THE SKELETON IN AMPHIBIA. THE HYOID. 



181 



The dorsal parts of the first three branchial arches disappear, 

 but those of the fourth become ossified and form the short, 

 stout thyrohyals or posterior cornua. The dorsal parts of the 

 hyoid arch in the adult form a pair of long bars, the anterior 



FIG. 29. VISCERAL ARCHES OF AMPHIBIA. 



A. Molge cristata (after PARKER). 



B. Rana temporaria adult (after PARKER). 



C. Tadpole of Rana (after MARTIN ST ANGE). 



D. Siredon pisciformis (after CREDNER). 



In each case the ossified portions are slightly shaded, while the carti- 

 laginous portions are left white. 



1. basilingual plate. 



2. hyoid arch. 



3. first branchial arch. 



4. second do. 



5. third branchial arch. 



6. fourth do. 



7. tbyrohyal. 



8. copula. 



