128 



THE OSTEOLOGY OF THE REPTILES 



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. loi) 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, some- 

 times coossified with each other; nor are they expanded mesially in 

 either the Phytosauria or Choristodera (Fig. 104), and all water rep- 

 tiles. Doubtful vestiges of the clavicles have been reported in the 

 pterodactyls. 



