MIDDLE-EAR REGION OF CALLUS 



241 



slender spicule of bone which is directed laterally and somewhat 

 downward to terminate in the extracolumella. It is flattened 

 from before backward as it approaches its lateral extremity. 

 The columella occupies a recess formed by a diverticulum of the 



Fig. 4 Dissection of the middle ear of an adult chicken, somewhat schema- 

 tized. 1, columella; 2, columellar foot-plate; 3, infrastapedial; 4, suprastapedial; 

 5, extrastapedial ; 6, middle drum-tubal ligament; 7, drum-marginal air sinus; 

 8, columellar-squamosal ligament; 9, ligamentum annulare; 10, membrana tym- 

 pani secundaria; 11, M. tensor tympani. 



tympanic cavity under the carotid canal, ossifies early, and, in 

 the young bird, is relative plump and better developed than 

 the extracolumella (fig. 3). 



The description of the extracolumella is more difficult because 

 it consists of a cartilage tripod with the three processes set at 

 right angles to each other. Figure 4, drawn from the actual 

 dissection, gives the general form of the structure fairly well in 



