152 THE STRUCTURE OF MAN 



The pinna of the ear deserves special attention. In recent 

 years it has been thoroughly investigated by Schwalbe, the results 

 of whose researches are here incorporated. This pinna (p., Fig. 90) 

 is so elaborately modelled a structure that we can hardly imagine 

 it to be degenerate. It undergoes marked variation and adapta- 

 tion in different races, tribes, and individuals, as well as at 

 different ages. On close examination, variation is found, for the 

 most part, to affect those portions of it which stand out freely 

 from the head in a postero-dorsal direction. Schwalbe calls these 

 parts the " ear-folds," distinguishing the basal region as the zone 

 of the auditory prominence (cf. Fig. 71). 



The pinna of Man arises from six prominences which develop 

 near the anterior visceral cleft (au., Fig. 90), and are called the 

 branchial auricular prominences. In the adult pinna they are 

 still evident as the helix, crus antihelicis inferius, crus helicis, 

 tragus, and antitragus (cf. Fig. 71). The human pinna, as 

 compared with that of Apes, would appear to be a degenerate 

 structure ; and in reality it is much reduced, being rolled over 

 in such a way as greatly to modify the upper edge of the helix 

 and part of the antihelix. 



The variations of the ear -folds are of great interest, and 

 deserve close attention, in connection with the primitive history 

 of Man. 



When we examine the highly movable ear of the Ungulata, 

 we find that the ear-fold gives rise to a very efficient sensitive 

 auditory funnel, which lies parallel to the axis l of the ear, and 

 ends in a free tip (spina). 



In the Primates the pinna is much shortened, and is thrown 

 into folds (helix and antihelix) running at right angles to the 

 axis of the ear. Schwalbe finds two forms of free tip in the 

 Apes. (1) The Macacus or Inuus type (Fig. 71, C) ; and (2) the 

 Cercopithecus type (Fig. 71, D). In the former (C), which some- 

 what resembles in shape the ear-fold in human embryos at from 

 the fourth to the sixth month, there is a freely developed edge of 

 the helix which is not rolled over, and a distinct tip, always in 

 the same place. 



From the eighth month, the human ear-fold enters upon a 

 degenerative process, which essentially consists in the rolling 



1 By the axis of the pinna (regarded as a standard of measurement) is meant 

 a line which connects the true tip of the ear (Woolner's and Darwin's tip [spina]) 

 with the incisura auris anterior (cf. s.',s.",s."', Fig. 71, B). By the breadth of the 

 organ, in both Man and the lower mammals, is understood the measurement of the 

 attached portion (base of the ear). 



