88 THE SCAFFOLDING LEFT IN THE BODY. 



mainly effected by a -series of remarkable develop- 

 ments of one of the now superfluous gill-slits. 



It has long been a growing certainty to Comparative 

 Anatomy that the external and middle ear in Man are 

 simply a development, an improved edition, of the 

 first gill-cleft and its surrounding parts. The tym- 

 pano-Eustachian passage is the homologue or counter- 

 part of the spiracle associated in the shark with the 

 first gill-opening. Prof. His of Leipsic has worked 

 out the whole development in minute detail, and con- 

 clusively demonstrated the mode of origin of the 

 external ear from the coalescence of six rounded 

 tubercles surrounding the first branchial cleft at an 

 early period of embryonic life. 1 



1 Haeckel has given an earlier account of the process in the 

 following words : " All the essential parts of the middle ear the 

 tympanic membrane, tympanic cavity, and Eustachian tube 

 develop from the first gill-opening with its surrounding parts, 

 which in the Primitive Fishes (Selachii) remains throughout life 

 as an open blow-hole, situated between the first and second gill- 

 arches. In the embryos of higher Vertebrates it closes in the 

 centre, the point of concrescence forming the tympanic mem- 

 brane. The remaining outer part of the first gill-opening is the 

 rudiment of the outer ear-canal. From the inner part originates 

 the tympanic cavity, and further inward, the Eustachian tube. 

 In connection with these, the three bonelets of the ear develop 

 from the first two gill-arches ; the hammer and anvil from the 

 first, and the stirrup from the upper end of the second gill-arch. 

 Finally, as regards the external ear, the ear-shell (concha auris), 

 and the outer ear canal, leading from the shell to the tympanic 

 membrane these parts develop in the simplest way from the skin 

 covering which borders the outer orifice of the first gill-opening. 

 At this point the ear-shell rises in the form of a circular fold of 

 skin, in which cartilage and muscles afterwards form.' 1 Haeckel, 

 Evolution of Man, Vol. ir., p. 2G9. 



