242 A. G. POHLMAN 



an adult bird. The three processes have received many names 

 of which, perhaps, infrastapedial, suprastapedial, and extra- 

 stapedial are as good as any. We may refer to the common 

 origin of these processes as the common cartilage stalk of the 

 extracolmiiella. The infrastapedial (3) leaves the common 

 cartilage stalk at its union with the columella and extends down- 

 ward, at a right angle to the position of the columella, to termi- 

 nate in a somewhat sharpened extremity close to the drum 

 margin. The attachment of the columella to the extracolumella 

 is somewhat flattened in the axis of the infrastapedial, and 

 results in a movable member in this axis, which may be termed 

 'the columellar hinge.' The suprastapedial (4) is a spatulate 

 process with its pointed extremity downward and forward, where 

 it attaches to the common cartilage stalk, and its widened area 

 correspondingly upward and backward where it attains the 

 postero-superior drum margin. The flattened surface is at right 

 angles to the columellar axis and the plane of its position is 

 about the same as that of the infrastapedial. This process is 

 not only the largest and most firmly attached portion of the 

 extracolumella, but its base, attached to the drum margin, con- 

 stitutes another hinge member which may be called the 'supra- 

 stapedial hinge.' The movement of this hinge is necessarily 

 accompanied by drum displacement, and, in a general way, is 

 outward-downward and inward-upward. The extrastapedial 

 process (5) arises from the cartilage stalk, nearly in the axis of the 

 bony columella, and lateral to the confluence of the infra- and 

 suprastapedials. This process acts like the center pole of a 

 tent and gives the drum membrane its curious inverted umbo to 

 which attention has already been called. The extrastapedial 

 receives most of the fibers of the M. tensor tympani, the drum 

 course of w^hich can readily be identified by inspection; some- 

 times the extrastapedial cartilage is particularly well developed 

 out along the drum in the direction of the tendinous fibers. This 

 process varies markedly in different ages and in different species 

 of birds. Its greatest movement occurs at the union of the 

 three cartilage processes and is a hinge, practically in the plane 

 of the action of the M. tensor tympani. These hinge areas in 



