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Fig. 12. — Homology of the coracoid in primitive mammals 



A. Left shoulder-girdle (outer view) of an 8.5 mm. embryo of a diprotodont marsupial, 

 Trichosurus vulpecula. After Broom. In this stage the true coracoid (cf. figs, B, C) 

 is coniiected below with the sternum, as in adult monotremes. The epicoracoid ("pro- 

 coracoid" of Broom) is mesenchymatous. It does not share in the glenoid and is there- 

 fore unlike the reptilian "procoracoid"" (^coracoid), but does resemble the membranous 

 epicoracoid. 



B. Left shoulder-girdle (ventro-lateral view) of a 14.8 mm. Trichosurus vulpecula 

 embryo. After Broom. The coracoid at this stage retains its connection with the 

 sternum, which connection is lost in the adult : the epicoracoid has disappeared. 



C. Right shoulder-girdle and proximal part of humerus (inner view) of adult diproto- 

 dont marsupial. Phascolarctus ciiiereus. The single coracoid shares in the glenoid and 

 points downward and inward toward the sternum. 



D. Left scapulocoracoid ( ventromedial view) of Dasifpus sp., showing the metacora- 

 coid (m.co) as a separate element. 



E. Lower part of left scapulo-coracoid of Megatherium (inner view), after Weber, 

 showing suture between coracoid and metacoracoid. 



F. Left scapulo-coracoid of Lepus (outer and distal views), after Howes, showing 

 coracoid and metacoracoid both sharing in the glenoid articular surface. 



