164 



PICTURESQUE SKETCHES 



arranged so as to distribute in some measure the ne- 

 cessary shock arising from the convulsive jerk made 

 while the animal was in the act of seizing its prey, 

 we have this purpose effected in several of the exist- 

 ing reptiles ; but something more than this seems to 

 have been needed by the Icthyosaur, since it exhibits 

 an example of cross bracing, adding greatly to the 

 effective strength without increasing the weight. By 

 simply introducing a change of direction in the grain, 

 as it is called, or fibre of the bone, this purpose is 

 accomplished, so that the animal was enabled to 

 snap with safety at the hardest and most solid sub- 

 stance that came within its reach. The jaws of some 

 specimens must have been upwards of six feet in 

 length. 



The most remarkable peculiarities in the head of 

 this fish-reptile besides the jaws are the size and 

 structure of the eye, the smallness of the brain, the 

 separation of the different bones of which the skull is 

 made up, and the position of the nostrils. 



The orbital cavities which contained the eyes are 

 of immense size, their circumference including several 

 distinct bones (see fig. 59), and provided with plates 

 of bone partly covering the eye, and overlapping one 

 another so as to leave a variable aperture for the 

 pupil. There are instances in which these orbits 

 are eighteen inches across, or, in other words, so 

 large, that it would require a string of nearly five 

 feet long to surround the cavity of the eye. 



The eyes were placed far back on the head and 

 behind the snout, with the nostrils or breathing holes 

 just in front, so that each time that the animal came 

 to the surface to breathe, the eyes and nostrils, but 



