OUR FACE FROM FISH TO MAN 



of the air outside the ear-drum. Likewise in all 

 higher vertebrates, including man, the cavity of 

 the middle ear communicates with the throat 

 through the Eustachian tube; this arises in the 



semicircular 

 canals 



f??ecCuUa_^ 

 oblon^oLta 



acoustic 

 nenre 



throat 



mc 

 ring 



tu/npanic 

 membrarip 



stapes 



tumpanic 

 ^caVitif 



Eustachian 

 tube 



Fig. 106. Transverse Section of the Head in a Frog, Showing 



THE Relations of the Middle Ear (there is no Outer Ear) 



to the Inner Ear and of the Latter to the Brain (after 



T. J. Parker and W. N. Parker). 



embryo as an outgrowth of the primitive throat 

 cavity immediately behind the first or jaw arch 

 (Frazer, quoted by Keith). 



The tube of the outer ear of mammals corre- 

 sponds in position partly to the spiracle or hyoid 

 gill cleft of the shark. Both arise also in the 

 embryo as a down-pocketing of the ectoderm, 



which meets an out-pocketing from the throat 



208 



