THE SENSE ORGANS 153 



over of the edgfe of the ear, and in the greater development of 

 the antihelix. The tip, at the same time, shifts down along the 

 posterior edge of the helix, without, however, becoming rolled in ; 

 and there thus arises the so-called Cercopithecus form (cf. Fig. 71, 

 D) of the human embryo. 



If the rolling in of the tip takes place, we have a third type 

 of ear, in which the tip is turned forwards (Darwin's tipped 

 ear). This (Fig. 71, E) is the usual condition of the human 

 adult, but many modifications of it are realised, the tip some- 

 times entirely disappearing as a free projection. 1 



Besides the degeneration which finds its expression in the 

 reduction of the human ear-fold or pinna, 2 its cartilage is also 

 degenerating. The external auditory passage is among the lower 

 Mammalia (Marsupials) beset by three separate cartilages, movable 

 upon each other. The auditory canal of the child still distinctly 

 reveals this structure, although the alleged complete independence 

 of the basal piece affirmed by Burkner has not been fully estab- 

 lished (Schwalbe). The original clefts between the cartilages are 

 incompletely retained as the incisurse Santorini. 



Secondly, the cartilaginous spina helicis (processus spinosus 

 helicis) is completely fused with the other cartilages of the pinna. 

 It corresponds in position with the free tip of the organ, and is 

 the homologue of a cartilage which, in many Mammals (Ungulata, 

 Carnivora, Eodentia), is independent, and is known as the scutulum 

 (clypeus or rotula). This scutulum fuses with the principal cartilage 

 of the ear in the Lemuroidea and the Apes, as well as in Man. 3 



1 One curious variation is the occurrence on only one side of Darwin's process. 

 In a batch of military recruits it was found to be of medium size on the right side in 

 330 men, and on the left only in seventy-nine, and was thus four times as frequent on 

 the former as on the latter. It was found to be remarkably large on the right side 

 in ten individuals, and on the left only in one (Ammon). 



2 The ear-fold may undergo reduction in Mammals which live underground or 

 in water. The rudiment of a pinna has been found in the embryos of some Whales 

 [and a structure which has been similarly interpreted may occasionally appear in the 

 adult Cetacean]. According to this, the ancestors of existing Whales must have 

 possessed an external ear, and since such an organ would occur in land animals, 

 we find in this fact a proof of the descent of the Whales from terrestrial Placentalia 

 (Kiikenthal). 



3 In rare cases the scutulum may remain separate, even in Man. The familiar 

 lobulus auriculie, a non- cartilaginous fatty tegumental fold, first occurs in the 

 Anthropoids. In Man it undergoes many variations of form and size, and is not 

 infrequently entirely absent. It is never found in people of genuine Kyban descent, 

 nor in the Cagots of the Pyrenees (lilanchard). 



I have to thank Herr Otto Ammon of Carlsruhe for the following statistics 

 obtained by him in connection witli the military recruiting in Baden for 1889 : 

 In 4171 ears (of 2086 men) in the military district of Mosbach, the free lobe was 



