RECORDS VOLUME XI, JAN^., 1919. 11 



At a point where the tympaniforms nar- 

 row, a membraneous muscle beo^ins stretch- 

 ing across from tube to tube and adhering 

 to them along the the lower margin of the 

 narrow tympaniforms, fig. 11, A, o, v, v. It 

 is thin, but is strengthened by two ridges of 

 thicker fiber, ib, v, v. The function of this 

 muscle is to draw downward the upper por- 

 tion of the tubes and thus tensing the wider 

 parts of the tympaniforms. This membrane- 

 ous muscle is the bronchidesmus, and bears 

 about the same relationship to the vibrat- 

 ing membrane that the bridge bears the to 

 the strings of a violin. 



The anterior portions of the tympans are 

 attached to the pessulus, a thin bone that 

 crosses the trachea at its junction with the 

 bronchials at the acute angle above o, fig. 1 

 where a diagrammatic section is given, and 

 the unshaded portion, fig. 11, between p and 

 i. The pessulus bears a very slight semiluna 

 membrane, ib. i, so slight, in fact, as to be 

 nearly or wholly functionless. 



