GROWTH OF THE INNER EAR OF ALBINO RAT 77 



11. The greatest height of the tunnel of Corti. Some authors 

 have reported in several animals the appearance of the tunnel 

 of Corti just after birth, or even in later intrauterine life. In 

 the rat, however, it first appears through all the turns after 

 the ninth day. Sometimes we see it at nine days in the lower 

 turn, though not yet in the upper. The method of measuring 

 the height is shown in figure 1, line 1-1'. Table 49 (charts 21 

 and 22) gives the values for the greatest height of the tunnel of 

 Corti. At the foot of the last column are given the ratios from 

 12 to 25, 12 to 546, and 25 to 546 days. 



As the table shows, the space appears in all the turns at twelve 

 days and has considerable height. This increases to twenty-five 

 days, than decreases very slowly. This increase and decrease 

 correspond to the changes in the distance of the summit of the 

 pillar cells from the basilar membrane. 



When we consider the height in each coil of the cochlea, we 

 find the value increases from the base to the apex, first rapidly 

 then slowly. In table 50 this relation is clearly shown. 



Retzius ('84) gives the values for the adult rabbit, man and 

 cat (one month) as follows (table 51). 



According to this table, the average height is in the adult 

 man, cat, and rabbit somewhat less than in the rat. 



12. The height of the papilla spiralis at the third series of 

 the outer hair cells. The measurements were taken along the 

 line 2-2 shown in figure 1. The growth of this vertical height 

 depends not only upon the increase of the length of the corre- 

 sponding outer hair cell, but chiefly upon the development of 

 the Deiters' cells, especially of the outermost row, and of the 

 sustentacular cells of Hensen. 



In table 52 (charts 23 and 24) are given the values for this 

 vertical height of the papilla spiralis at the third series of the 

 outer hair cells according to age. At the bottom of the last 

 column are the ratios at 1 to 12, 1 to 20, 1 to 546, and 20 to 546 

 days. The heights decrease at three days, but increase from 

 nine to twelve days very rapidly, nearly doubling their minimal 

 values, and reach a maximum at twenty days. After that time 

 they decrease very gradually to the end of the record. There- 



