THE INTERNAL EAR 



743 



m man, mam- 

 birds and rep- 



of the membrane. A similar spot containing otoliths exists in the saccule 

 at the point of entrance of its nerve. Otoliths are also found in the 

 ampullae of the semicircular canals. These calcareous masses are com- 

 posed of crystals of calcium carbonate, which are hexagonal and pointed 

 at their extremities. Nothing definite is known of the uses of these cal- 

 careous bodies, which 

 exist 

 mals, 

 tiles. 



The membranous 

 semicircular canals oc- 

 cupy about one-third 

 of the cavity of the 

 bony canals. They 

 present small ovoid 

 dilatations, called am- 

 pullae, corresponding 

 to the ampullate en- 

 largements of the 

 bony canals. They 

 are held in place by a 

 large number of little 

 fibrous bands extend- 

 ing to the bony laby- 

 rinth. 



The membranes of 

 the cochlea include 

 the periosteum lin- 

 ing the bony canal, 

 and the true membra- 

 nous cochlea. Viewed 

 externally, the true 

 membranous cochlea 

 appears as a single 

 tube following the 

 turns of the bony cochlea, beginning below by a blind extremity and ter- 

 minating in a blind extremity at the summit of the cochlea. If a section 

 of the cochlea is made in a direction vertical to the spiral, it will be seen 

 that the bony canal is divided, partly by bone and partly by membrane, 

 into an inferior portion, a superior portion, and a triangular canal, lying 

 between the two, which is external. The bony septum is in the form of 

 a spiral plate extending from the central column (the modiolus) into the 



Fig. 191. Diagram of the labyrinth. From a photograph, and 

 slightly reduced (Riidinger) . 



Upper figure : i, utricle ; 2, saccule ; 3, 5, membranous cochlea ; 

 4, canalis reuniens ; 6, semicircular canals. 



Lower figure: i, utricle; 2, saccule ; 3,4,6, ampullae; 5,7,8,9, 

 semicircular canals; 10, auditory nerve (partly diagrammatic); 

 ii, 12, 13, 14, 15, distribution ot the branches of the nerve to the 

 vestibule and the semicircular canals. 



