112 NOTES TO THE 



of the above-mentioned plates of bones, with denticulated 

 edges, &c. ; while the centre portion of the bone sends down an 

 arch to form a canal in which the spinal marrow is contained. 



The tortoise therefore lives inside a house which is composed 

 of his own ribs, formed into a dome, and he rests upon his 

 sternum or breast-bone, which is flattened out into a broad 

 plate to serve, first, for the attachment of the rib, and second, 

 as a kind of supporting foot or basement. Can there possibly 

 be a more beautiful piece of design than this, which combines 

 economy of material and great strength with lightness ? 



We often find the same design in created things utilised for 

 various purposes. It is therefore highly interesting to find that 

 the same kind of denticulated suture as adopted in the tortoise 

 is present also in our own skulls. A bony box is required to 

 carry and protect the brain ; the human skull therefore is 

 formed of bones, each being joined to its neighbour by iden- 

 tically the same kind of union as that in the tortoise. There is 

 in the human skull another meaning for this : the interposition 

 of several lines of sutures all over the skull prevents a fracture 

 of one of the bones of the skull spreading to its neighbour, 

 just as the woodwork in a window-frame prevents the fracture 

 of an individual square of glass spreading to the adjoining 

 squares. 



STRUCTURE OF A Cow's HORN, p. 136. It is often the case that 

 in the commonest objectswe maysee (if we like) beautiful examples 

 of engineering structures. I take the anatomy of the cow's 

 horn as a good example. In the summer of 1874, 1 was inspecting 

 the large tanneries of the Messrs. Hamlyn, at Buckfastleigh, on 

 the Eiver Dart, Devonshire, to see if any injury was happening 

 therefrom to the salmon fisheries. In one of the backyards was 

 a mountain of the skulls and horns of cows of all sorts and 

 kinds. Here there was a treasure worthy of investigation ; so I 

 got on to the mountain of horns and skulls, and picked out some 

 beautiful specimens, in order to make sections, &c. 



I find that over the brain of the cow a strong roof of bone is 

 thrown, in the shape of an arch, so as to form a substantial 

 foundation for the horns. This roof is not solid, but is again 

 strengthened below by a series of bony arches, that are so dis- 

 tributed as to form a series of hollow chambers, thus forming a 

 structure uniting strength with lightness. The problem now is, 

 how to fasten the horn on each side on to this buttress. The horn 

 itself must of course be formed of horn proper, i.e., hardened 

 hair. In the rhinoceros we find a horn composed entirely of a 

 solid mass of what is really a bunch of hair agglutinated together; 



