700 



THE EAR 



e.g., Crustacea, which is simply an equilibrating organ. They are be- 

 lieved to function as static organs of equilibration, giving information 

 as to position at rest or during progressive movements ; the semicircular 

 canals on the other hand are commonly conceived of as dynamic or- 

 gans of equilibration and are thought to furnish information regarding 

 the direction and extent of rotatory movements. 



FIG. 584. TRANSECTION OF A HUMAN SEMICIRCULAR CANAL. 



1, bone; 2, retiform connective tissue membranes; 3, at this point a band of con- 

 nective tissue joins the periosteum; 4> membranous semicircular canal; 5, liga- 

 mentous attachment of the canal; 6, at this point the membranous and osseous 

 canals are in contact. Moderately magnified. (After Riidinger.) 



The cristae are clothed with tall columnar cells which, though some- 

 what taller, are otherwise similar in structure to those of the maculae, 

 and are similarly divisible into sustentacular cells and hair cells. They 

 are also covered by a gelatinous cuticular formation, containing otoliths, 

 which is here known as the cupola. The vibratory stimulus is trans- 

 mitted from the endolymph to the hair cells through the medium of 

 the otolithic membranes. 



