THE NECTURUS 11 



EXOCCIPITAL 



The exoccipitals border the foramen on all but the dorsal 

 edge. This bone is anvil shaped in posterior view. The 

 lower part of the posterior face is swollen to form the 

 lateral condyles and the articulation with the atlas. The 

 dorsal part widens out to articulate with the parietal. 

 The inner edge bears a pointed projection which articulates 

 with the parasphenoid. The outer edge articulates with 

 the opisthotio. 



Frontal 



This is a long bone, thin at the posterior end where it 

 makes a flat contact with the parietal, and irregular at the 

 anterior end. The outer, anterior edge is drawn out into 

 a process that articulates with the vomer. The ventral 

 surface has an elevated ridge or uncinate process that 

 articulates with the parasphenoid and helps in this way 

 to form the anterior, lateral wall of the brain case. The 

 two frontals, articulate with each other by a long articula- 

 tion that is about two thirds the length of the bone. The 

 posterior ends are separated by the parietals which form 

 a wedge between them. At the anterior end of the dorsal 

 face, the maxillae lie on the frontals and articulate by a 

 flat, contact articulation. 



Parietals 



The parietals are long, flat bones irregular in shape and 

 forming the dorsal part of the brain case. The dorsal face 

 has a roughened surface that forms the articulation with 

 the frontals. The anterior end divides into two parts, 

 a short part between the frontals and a larger one that 

 extends laterally over the vomer and the anterior part of 

 the chondrocranium. The dorsal face is comparatively 

 smooth. There is a long articulation between the two 



