76 CONTRIBUTIONS FROM WALKER MUSEUM 
The determination was made on a partially preserved skull of 
Dimetrodon incisivus, and a series of unfortunate conclusions have 
been drawn from this erroneous determination. ‘The present speci- 
mens show that Cope was correct in his determination of the quadrate 
as an elevated bone, and also demonstrates its remarkable similarity 
in position and relations to the quadrate of Sphenodon. 
Figs. 1, 2, and 4 show the general form and relation of the quad- 
rate. It is an elevated, thin plate of bone ending freely above, articu- 
Fic. 1.—Left side of the skull of Dimetrodon gigas. About one-fourth natural 
size. Full length of skull, 46m. 
lating with the pterygoid anteriorly, and the quadrato-jugal, squamosal 
and paroccipital posteriorly. The lower end is terminated by two 
elongate articular condyles, which run almost parallel antero-posteri- 
orly, but are slightly convergent anteriorly. The inner condyle 
stands out from the side of the bone, and its inner side articulates 
with the posterior end of the pterygoid. The outer condyle projects 
beyond the posterior edge of the bone, and its upper surface is flat, 
forming a sort of shelf, to the upper side of which is articulated the 
lower end of the quadrato-jugal. 
The quadrato-jugal is a very slender plate of bone that articulates 
with the posterior edge of the quadrate for its full length. Above, the 
quadrato-jugal passes between the squamosal and prosquamosal, and 
articulates with the parietal; below, it is separated from the quadrate 
by a fair-sized quadrate foramen. 
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