mi: OBOAHI Off MM. < 511 



7. The tympanic membrane. \\lii.-h at 



only gradually becomes reduced to tonne membrane, i 



velopfd out of tin- do and the 



adjacent jiai ts of the vi-ceral ai. 



I'll.- tympanic ca\itv and tin- KM ,.-ln;iM tube are developed 

 >ut >f a depres>ion on the median >ide .,f tin- tympanic membrane, 

 the >ulcu- t tibo tympanicus, -and ..nt OJ 

 extending ui> \ard. an I pd. 



9. The tympanic ca\itv is ai i inely small, the conn* 



tis>u of tin* inucoiiv ini'iiilr.in th.-i- nig gelatinous 



[ami voluminous]. 



1<. Tin- amlii-.i-y otBudefl au-l tin- ohordi tympani lie at first 



ut>iilr tlio tympanii- caxity in ti.t- p-latinoii> 



only aft.-i- .^lirivcllin^ of I In- p-latinous tin- that ,:ae to He 



in folds of tin 1 niuo.ni- m niliraiie. which project into tlu- now more 

 capacious tympanic cavity (inru>-f>M. mall'ii>-fol<l). 



11. Tlu- cxit-rnal mratu> is .Icvclopi'.l from th- v of the 



depression that lies on the lateral >I<1- of th- tympanic membrane; 

 the auricle arises from six elevation-, which an- converted 

 is. antitragus, helix, antihclix. and tin- lolmlr of the ear. 



C. The Development of the Organ of /, 



The (r:raii of smell is, like tin- eve aiid ear, a product of t ; 

 <: TIII -layer, from which it is developed somewhat later than the two 

 higher sensory organs. It first becomes noticeable, at either side 

 of the broad frontal pmce-> (ti.ir. -7 h previously dex-ribed, as a 

 thickening of the outer ^--rm-layer which His has designated in 

 human < mhry, /. Hot h fundaments soon become more 



distinct owini: to the fact that ea.-h nasal area becomes depressed 

 into a kind of trough, the edges of which ri>e up as folds < : 

 An olfactory lobe, which has been formed m-antime by an evic- 

 tion of the cerebral vesicle, grows out on either >ido to tin- thick- 

 ened epithelium of thi> area, where n :trill:e terminate. 



The tu" ich :ire ; :. :i >imilar manner in 



all Vertei rh the -\ lostomes, in which 



an unj aired pit arises, are separated from eac by a con- 



able di>tanc.-. They ther ly paired 



structures, whereas in their ultimate condition in the h; 

 Vertebrate they have approached . ach other toward the nc 

 plane and become an apparently unpaired organ, the nose. 



