THE MOST PRIMITIVE KNOWN REPTILE. 



273 



triangular space between this facet on the ptei'ygoid and that on 

 the basipterygoid process with which in ordinary reptiles it 

 should articulate. In Munich B, this space is filled up by a 

 small separate bone on the right side of the skull. The fact that 

 although in A this bone is not preserved, the facets on the 

 pterygoids and basi pterygoids are identical in the two specimens, 

 shows beyond dispute that it is a separate bone. Nothing similar 

 is known in any other Tetrapod. 



Text-fiffure 5. 



Seymouria hayloriensis Broili. — Palate, X |. Drawn from Munich B. 

 Reference letters as before with : — Pae.Sp., pavasphenoid. 



In advance oi the quadrate ramus the pterygoid is represented 

 by a lai'ge flat bone in the palate which articulates with its 

 fellow in the middle line in advance of the parasphenoid, and 

 laterally has sutures with the transverse, palatine, and prevomer. 

 That margin of the palatal part of the pterygoid which forms the 

 anterior limit of the subtemporal fossa is slightly deflected 

 laterally, so that with the ectopterygoid it forms a small flange 

 against the inner surface of the lower jaw. 



Ectopterygoidj. — The ectopterygoid is a bone of few features. 

 It forms merely a plate in the palate articulating with the 

 pterygoid in a suture only shown incompletely in my skull, a 

 long suture with the palatine and presumably another with the 

 maxilla. About the middle of its area in Munich A is a small 

 depression probably intended to receive a tooth on the lower 



Palatine. — The palatine is well shown in Munich A and in my 



