NO. 1660. 



OSTEOLOGY OF CAMPT08AVRU8—GILM0RE. 



247 



THE SHOULDER GIRDLE. 



The scapula and coracoid are the only elements preserved in the 

 pectoral arch. Nothing representing either a clavicle or a sternal 

 has j'-et been found, although it appears quite probable, as will be 

 shown later, that such may have been present, notwithstanding 

 Marsh's statement that the sternum in Camptosavrus was unossified. 



TJu' scapula. — The scapula is a moderately long bone, and when 

 not flattened by crushing has a decided bow in the shaft which con- 

 forms closely with the outward curve of the body cavity (see fig. 22), 

 and which throws the articulated coracoid 

 well in under the chest. Just above the 

 heavy, expanded articular end the shaft con- 

 tracts rapidly, but again gradually expands 

 antero-posteriorly toward the upper end. 

 The backward extension of the blade being 

 the greater, the median external portion of 

 the hhaft is gently rounded transversely, 

 while the thin expanded upper extremity of 

 the blade is quite flat. The upper end termi- 

 nates as a slightly thickened rounded border. 

 The anterior border is sinuous and has a 

 sharp edge, while the posterior is rounded 

 except in its upper third, which is compara- 

 tively thin and sharp. The internal sur- 

 face is smooth and flattened, with a decided 

 bow from end to end, as mentioned above. 

 The articular end being expanded both ver- 

 tically and transversely, is heav}^ and mas- 

 sive. A prominent ridge is developed on the 

 loAver outer surface, which contributes to the 

 formation of the posterior lip of the glenoid 

 fossa (see ^, fig. 23). On the anterior mar- 

 gin, above the articulation for the coracoid, 

 is a strong protuberance with a well-defined 

 triangular facet, adapted to the support of 

 a clavicle, if such a bone were present. This feature is clearly shown 

 in the right scapula of Xo. 5473, U.S.N.M., and is also seen in other 

 scapula^ in the same collection. A somewhat similar protuberance is 

 noticed on the scajDula^ of the larger trachodonts. A short but promi- 

 nent ridge rises on the external face of the projection just described, 

 but graduall}^ subsides upon reaching the flattened surface of the 

 shaft. The articular end presents a thickened, roughened, deeply 

 pitted sutural articulation for the coracoid, with which it has never 

 yet been found firmly coossified. Inferiorly and posterior to this 

 border is a smooth, concave articular surface which, with a similar 

 surface on the coracoid. forms the glenoid fossa. 



Pig. 22. — Posterior view 

 of articulated scapula 



AND CORACOID OP CaXIP- 

 TOSAURUS DISPAR MaKSH. 



Cat. No. 5473, U.S.N.M. ; 



J NAT. SIZE ; C, CORACOID ; 



yl, glenoid CAVITY ; s, 

 SCAPULA. From a photo- 

 graph. 



