THE PECTORAL AND PELVIC GIRDLES 133 



It is probable that the three bones early acquired a firm union, 

 both ontogenetically and geologically, and that there was a progres- 

 sive separation and delayed ossification of the posterior bone in the 



Fig, 106. Dimetrodon (Theromorpha): scapula {sc), coracoid {cor), 

 and metacoracoid {mcor). 



line leading toward the modern reptiles at least. It is known that in 

 Ophiacodon from the Permocarboniferous, ossification of the meta- 

 coracoid did not occur till late, and that in Varanops (Fig. 96 d) it 

 never ossified. This doubtless explains its absence in all known 

 specimens of Paleohatteria, formerly placed among the Rhyncho- 

 cephalia. Paleontological evidence that it is the posterior bone 



