762 SPECIAL SENSES. 



arrangement of the pillars, or rods of Corti. They are nearly homogeneous, 

 except when treated with reagents, and are said to be of about the consistence 

 of cartilage. They are closely set together, with very narrow spaces between 

 them, and it is difficult to see how they can be stretched to any considerable 

 degree of tension. The arch is longer at the summit than at the base of the 

 cochlea, the longest rods, at the summit, measuring, according to Pritchard, 

 about ^-g- of an inch (125 /*), and the shortest, at the base, about -gfa of an 

 inch (50 /t). At the base of the cochlea the two sets of rods are about equal 

 in length. From the base to the apex, both sets, outer and inner, progress- 

 ively increase in length, and the outer rods become the longer, so that near 

 the apex they are nearly twice as long as the inner. The anatomical rela- 

 tions between the pillars and the terminal filaments of the auditory nerves 

 are not definitely settled. 



In addition to the pillars just described, various cellular elements enter 

 into the structure of the organ of Corti. The most important of these are 

 the inner and the outer hair-cells. These are 16,400 to 20,000 in number 

 (Hensen, Waldeyer). The inner hair-cells are arranged in a single row, and 

 the outer hair-cells, in three rows. Nothing definite is known of the uses of 

 these cells. The relations of these parts are shown in Fig. 274. It is sup- 

 posed by some anatomists that the filaments of the auditory nerves terminate 

 in the cells above described ; but this point is not definitely settled. 



USES OF DIFFERENT PARTS OF THE INTERNAL EAR. 



The precise uses of the different parts found in the internal ear are ob- 

 scure, notwithstanding the careful researches that have been made into the 

 anatomy and the physiology of the labyrinth. There are several points, 

 however, bearing upon the physiology of this portion of the auditory appa- 

 ratus, concerning which there can be no doubt : 



First, it is certain that impressions of sound are received by the terminal 

 filaments of the auditory nerves and by these nerves are conveyed to the 

 brain. 



Second, the uses of the parts composing the external and the middle ear 

 are chiefly accessory. The sonorous waves are collected by the pavilion and 

 are conveyed by the external meatus, to the middle ear ; the membrana tym- 

 pani vibrates under their influence ; arid they are thus collected, repeated and 

 transmitted to the internal ear. 



Uses of the Semicircular Canals. In the experiments of Flourens, upon 

 pigeons and rabbits (1824), it was shown that destruction of the semicircular 

 canals had apparently no effect upon the sense of hearing, while destruction 

 of the cochlea upon both sides produced complete deafness. In addition it 

 was observed that destruction of the semicircular canals on both sides was 

 followed by remarkable disturbances in equilibration. The animals could 

 maintain the standing position, but so soon as they made any movements, 

 " the head began to be agitated ; and this agitation increasing with the move- 

 ments of the body, walking and all regular movements finally became impos- 

 sible, in nearly the same way as when equilibrium and stability of move- 



