Page:The Osteology of the Reptiles.pdf/176

158

The humerus (Figs. 129–131), or first bone of the anterior extremity, articulates in the glenoid fossa of the scapular girdle, usually by a more or less complete, free, ball-and-socket joint, permitting rotation. In most of the Cotylosauria (Figs. 128, 130, 132) and stouter-limbed Theromorpha (Figs. 129, 131, 134) the articular surface is more or less spiral-like, extending around the head from the ventral postaxial to the dorsal preaxial side, permitting movement in an antero-posterior direction with a concomitant partial rotation as the hand, directed forward obliquely, is brought backward in walking. The bone was not depressible below a horizontal plane without dislocation. The articular surface of the pterodactyl humerus