514 STUDIES IN ADVANCED PHYSIOLOGY. 



the three diameters of a cube. One is vertical, the other 

 vertical at right angles to this, and the third horizontal. 



Fig. 158. RIGHT BONY LABYRINTH SEEN FROM THE OUTER SIDE. (After Sbmmerring.) 

 The smaller figure below gives the actual size. 1, vestibule; 2, foramen ovale; 3, 4, 5, 

 semicircular canals; 6, 7, 8, cochlea; 9, foramen rotundum. (The immediate walls of the 

 bony labyrinth are denser than the outer portions, and the view above results when the 

 softer bone has been, piece by piece, picked away.) 



2. Cochlea. At the forward end of the vestibule this 

 space communicates with the cochlea. This structure, 

 named from its resemblance to a snail shell, has two and 

 one-half windings. It is a tube coiled up like a snail shell, 

 possibly merely to save space. Drawn out it would be a 

 straight tube not unlike a small dinner-horn. 



The cavity of this coiled tube is, however, divided into 

 an upper and a lower chamber, the upper one being called 

 the scala vestibuli, the lower the scala tympani. The divi- 

 sion is formed partly by a partition of bone called the lamina 

 spiralis and partly by a thin membrane called the basilar 

 membrane. These two chambers are so arranged that the 

 scala vcstibtili is a direct continuation of the cavity of the 

 vestibule. 



The scala vestibuli runs to the top of the cochlea, and 

 at the top, on account of the absence of the partition at 

 this point, it communicates with the scala tympani, while 

 the scala tympani at its lower end communicates with the 

 middle ear through the round foramen. Both these scalac 

 are filled with perilymph. 



