ribs, the indenture is afterwards 

 repeated by lesser teeth, out of the sides of the 

 great ones. Besides the most elegant ordering of 

 the work in the convex, there are three things 

 chiefly observable, which serve for the greater 

 strength of the shell. That is to say, the con- 

 vexity of the several areas on the back, the 

 branched sutures, and the alternate commissures 

 of the bones; answerable to the rule of Nature in 

 a human skull ; and of Art, in laying of stones 

 in buildings, and in covering of broader vaults, 



