DEVELOPMENT OF THE AURICLE IN THE HUMAN EMBRYO. 117 



in ear dimensions, occurring with advancing age, as due to the flattening out of the 

 various folds of the auricle. This he regards as connected with the loss of elasticity 

 of the elastic fibers of the skin and cartilage, and as related to the wrinkling of the 

 skin which accompanies loss of elasticity in the aged. 



In his next paper, Schwalbe (18916) points out the significant fact that in 

 reptiles that lack an external ear (lizard and turtle) there occur distinct hillocks in 

 the embryo, resembling those in vertebrates that develop an auricle. These hillocks 

 undergo degeneration and are reduced to the level of the surrounding skin. He 

 finds in both birds and reptiles hillocks corresponding to the tragus and antitragus 

 hillocks of His. These animals have one hillock ( Auricularkegel) , situated dorsal 

 to the first cleft, which seems to represent a more primitive apparatus than is present 

 in mammals, although it may be related to the helix system. In Salachians it 

 possesses a spiracle. 



Schaeffer (1892-1893), reviewing the embryonic stages of the auricle, endeavors 

 to trace them to their phylogenetic representatives in adult mammals. He de- 

 scribes the six hillocks as found in the embryo and notes their change in form in the 

 18-mm. embryo, which change he regards as due to opacities of the covering skin. 

 The opacities are produced by cell accumulations, which usher in the fibro-cartilage 

 of the auricle. The first part of the auricle to make its appearance is the inferior- 

 posterior part of the helix. This is followed by the tragus and antitragus and 

 finally (20 mm.) by the crus helicis. Schaeffer points out that the anterior crus 

 of the anthelix is present in all mammals. The folds of the anthelix, which can be 

 seen in the 50-mm. embryo, are present only in Primates. The lobule is a later 

 acquisition and is found only in anthropoids and man. 



In 1897 Schwalbe published an account of the development of the auricle in 

 the human embryo which ranks with that of His (1885) in having dominated all 

 subsequent descriptions. He describes the six hillocks substantially in the same 

 manner as was done by His. The auricle, however, he regards as quite separate in 

 origin from the hillocks. It appears as a fold of skin, resembling an eyelid, caudal 

 to hillocks 4 and 5. (This fold of Schwalbe's corresponds fairly closely to the 

 helix hyoidalis of Gradenigo.) From the region corresponding to hillocks 2 and 3 

 is formed the helix ascendens, the lower end of which becomes the crus helicis. 

 Above, the helix ascendens is continuous over the first gill-cleft with the main 

 ear-fold, the point of union being sharply kinked and corresponding to the crown 

 angle (satyr tip) of the mature ear. The helix ascendens does not exactly corre- 

 spond to the helix mandibulars of Gradenigo, in that the tragus is not derived from 

 its lower end. Schwalbe derives the tragus from hillock 1, as did His; the antitragus 

 he derives from hillock 6. Like Gradenigo, he derives the lobule from the lower end 

 of the ear-fold (helix hyoidalis). He traces hillock 4 into the anthelix system, 

 especially into the inferior crus of the anthelix. The crista anthelicis inferior is 

 probably derived from hillock 5. With the further development of the free ear- 

 fold, three important angles can be recognized along its margin: (1) at the junction 

 of the helix ascendens and the ear-fold, the crown angle or satyr point; (2) in the 

 middle of the ear-fold, the posterior angle or Darwin point; and (3) at the lower 



