430 THE SENSORIAL FUNCTIONS. 



of the osseous cavity ; being composed of two 

 distinct sacs, opening into each other : one of 

 these (u) is termed the utricle;* and the other 

 (s), the sacculns. Each sac contains in its in- 

 terior a small mass of white calcareous matter, 

 (o, o), resembling powdered chalk, which seems 

 to be suspended in the fluid contained in the 

 sacs by the intermedium of a number of nervous 

 filaments, proceeding from the acoustic nerves (g 

 and n), as seen in Fig. 396. From the universal 

 presence of these cretaceous substances in the 

 labyrinth of all the mammalia, and from their 

 much greater size and hardness in aquatic 

 animals, there can be little doubt that they per- 

 form some office of great importance in the phy- 

 siology of hearing.^ Their size and appearance 

 in the Dog are shown in Fig. 397 ; and in the 

 Hare, in Fig. 398. 



The Cochlea, again, is an exceedingly curious 

 structure, being formed of the spiral convolu- 

 tions of a double tube ; or rather of one tube, 

 separated into two compartments by a partition 

 (l), called the lamina spiralis, which extends its 

 whole length, except at the very apex of the 



* Scarpa and Weber term it the sinus, or alveus utriculosus ; 

 it is called by others the sacculus vestibuli. Breschet gives it 

 the name of le sinus median. See the Memoir already quoted, 

 p. 98. 



t These cretaceous bodies are termed by Breschet otolithes, 

 and otoconies, according as they are of a hard or soft consistence. 

 Ibid. p. 99. 



