94 FRANKLIN PEARCE REAGAN 



capsule. Whether the stapedial plate is to be considered a part 

 of the otic capsule, or as an independent formation in the fenes- 

 tra ovalis is purely a matter of interpretation. The greater 

 part of the stapedial plate seems to be structurally independent 

 of the otic capsule, while a portion of it is fused with the latter 

 probably from a very early time, seemingly having arisen from a 

 part of the otic capsule. It seems reasonable to assume that the 

 avian stapedial plate is not a part of the visceral skeleton. At 

 any rate, if its constituent mesenchyme is a derivative of the 

 second visceral arch, that mesenchyme is powerless to form a 

 stapedial plate unless stimulated to do so by the auditory 

 epithelium. 



It has often happened that after the seventh day the columella 

 became much flattened or irregular on its inner end. On the 

 eighth day, this internal end was often found to have fused with 

 some neighboring cartilage, sometimes with the parachordal, 

 and sometime even with the quadrate. This may conceivably 

 be an expression of its normal habit of fusing with a stapedial 

 plate. Such abnormal procedure generally necessitates a bend- 

 ing of the columella from its normal direction. This tendency to 

 fuse with neighboring cartilages seems to become even more 

 marked in later development. In one case, for which I offer no 

 explanation, the columella is bifurcated, one branch being fused 

 with the parachordal, while the other branch (fig. 10) is curved 

 dorso-laterally, its free end being connected with the external 

 auditory meatus by a column of dense prechondral mesenchyme. 



The plane of section of figure 10 on the operated side presents 

 a picture quite similar to that in figure 168 in Lillie's '^ Devel- 

 opment of the Chick." Owing to the great similarity of the 

 quadrate cartilage on the right side of my figure 10 to that car- 

 tilage which Lillie had labeled 'Meckel's' cartilage, I feel con- 

 vinced that Lillie may have misinterpreted the section of quad- 

 rate in his figure. On the left side of my figure the otic process 

 of the quadrate extends dorso-posteriorly to unite with the otic 

 capsule. External to this is the anlage of the squamosal. 



It is of interest to note that if a very small portion of the 

 otocyst be left in the mesenchyme, the latter will chondrify in 



