the end of the interclavicle; and a more or less slender stem which articulates with the front border of the scapula, or its acromion when present, and also with the lower end of the cleithrum when that bone is present. In modern lizards the clavicles articulate usually with the front border of the cartilaginous suprascapula (Fig. 99). The inner end in some lizards is broad and perforated (Fig. 99 c).
Fig. 98. Edaphosaurus novomexicanus (Theromorpha). Pectoral girdle, two fifths natural size: c, cleithrum; cl, clavicle; sc, scapula.
The clavicles of the Chelonia are known as the epiplastra of the plastron (Fig. 100). In the Nothosauria (Fig. 101) they are normal but very stout, firmly united with the scapula and with each other. The clavicles of the Plesiosauria (Fig. 102) are remarkable in some respects. Usually they are a pair of thin, triangular bones, lying upon the inner or visceral surface of the proscapular process of the scapula (corresponding to an acromion), of the interclavicle and sometimes also of an anterior process from the coracoid; they may be absent. In the Ichthyosauria (Fig. 103), they are slender, sometimes coössified with each other; nor are they expanded mesially in either the Phytosauria or Choristodera (Fig. 104), and all water reptiles. Doubtful vestiges of the clavicles have been reported in the pterodactyls.
