466 



Annals of the Carnegie Museum. 



thyro-hyals, there is evidence of the attachment of cerato-hyals, or of 

 ligaments connecting with or having the function of these bones. 

 They are, however, missing in the specimen. 



Fig. 4. Anterior view of hyoid bone of iMastodon Anteruatitis Kerr, 

 hyal bone; 77/, thyro-hyal bones. i^]\ nat. size.) 



BIl, basi- 



The Thyro-Jiyal Bones (Figs. 3, 4, 5). — The extreme length of 

 these bones from their symphyses with the basi-hyal to their upper 

 extremities is 18.75 cm. Their width at the point of union with the 

 basi-hyal is 5.10 cm., and at the middle of the shafts is only 2.85 

 cm. They again widen at their upper extremities to 4.30 cm. The 

 thickness of the shaft at the middle is only i cm. The bones are 

 flattened on their outer surfaces, laterally convex inwardly, and the 

 anterior margin near the upper extremity is twisted and flares out- 

 wardly. The anterior margin is approximately straight until near the 

 upper end, when it curves rapidly backward. The posterior margin 

 is gently concave. At the point of union with the basi-hyal the bone 

 is greatly thickened. 



Evidences of the usual muscular attachments are found everywhere 

 upon the antero-superior surfaces of the bones. 



The mastodon evidently was i)rovided with powerful vocal organs. 



