PECTORAL GIRDLE REPTILES 25 1 



coracoid fenestra. This interpretation, however, meets some 

 difficulties. 



The clavicle extends transversely, in front of the fenestra, from 

 scapula towards the median hne, and may meet its fellow. Its 

 medial end is often broad, these enlargements sometimes being 

 fenestrated (fig. 265, A, D) and resting against the sternum, the 

 anterior end of which bears a transverse bar on either side which 

 may articulate with the clavicle, or when the episternum is T-shaped 

 or cruciform, with the arm of the latter. Clavicle and sternum are 

 frequently fused for some distance. When an anterior process is 

 present the clavicle loses its connexion with the precoracoid and 

 acts as a brace between scapula and sternum. The clavicle is 

 purely a membrane bone and shows no such mixture as occurs in 

 Anura. Its extension along the anterior side of the scapula recalls 

 conditions in some fishes. The episternum is very variable in 

 shape — rhomboid, T-shaped, cruciform, or rod-like. It always lies 

 beneath the middle line of the sternum. 



In less typical lizards there is a tendency towards reduction and simplification 

 of the girdle. Heloderma and Chamceleo have a compact coracoid plate which 

 meets its fellow (Chamceleo has lost episternum and 

 clavicle), while the postero-medialb order enfolds the 

 anterior sternal margin. There is a single fenestra 

 anterior to the glenoid fossa and scapula and cora- 

 coid are continuous. In Anguis and some other 

 apodal lizards the fenestras become incisures by loss 

 of the anterior border of the coracoid region, but 

 even in Amphisbasnids and Amelia (fig. 266) rudi- 

 ments of coracoid and clavicle occur, although it is -pic. 266. — Girdle, sternum 

 difficult to say whether the former be more coracoid and ribs of a limbless lizard, 



than scapula. LepidosternonandCephaloHs are said '4«zW/« (Camp, '23). cl, 

 ^ ^ ^ clavicle; cs, coraco-scapula; 



to have lost the girdle completely. s, sternum (presternum) . 



The extinct Pythonomorphs usually lack the 

 clavicle and episternum; when present they are rudimentary. The large flat 

 coracoid has a fenestra or incisure, as well as a supracoracoid foramen. The 

 coracoids are widely separated, possibly a broad epicoracoid cartilage was 

 present. The scapula is broad triangular. 



Crocodilia. — The clavicle and precoracoid are lacking in modern 

 crocodiles but present in Pseudosudia. Crocodilus porosus has a 

 precartilage stage of a probable precoracoid. The coracoid is small 

 and expanded at either end; no incisures occur, but there is a supra- 

 coracoid foramen. The slender rod-shaped episternum joins the 



