THE PECTORAL AND PELVIC GIRDLES 135 



clavicles, originally pierced by the coracoid foramen, primitively 

 forming at least the front part of the glenoid, often articulating with 

 the sternum. 



"(c) The metacoracoid of Permian reptiles, originally forming 

 the back part of the glenoid region, lost in later reptiles (Williston), 

 and in mammals except when preserved as a vestigial element." 



It is true that such an element as the epicoracoid has not been 

 found ossified in the early reptiles, but neither have numerous 

 other bones in the mesenchyme of mammals, and its ossification in 

 mammals would be nothing remarkable. A comparison of the epi- 

 coracoid of lizards (Fig. 99 b) with that of monotremes will show 

 their identity in relations. And doubtless a similar epicoracoid filled 

 in the interval between the coracoids above the clavicles and inter- 

 clavicles in the early reptiles (Fig. 96 d). Should it eventually result 

 that Broom's theory is the correct one, that both coracoids have re- 

 mained in the Monotremata, the posterior one of which presumably 

 represents the chief ossification of the coracoid process of higher 

 mammals, then modern reptiles have no true coracoid, and the bone 

 so called must be known as the procoracoid. The author believes 

 that Gregory's theory is more probable. But, until the real homol- 

 ogies are fully determined, and to save confusion for the present, the 

 terms procoracoid for the anterior bone, metacoracoid for the pos- 

 terior are adopted in this work. 



In all known reptiles possessing a metacoracoid, the suture sepa- 

 rating it from the procoracoid enters the glenoid fossa (Fig. 106), ex- 

 cept in certain therapsids (Fig. 107), where it jcins the scapular 

 suture a little in front of the articular surface. It passes directly in- 

 ward to terminate in the free border. The scapula-procoracoid 

 suture, in all the Cotylosauria and Theromorpha (Fig. 106) at least, 

 divides nearly equally the glenoid surface in front of the meta- 

 coracoid, and is thence directed forward and upward to terminate 

 in the front border. 



The supracoracoid foramen, always present in the procoracoid 

 (Figs. 95, 96, 99, 100, 106, 107), though not in the epicoracoid of the 

 monotremes, and usually present in the coracoid of later reptiles 

 (Figs. 112, 113), is absent in the Chelonia (except the Triassic Stego- 

 chelys), the Pterosauria, Ichthyosauria, Plesiosauria, Rhynchosau- 

 ria {Howesia), many Phytosauria, and the Thalattosauria — chiefly 



