CHAPTER IX 



THE SUBCLASS SYNAPSIDA 



A SINGLE, lateral, temporal opening, bounded primarily by the squa- 

 mosal, jugal, and postorbital only. About seven cervical vertebrae, 

 amphicoelous. Dorsal ribs double-headed, articulating intercen- 

 trally more or less and with the arch. Pectoral girdle with two cora- 

 coids on each side, sometimes with vestigial cleithrum; interclavicle 

 and clavicles always present. Pelvis more or less plate-like. Feet 

 always pentadactylate. 



Fig. 164 his. Sphenacodon (Theromorpha). Restored skeleton. 



4. ORDER THEROMORPHA 



Vertebrae notochordal or deeply biconcave, the intercentra per- 

 sistent throughout. Limbs and palate primitive. Propodials in loco- 

 motion 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 



