120 



THE EAR. 



the organ of Corti like a wire net. The hairlets of the inner hair-cells are 1 J times 

 as long as those on the outer hair- cells (Retzius). On either side of the two sets 

 of hair-cells, the epithelium, becoming gradually shorter, passes continuously into 

 the simple layer of cubical cells which is found in the spiral groove and on the 

 lateral part of the basilar membrane. 



The whole organ is further covered by a thick, fibrillated membrane the factorial 

 membrane (fig. 131, Mt) which is attached at one edge to the upper surface of the 

 limbus, falls over the crest, and rests on the rods of Corti and the hair-cells, thus 

 converting the spiral groove into a canal. It will be necessary to describe more 

 minutely these several parts of the organ of Corti. 



Bods of Corti. The inner and outer ] rods of Corti differ from one another in 

 shape, although agreeing, for the most part, as regards the details of their structure. 



Fig. 137. A PAIR OF RODS OF CORTI, FROM THE 



RABBIT'S COCHLEA, SIDE VIEW. (E.A.S.) 

 Highly magnified. 



6 b, basilar membrane ; i.r, inner rod ; e.r, 

 outer rod. The nucleated protoplasmic masses 

 at the feet are also shown. 



Each inner rod may be best compared in shape to a human ulna, the upper end of 

 the rod being pretty accurately represented by the upper extremity of that bone, the 



Fig. 138. TEASED PREPARATION SHOWING AN INNER AND AN OUTER ROD IN CONNECTION WITH THREE 



HAIR-CELLS, AND PART OF THE LAMINA RETICULARIS (FROM THE GUINEA-PIG). (E.A.S.) Very 



highly magnified. 



i.r, inner rod ; e.r, outer rod ; h v A 2f 7< 3 , hair-cells of first, second, and third rows respectively. 

 They appear, especially the second and third, narrow in the middle, the thin edge of the riband-shaped 

 cell being here seen, but below have become accidentally twisted so that the flattened side is brought 

 into view. A nucleus is visible in h } , but none is seen in h z , A 3 , probably owing to its being contained 

 in the part of the cell the edge of which is turned towards the observer. The lower ends of all three 

 have become broken in the preparation of the specimen ; s, one of the succeeding epithelial cells 

 (cell of Hensen) ; c, cuticular thread attached to lamina reticularis, belonging to a cell of Deiters \ 

 p, phalangeal process of outer rod ; jp 2 , jp 3 , phalanges of lamina reticularis seen in section. 



shape of the olecranon and coronoid processes, as well as the concave articular surface 

 between, being readily recognisable. The upper end of each of the outer rods, on the 



