25. For this cause too it seems to me that it has been granted a more secure defence, being distinguished, in the head, by a double shelter of bones round about, and in the vertebræ of the neck by the bulwarks formed by the projections of the spine as well as by the diversified interlacings of the very form of those vertebræ, by which it is kept in freedom from all harm, enjoying safety by the defence that surrounds it.