PROPORTIONS OF THE TECTORIAL MEMBRANE 



51 



increase in width is mostly attained in that part of the lip upon 

 which the axial zone of the tectorial membrane is attached, that 

 is, from the insertion of the vestibular (Reissner's) membrane 

 to the edge of Huschke's teeth, and the edge of Buschke's teeth 

 projects outward farther in the full term fetus and adult than in 

 the earlier stages (compare figures 2 to 7) . The average widths of 

 this part of the hp, which is most of it, are given in table 5. 

 The greater variations in the averages for the width at the 1st 

 half turn are due to the varying distances from the tip end of 

 the lip at which the knife passed, for the lip narrows suddenly 

 in terminating in the hammulus. The slight increase in width, 



TABLE 5 



Givmg in micra averages uf the width of the vestibular lip of the spiral iimbus from 

 the insertion of the vestibular membrane to the edge of Huschke's teeth in the dif- 

 ferent sizes of the pig and the different turns of the cochlea specified 



shown in the table, between 13 cm. and 22 cm. can have little 

 to do with other than the growth of the attached axial zone of 

 the membrane. At 13 and 14 cm. the part of the lip in the 1st 

 half turn is not sufficiently outlined to measure. Most of the 

 increase seems to occur after 22 cm., that is, between this and 

 the fetus at term and the adult, when the membrane is becoming 

 and has become detached from its parent cells and from the 

 spiral organ. This latter increase in the width of the Up may 

 contribute a sUght projection of the tectorial membrane out- 

 ward and over the spiral organ. The width of this part of the 

 lip is about the same as the width of the attached axial zone of 

 the membrane. 



