214 E. C. CASE. 



ossified elements which shelter the inner ear be held in the normal 

 position, as shown in Fig. 2, it will be seen that there is the trace 

 of a groove running apparently horizontally from without 

 inward; at the inner upper corner of the cavity it joins the trace 

 of a second groove running nearly vertically. These are the 

 marks of the anterior and posterior semicircular canals and corre- 

 spond to the horizontal antero-posterior and the vertical antero- 



OP-- 



FIG. i. Outline of the canals of the inner ear of Diadectessp. From Cope, hap, 

 horizontal antero-posterior canal; aa, anterior ampulla; vap, vertical antero-pos- 

 terior canal; vl, vertical transverse canal; ap, posterior ampulla; cc, canalis com- 

 munis of the vertical antero-posterior and the vertical transverse canals; oc.os, 

 commune of the same. 



FIG. 2. Inner view of the right otic region of Edaphosaurus, showing the cavity 

 of the ear. So, supraoccipital; op, opisthotic;/w, foramen magnum. X i. 



posterior canals of Cope's figure. Where the two canals meet 

 there is a projection upward and forward of the cavity which 

 probably lodged a rudiment of the apex of the sinus utriculus 

 superior (terminology of Retzius). At the outer ends of the canal 

 there is evidence of slight enlargements which lodged the anterior 

 and posterior ampullae. Just below the point of union of the 

 two canals there is an elevation of the cavity indicating that 

 the sinus utriculus posterior was inclined inward and forward. 

 The cavity for the utriculus is relatively large and higher than 

 wide. On the outer side of the broken surface of the cavity, 

 nearly opposite the middle point there is a slight excavation 

 indicating the position of the external canal. At the lower end 

 of the cavity there are two extensions, one running into the paroc- 

 cipital (opisthotic) bone and parallel to its axis, this lodged the 



