STRUCTURE OF INNER EAR IN REPTILES. 



21. 



lagena and shows no evidence of any curvature; the second 

 extension is smaller and connected with the lagena cavity, it 

 can only be for a considerable remnant of the sacculus. 



The inner wall of the otic cavity was incomplete and the 

 fenestra ovalis opened about opposite the upper end of the lagena. 



The second specimen, No. 3447 University of Michigan, is that 

 of one of the smaller but undeterminable species of Dimetrodon. 

 It is as well preserved as that of the Edaphosaurus, both sides 

 being present and identical in appearance and the details of 

 the structure further verified by other specimens. The general 

 arrangement of the canals and cavities is the same as in Edapho- 

 saurus but it is smaller. The evidence for the presence of a 



FIG. 3. 



FIG. 4. 



FIG. 3. Outline of the canals of the right side in Edaphosaurus. ac, anterior 

 canal; ass, apex of the sinus urticule posterior; pc, posterior canal; pa, posterior 

 ampulla; 5, sacculus; /, lagena; et, external canal; ut, utriculus; aa, anterior ampulla. 



X 2. 



FIG. 4. Outline of the canals of the right side in Dimetrodon sp. 

 same as in Fig. 3. X 2. 



Lettering the 



apex of the sinus utriculus superior js less pronounced than in 

 the first specimen but there can be no doubt of its presence. 

 The two lower cavities, for the lagena and the sacculus, are 

 narrower and in less open connection. The arrangement of the 

 canals is shown in Fig. 4. 



The author is unable to bring the structure as here made out 

 into adjustment with the figures given by Cope for Diadectes. 

 In comparing the structure of the inner ear of these primitive 

 forms with that of modern reptiles certain archaic characters are 

 recognized. The presence of an apex to the sinus utriculus 

 superior is notably primitive, Retzius shows it as present in 

 certain fishes but it is not noted in the amphibians and reptiles. 



