OOAL-MEASURE STEQOCEPHALIAX. 955 



the interclavicle which overlaid it, and enables the width of the 

 latter bone to be accurately determined. 



Text-%. 167. 



Ceraterpeton retictdatum H. & A. Restored dorsal surface of skull and 

 clavicular arch. X 4. 



The cleithrum is a T-shaped bone, flat, and ornamented by 

 fine grooves, the upright of the T is affixed to the vertical process 

 of the clavicle. 



Discussion of the Skidl. 



One of the most interesting features of the skull is the reduc- 

 tion of the number of bones in the temporal region. The 

 primitive amphibian has in the temporal region three bones, the 

 squamosal, supratemporal, and intertemporal, all of which occur 

 in the primitive reptile Seymouria. It is important to discover 

 which of these bones is really present in BatracMderjyeton. 



In the primitive amphibians ^^ Loxomma" and Pterojdax all 

 three bones are present in a typical manner and also the 

 squamosal ; that is, the outer bone, which articulates with 

 the quadrato-jugal, is well characterized and differentiated from 

 the other two by the fact that its postei-ior border is bent down 

 in front of the otic notch and articulates with the upper edge of 

 the quadrate ramus of the pter3'goid, it also passes down behind 

 the quadrate itself, overlapping a good deal of its posterior 

 surface. Neither the intertemporal nor supratemporal has any 

 connection whatever with the pterygoid or quadrate. 



The conditions in these primitive amphibia are those which 



