THE SENSE OK II KAIllNd 



209 



purl of its plate towards the tympanic cavity, and thus diminish- 

 ing the pressure in the labyrinth. Simultaneously, owing to the 

 contraction of the stapedius, the obtuse angle between the incus 

 and the stapes becomes somewhat extended the chain of the 

 auditory ossicles is pushed outwards and the tympanic membrane 

 slightly relaxed, so that the whole of the tympanum becomes 

 capable of more ample vibrations, and the slightest sounds can 

 be perceived. Objections have, however, been raised to Ostmanu's 

 theory. The contraction of the stapedius would have to be 

 continuous or tetanic in listening to a prolonged, gentle murmur, 

 which would produce a weakening of hen ring owing to limitation 



Ht 5 .YI . 



1 



( SMM^ Is 



Fn.. si. Section across cartilaginous part of Eust;ichi;in lulu-. (Rn<liii,'or.) 1, 2, curved car- 

 tilaginous plate; 3, muse, dilator tubae ; to left of 4, part of attachment of levator palati 

 muscle ; 5, tissue uniting tube to base of skull ; 6, 7, mucous glands ; 8, 10, fat ; 9, 11, lumen 

 of tube ; 12, connective tissue at the side of the tube. 



of the movements of the stapes, even apart from the disturbing 

 muscular bruit. 



Politzer particularly insisted on the functional antagonism 

 between the tensor and the stapedius, but gave no experimental 

 demonstration of it. 



V. The Eustachian tube is a canal about 35 mm. long and 

 3.5 mm. wide, which connects the tympanic cavity with the upper 

 end of the pharynx. The first portion of the canal is hollowed 

 out of the petrous bone ; the second portion consists of a curved 

 plate of cartilage, covered by fibrous tissue and mucous membrane. 

 In sections through the cartiliiuinmis part of the tube (Fig. 81) 

 the cartilage is seen in the. form of a hook, the lumen as a slit 

 surrounded by mucous membrane with ciliated epithelium, and 



VOL. IV P 



