PARIETAL FORAMEN OF REPTILES 269 



when this is present would have probably acted as a contributory factor 

 in the final obliteration of the parietal foramen and its contents. 



In some cases in which a " parietal eye " is absent, a parietal foramen 

 is nevertheless present in the cartilaginous roof of the embryonic skull. 



Fig. 191. — Dorsal View of Skull of Mixosaurus atavus, from the Trias, 

 Germany, showing the Parietal Foramen, lying between the Temporal 

 Fossae and at the Junction of the Parietal with the Frontal Bones. 

 (After F. V. Heune.) 



Immediately beneath and partially occupying the foramen are the distal 

 ends of the paraphysis, dorsal sac, and the end vesicle of the pineal organ, 

 as shown in an example of a 33-mm. embryo of Platydactylus muralis, 

 described and figured by Melchers (1899). The foramen is, however, 

 usually absent, at any rate in the adult animal in those cases in which no 

 parietal eye is developed, e.g. Gecko verus. 



