INTERNAL EAR OR LABYRINTH. 



375 



The membranous semicircular canals, as lias been stated, 

 are much smaller than the osseous tubes in which they are 

 situated, have the the same form, and present the same 

 number of ampullae. They are likewise distended with the 

 fluid of Scarpa, and separated from the osseous semicircular 

 walls, by the fluid of Cotunnius. 



In the sacculus communis, and proprius of the vestibule, 

 Breschet discovered two white, shining masses, composed 

 of phosphate and carbonate of lime, held together by ani- 

 mal matter. Being in the form of powder, or dust, he 

 called them otoconia, (01^, the ear, and songs dust.) This 

 ear-dust, or calcareous matter, floats in the fluid of Scarpa. 



Nerves of the Ear. The nerves of the ear come from the 

 seventh, the fifth, the eighth pair the cervical plexus, 

 and the sympathetic. The portio mollis of the seventh 

 pair is the especial nerve of hearing, entering the in- 

 ternal auditory me- FIG. 109. 

 atus. It divides, at 

 the cribriform base 

 of this meatus, into 

 two branches the 

 anterior and larger, 

 going to supply the 

 cochlea, and the pos- 

 terior and smaller, 

 passing to the vesti- 

 bule and semicircu- 

 lar canals. 



The anterior, or 

 coclilear branch, has 

 a spiral direction, and has been compared to a flat tape, 

 rolled on itself. At the base of the meatus internus it 

 enters the foramina, in the tractus spiralis, by numerous 

 minute filaments which spread out upon the surface of the 



FIG. 109 represents the Labyrinth, laid open and inverted, so as to show 

 the distribution of its nerves, a 6 c Cochlea laid open, d ef Remains of the 

 parietes of the cochlea, g h Vestibule, i i Superior semicircular canal, kl 

 Inferior or horizontal canal, m Posterior canal, n n Semicircular mem- 

 branous canals, op q Auditory nerves passing to the labyrinth. 



