410 tl. B POLLARD, 



The diflering Lames of homologous bones are as follows: 



Folypterus Stegocephali. 



DermalmedianEthmoid absent 



Nasale accessorium absent (? Septomaxillary, frog) 



Ant. suborbital Lachrymal 



Folypterus Stegocephali 



absent (? Os terminale) Prefrontal 



Supratemporal Supraoccipital 



(Parieto) squamosum Squamosum 



Post, suborbital Postorbital 



Posttemporal scale Epiotic (Gehördeckknochen) 



Operculum Supratemporal (Squamosum or tympanic, Uro- 



deles) 



Suboperculum Quadrato-jugal 



Preoperculum Jugal 



Jugal absent 



Through the researches of Eberhard Fraas on the Labyrinth- 

 odonts of the Trias of Swabia one can compare the back of the skull, 

 not only dermal bones but cartilage bones, of these animals with Fo- 

 lypterus and it will be seen that in essential characteristics they agree 

 remarkably. 



In Folypterus vertebrae are being drawn into the skull so that the 

 two condyles are not perceived. In the Stegocephali they are com- 

 pletely visible, which may be because, like the Amphibia, no vertebral 

 elements intrude or because as in higher vertebrates the vertebrae 

 have been completely swallowed. This appears likely because in Cyclo- 

 tosaurus there is a foramen corresponding to the hypoglossus foramen 

 in the skull. In the Stegocephali the exoccipitals do not meet in the 

 middle line above the Foramen magnum. They are continued above 

 to the supraoccipitals. In Folypterus they become connected rather 

 with the parietals from which as described above a projection runs 

 back and upwards towards the posttemporal scale. This process seems 

 to correspond with a process in Cyclotosaurus passing to the socalled 

 epiotic. 



The vagus foramen lies in these Stegocephali between the exocci- 

 pital and a process which Fraas calls exoccipitale laterale. In Masto- 

 donsaurus and Cyclotosaurus there is this curious difference that this 

 exoccii)itale laterale runs in the one up to the epiotic and there shows 

 the dividing suture while in Cyclotosaurus it meets a downward 



