344 KANSAS UNIVERSITY SCIENCE BULLETIN. 



small, raised tubercle, which has a small facet for the articula- 

 tion with palatine. 



Articulations. 



The prefrontal articulates with the ethmoid by two articula- 

 tions, making a large foramen between the two. It articulates 

 with the other prefrontal on the median line. The inner face 

 is very irregular. The outer edge of the dorsal part articu- 

 lates with the suborbital ring. Posteriorly it articulates with 

 the pterygoid, and on the inner ventral edge it has a slight ar- 

 ticulation with the vomer. The palatine fits on a slight tubercle 

 which has a small facet ; this is on the ventral part. The dorsal 

 part of the prefrontal forms the anterior part of the orbit. 



Ethmoid. (Plate XXV, Eth. plate XXVI, plate XXVII, Eth. plate 



XXXIII, figs. 42, 43, 44.) 



The ethmoid is wedge-shaped, with the antero-ventral part 

 drawn down ventrally. It articulates with the frontal by fitting 

 into a cavity in the anterior end. 



Anterior Face. (Plate XXXIII, fig. 44.) 



The face is divided by a sharp ridge extending dorso-ven- 

 trally through its median line, making two concave surfaces, 

 one on each side, which articulate with the premaxillse. The 

 lateral edges are drawn out laterally, forming two small wings, 

 their ventral edge being a little below the center of the bone. 

 Below these wings this face slopes rapidly posteriorly. A dor- 

 sal view of the ethmoid shows a kite-shaped outline. The dor- 

 sal surface is rather flat anteriorly for about one-third of its 

 length, where it becomes sharp and keeled on the dorsal edge. 

 The whole bone is compressed laterally, the dorsal edge having 

 a prominent keel occupying its middle third. 



Posterior. 



A posterior view shows the upper part to be rather cone- 

 shaped — a cone rounded at the ventral edge and sharp on the 

 dorsal edge. At the ventral anterior part it has two articu- 

 lating surfaces. 



Articulations. 



The ethmoid has five : Anteriorly with the two premaxillse ; 

 posteriorly with the frontal, by the cone-shaped part being 

 sheathed in this bone ; on the postero-ventral face with the two 

 prefrontals and parasphenoid ; ventrally with the vomer. 



