MEDIAN EYES IN EXTINCT VERTEBRATES 



339 



sentatives of the Crossopterygian fishes, it will be necessary to consider 

 the relations of the Cyclostomata to the fossil representatives of this 

 order, and in particular to the Anaspida, Cephalaspida, and Palaeospondy- 

 lus. We have already seen that in amphibians and reptiles the pineal 

 system attained a maximum development in the extinct Labyrinthodonts 



Fig. 237. — Reconstruction of Skull of Titanosuchus, a Mammal-like 

 Reptile of S. Africa. (After D. M. Watson.) 



The specimen shows a large parietal canal for the pineal organ, " the walls 

 of which form a special little projection raising the opening more than a centimetre 

 above the general line of the surrounding bone." 



A — Dorsal aspect of skull. B — Posterior aspect. C — Lateral aspect. 



/. PAR : interparietal. SQ. : squamosal. 



PC. : parietal canal. TAB. : tabulare. 



PO. : post-orbital. 



In the account of another specimen (Mormosaurus seeleyi) belonging to the 

 same order, Deinocephalia, Professor Watson describes the parietal canal as 

 " a long cylindrical tunnel " which lies in the median suture between the two 

 parietal bones. 



and in the Ichthyosauri and Plesiosauri, during the late Palaeozoic 

 (Amphibia) and the Mesozoic periods (reptiles). Many of the extinct 

 forms seem to have died out completely and left no representatives ; 

 while in the modern amphibians and reptiles the parietal sense-organ is 

 less developed and shows signs of degeneration. Similar changes appear 

 to have occurred also both generally and in the pineal system of Cyclo- 



