. Journal of morphology . ose tendon fits into and fillsa depression upon its external surface (PL IV, Fig. 35). 558 B. F. Kingsbury and H. D. Reed. The operculum is formed out of the wall of the ear capsule uponthe medial side of the caudal portion of the fenestra. Fig. 23shows the operculum in process of formation. Along the line mark-ing the medial border of the new fenestra the cartilage breaks downand is absorbed, cutting out in this way a large plate from the ventralwall near the caudal end of the ear capsule. In this histolysis, whilethe end result is a backward and medial extension of
. Journal of morphology . ose tendon fits into and fillsa depression upon its external surface (PL IV, Fig. 35). 558 B. F. Kingsbury and H. D. Reed. The operculum is formed out of the wall of the ear capsule uponthe medial side of the caudal portion of the fenestra. Fig. 23shows the operculum in process of formation. Along the line mark-ing the medial border of the new fenestra the cartilage breaks downand is absorbed, cutting out in this way a large plate from the ventralwall near the caudal end of the ear capsule. In this histolysis, whilethe end result is a backward and medial extension of the fenestralopening, it is not accomplished by an actual extension back of thefenestra, but the cartilage is absorbed all along the line of separation,several irregular clefts appearing first which afterwards become con-fluent with each other and with the fenestra. At its caudal end theseparation of the operculum comes later and at this point a newformation of cartilage occurs extending the operculum in that direc-St., Fig. 1. Schema illustrating the fusion of the columella with the earcapsule. tion outside the ear capsule. New cartilage is, however, formed atthe edge of the fenestra as well and in the operculum itself whichattains massive dimensions in the fully grown Ambystoma (PI. IV,Fig. 35). The inclusion of the cephalic end of the operculum by the lipsof the fenestra (PL I, Fig. 24) is accomplished by a deposit ofnew cartilage which cements in solidly the fenestral plate andextends the fenestral lip backward outside the operculum. ThedorsQ-cephalic portion of the margin is thus formed by the ventraland caudal edges of the larval columella extended by new cartilageformation, while the ventro-cephalic margin is new cartilage formedupon the ventral lip of the primary fenestra which extends to deposited on the fenestral plate. The diagram. Fig. 1, will The Columella Auris in Amphibia. 559 illustrate the transformation and the filling in of the primaryfenestra a
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