No. 374.] THE PRIMITIVE REPTILIA. 71 
the body, the tarsus, abdominal ossicles, and distal end of the 
humerus, gave rise to the Rhyncocephalia. The temporal regions 
of Proganosauria and Rhynco- 
cephalia are very similar, the 
only difference being that in 
the first order the squamosal 
and prosquamosal are separ- 
ate, while in Sphenodon, a typi- 
cal rhyncocephalian, they are 
united. The condition of this 
region in the two forms is in- 
dicated in Fig. I. Fic. 1. — TEMPORAL REGION OF THE 
Before the development of a io et epi 
the Rhyncocephalia, however, ~’ citi ©, oMa oy AEA 
there appeared among the early s ‘squamo zig 
Permian reptiles forms which 
exhibited the first steps in one 
of the most profound mutations 
of the reptilian line. These 
forms show a flattened form 
of quadrate instead of the 
elongated form of previous 
orders. It has been shown 
FIG, 2. hanged RAL REGION OF THE 
by Baur and the author (4) that SKULL oF DIMETRODON. 
the Pelycosauria of Cope are  Ą frontal; of, postfrontal. Other lettering 
very similar in structure to Se. ae 
the Rhyncocephalia, differing chiefly in the flattened quadrate. 
The difference in the temporal region of these forms from that 
of the Rhyncocephalia can be readily seen by comparing Fig. 2 
with Fig. 1. 
In the paper just cited, page 113, the authors stated that they 
considered the Pelycosauria “a specialized side branch of a line 
leading from the Proganosauria to the Rhyncocephalia.” The 
author is now inclined to attach much greater importance to 
the appearance of the flattened quadrate at this point. The 
Pelycosauria and many of the:Permian forms from South 
Africa and Russia all show this character of a depressed 
quadrate more or less completely surrounded by the supporting 
