Page:The Osteology of the Reptiles.pdf/151

Fig. 106. Dimetrodon (Theromorpha): scapula (sc), coracoid (cor), and metacoracoid (mcor).

It is probable that the three bones early acquired a firm union, both ontogenetically and geologically, and that there was a progressive separation and delayed ossification of the posterior bone in the line leading toward the modern reptiles at least. It is known that in Ophiacodon from the Permocarboniferous, ossification of the metacoracoid 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 Rhynchocephalia. Paleontological evidence that it is the posterior bone