Page:Geology and Mineralogy considered with reference to Natural Theology, 1837, volume 1.djvu/142

 138 of bony plates, was to give strength to the surface of so large an eye-ball, enabling it the better to resist the pressure of deep water, to which it must often have been exposed; it would also have protected this important organ from injury by the waves of the sea, to which an eye, sometimes larger than a man's head, must frequently have been subject, when the nose was brought to the surface, for the necessary purpose of breathing air: the position of the nostrils, close to the anterior angle of the eye, rendered it impossible for the Ichthyosaurus to breathe without raising its eye to the surface of the water.

The Jaws of the Ichthyosauri, like those of Crocodiles and Lizards, which are all more or less elongated into projecting beaks, are composed of many thin plates, so arranged as to combine strength with elasticity and lightness, in a greater degree than could have been effected by single bones, like those in the jaws of Mammalia. It is obvious that an under jaw so slender, and so much elongated as that of a Crocodile or Ichthyosaurus, and employed in seizing and retaining the large and powerful animals which formed their prey, would have been comparatively weak and liable to fracture if composed of a single bone. Each side of the lower jaw was therefore made up of six separate pieces, set together in a manner that will be best understood by reference to the Figures in Pl. 11.