CHAPTER IX
THE SUBCLASS SYNAPSIDA
A single, lateral, temporal opening, bounded primarily by the squamosal, jugal, and postorbital only. About seven cervical vertebrae, amphicoelous. Dorsal ribs double-headed, articulating intercentrally more or less and with the arch. Pectoral girdle with two coracoids on each side, sometimes with vestigial cleithrum; interclavicle and clavicles always present. Pelvis more or less plate-like. Feet always pentadactylate.
Fig. 164 bis. Sphenacodon (Theromorpha). Restored skeleton.
4. ORDER THEROMORPHA
Vertebrae notochordal or deeply biconcave, the intercentra persistent throughout. Limbs and palate primitive. Propodials in locomotion horizontal.
There has been much discussion as to the rank and limits of the Paleozoic genera included under the above definition. Nor can we hope to reach a very satisfactory solution of the numerous problems till much more is known of them and especially of the later Permian and Triassic forms included here in the same subclass.
The above definition will distinguish fairly well the Lower Permian forms from the Middle and Upper ones, and the order Theromorpha may be therefore accepted for the present with these limitations. Originally the name was proposed by Cope to include not only the Cotylosauria but all of the African genera of the order Therapsida as
