OUR FACE FROM FISH TO MAN 



descending helix and lobule. According to Keith 

 (1921) in the human embryo of the sixth week all 

 but the marginal fold arise from six tubercles that 

 form around the first gill cleft depression. 



Three of these tubercles [writes Keith] grow from the 

 mandibular or first arch and form the tragus, crus of the 

 helix, and helix; three from the hyoid arch to form the 

 lobule, antitragus and antihelix. The hinder margin of the 

 ear, or descending helix, with the lobule, arise as a mere 

 thickening or elevation of the skin behind the tubercles in 

 the hyoid arch. Later in development the tubercles of 

 the helix and antihelix send out processes which cross the 

 upper part of the cleft and obliterate it, while the neigh- 

 boring tubercles fuse to form the definite parts of the ear. 

 The posterior margin and lobule rise up at the same time 

 as a free fold. 



Fig. 109. Ears of Fcetal Macaque (A) and of a Six Months 

 Human Fcetus (B). (From Plate, after Schwalbe.) 



(From Allgem. Zool., Gustav Fischer.) 



The common lemur {Lemur catta) of Madagascar 

 has very large pointed ears that can be directed 

 forward. In the monkeys the ear tends to 

 be flat with a rounded top, quite different 

 from the trumpet-like ear and not capable of 



being thrust far forward. The ear of the Old 



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