92 EXTINGT MONSTERS 
Before we leave the skull there is one other very interesting 
point that should not be omitted. If the reader will refer to the 
skull of Mastodonsaurus (Fig. 16), he will see, just on the middle 
line and near the base, a small round hole. It lies over the 
brain-cavity, and most probably represents the site of a small 
third eye. Whether this little extra eye was capable of receiving 
impressions of light, and so of communicating them to the brain 
Fic. 16.—Skull of a Labyrinthodont Mastodonsaurus Jaegeri, from New Red 
Sandstone, Germany. 
as an ordinary eye does, is a matter of doubt; but in a certain 
very primitive little lizard now living in New Zealand, and 
known as the Tuatara (Sphenodon), there is a similar aperture 
overlying the rudiment of an eye now quite useless and lying 
down in the brain. This little eye in the Tuatara must at 
one time have been made use of, and the question arises 
whether the third eye of the Labyrinthodonts was similarly 
