THE PLASTRON OF THE CHELONIA . 



115 



and the two epi2:>lastra correspond with the median and lateral 

 thoracic plates of the Labyrinthodont Amphibia, and very 

 probably answer to the interclavicle and clavicles of other 

 Vertebrata. 



FiQ. 64. — The plastron of the Green Turtle (Chelone midax): T.cl, interclavicle; cL clavi- 

 cles ; IIi/p., hyoijListron ; ///J-i?., hypoplustroa ; Xp.^ xiphiplastron. 



The sacrum consists of two vertebra?. The expanded 

 sacral ribs are not anchylosed with the centra and arches of 

 their vertebrae. 



The tail is flexible, and consists of procoelous vertebr.'e. 



Fig. 65. — ^External view of a section of the auditory re^'on of the skull in a Turtle {Ofielant 

 midas)\f. o., fenestra ovalis;/'. r., fenestra rotunda; esc, a^c, pse, external, anterior, 

 and posterior semicircular canals. 



