340 KANSAS UNIVERSITY SCIENCE BULLETIN. 



A small groove for the opisthotic is seen close to the inner edge 

 of the face. 



Articulations. 



Considering it separately, the pterotic has seven articula- 

 tions. It articulates with the parietal dorsally ; anteriorly with 

 the sphenotic and epiotic on its inner posterior face; ventrally 

 with the exoccipital, prootic and hyomandibular. 



Sphenotic. (Plates XXV, XXVI, XXVII; Sph. Plate XXXIII, figs. 46, 



47, 48; plate XXIX, fig. 11.) 



The sphenotic extends out farther laterally than any other 

 bone in the skull. It is posterior to the frontal and alisphenoid 

 and extends outward and backward. It is hexagonal in shape. 

 The posterior edge is parallel to the long axis of the skull and 

 its posterior edge is at right angles to the long axis, and its 

 lower edge extends anteriorly and superiorly, narrowing down 

 to a blunt point. It has three faces, an outer, inner and pos- 

 terior. 



Outer Face. (Plate XXXIII, fig. 46.) 



The outer face is smooth, concave from the posterior to the 

 anterior edge and convex from the superior to the inferior 

 edge. The posterior part is almost at right angles to the an- 

 terior, as the bone inclines outward, thus making the posterior 

 face. The posterior edge is drawn out into a sharp ridge, 

 making the posterior face a long groove, wide at the inferior 

 part and narrowing rapidly at the superior portion. The lower 

 part points downward and backward and forms the greater 

 part of the pit for the hyomandibular, the prootic forming the 

 rest of the cavity. 



Injier Face. (Plate XXIX, fig. 11; plate XXXIII, fig. 48.) 



The inner face forms a part of the brain-case and is about 

 three times as long as wide, and is narrowed down to the an- 

 terior end and rounded posteriorly. There is a tongue on the 

 middle of the ventral edge which fits into a groove on the 

 prootic. This face is slightly concave, and is built up above the 

 rest of the bone. It has a prominent depression at the posterior 

 part. All of the bone forming a part of the brain-case is pitted 

 and honeycombed. 



A7•tic^llations. 



The sphenotic has six articulations. Anteriorly it fits into a 

 notch on the posterior part of the frontal; the antero-ventral 



