Pineal Eye in Extinct Vertebrates. 917 
fering with the respiration. The characters of the brain are as 
follows: 
The first point which arrests the attention in making a compari- 
son with Diadectes is the similarly huge size of the epiphysis in the 
two types. A foramen on each side of the base of the epiphysis in 
the Diadectes gave exit to a process similar to that which enters the 
orbitopineal canal in the Belodon, and which I called the lateral 
process of the epiphysis in the latter. Plate XVIII, figs. 1-3, 1 f). 
_ The processes are probably homologous in the two genera, but in 
the Belodon they extend through the posterior wall of the orbit, fill- 
ing a large canal. There is little resemblance between the two 
brains in other respects, but they agree in the small size of 
the prosencephalon, and in the complete enclosure of the rhinen- 
cephalon by osseous walls. In the Diadectes there is no optic 
foramen, but a huge trigeminus; in Belodon, an optic foramen, 
and a very small trigeminus. 
The presence of such a huge epiphysis in the Belodon, as com- 
pared with its very small size in modern crocodiles, is a point of 
much interest, and points to its inheritance from the reptiles of the 
Permian. But if, as is probable, it contained the pineal eye, the 
latter could not receive light directly from above, since the parietal 
foramen is wanting. The presence of a communication with the 
orbit becomes interesting in this connection. A minute foramen 
passes from the base of the rhinencephalon into the orbit in the 
alligator, but the homology with the canalis orbitopinealis of Belo- 
don is by no means made out. The nervus orbitopinealis may have 
supplied the lack of light due to the closure of the parietal foramen, 
but in what way we are left to conjecture. 
The equality of size of the brain of the Belodon to that of the 
existing alligator is a point of interest. 
The Belodons were probably aquatic reptiles, living on the shores 
of estuaries like modern crocodiles, and were of carnivorous habits. 
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