ON THE STRUCTURE OF THE INNER EAR IN TWO 



PRIMITIVE REPTILES. 



E. C. CASE. 



In 1885 Cope 1 described the structure of the brain and the 

 inner ear of one of the cotylosaurian reptiles, Diadectes sp. 

 In this paper he figured the structure of the canals and con- 

 cluded as follows: "The result of this examination into the struc- 

 ture of the auditory organs in the Diadectidae may be stated as 

 follows: The semicircular canals have the structure common to 

 all the Gnathostomatous Chordata. The internal wall of the 

 vestibule remains unossified as in many of the fishes and a few 

 batrachians. There is no rudiment of the cochlea, but the 

 vestibule is produced outward and upward to the fenestra ovalis 

 in a way unknown in any other family of the vertebrates." 



Fig. i shows the arrangement of the semicircular canals as 

 given by Cope. 



Among the many specimens collected from the Brier Creek 

 Bone-bed by the University of Michigan expedition to Archer 

 County, Texas, in the summer of 1913 there are several complete 

 and nearly complete basi-cranial regions of the Permian or Permo- 

 Carboniferous reptiles, Dimetrodon and Edaphosaurus. The 

 structure of the basi-cranial region in these forms has already 

 been described by the author, 2 but the recovery of this new 

 material makes it possible to describe the condition of the ear 

 cavity. 



The specimen of Edaphosaurus, No. 3446 University of 

 Michigan, probably belongs to the species cruciger of Cope. 

 The bones of the ear region are undistorted and the cavity shares 

 in the perfection of preservation. This is shown by the complete 

 correspondence of the two sides and by the similarity of the 

 cavity to that in less perfectly preserved specimens. If the co- 



1 Cope, Proc. Am. Phil. Soc., p. 234, 1885. 



- Case, Publication 55, Carnegie Institute of Washington, p. 98, 1907. Williston 

 and Case, Publication 181, Carnegie Institution of Washington, p. 81, 1912. 



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