120 DEVELOPMENT OF THE AURICLE IN THE HUMAN EMBRYO. 



as a closure mechanism whose function has remained rudimentary. The presence 

 of the anthelix, the small size and rolled-in character of the helix, and the rudimen- 

 tary character of the auricular muscles are all regarded bjr him as evidences of the 

 reduction of the auricle in man. 



Boas (1912) published the results of a comparative anatomical study of the 

 mammalian adult auricle and its contained cartilage. The work is accompanied 

 by an excellent series of plates illustrating the matter exhaustively. The author 

 has perfected a method of preparing the ear-cartilage so that it can be completely 

 flattened out, thus greatly increasing the possibilities of comparing one form with 

 another. He introduces a new terminology which simplifies the analysis of the 

 different parts of the cartilage. The term plica principalis, used for the cms inferius 

 anthelicis, is a term that will surely be of the greatest value. 



Schwalbe (1916), in a comparative anatomical study of the primate auricle, 

 summarizes and extends his previous studies on this subject. He still regards the 

 auricular hillocks as the basis, in all mammals, for the form of the outer ear. The 

 fact that they are present in reptiles he regards as proof that the organ, which first 

 reaches its characteristic form in mammals, may make its appearance in earlier 

 stages of phylogenetic development. In human embryos the hillocks become 

 modified into a hillock region, whereas there is a fold back of hillocks 4 and 5 from 

 which is formed the free ear-fold or scapha. The variations in this free ear-fold 

 account for the chief differences in ear-tips. The author points out that in those 

 animals that five in water, in subterranean burrows, or in trees the ear-fold is 

 reduced, whereas these forms retain the hillock region, which serves to protect the 

 entrance to the external auditory meatus. The free ear-fold is greatly increased 

 in nocturnal animals. It is of interest to note that similar types of ears may occur 

 in diverse forms living under similar conditions. 



Sera (1917) maintains that the human auricle, with the folded helix and without 

 the Darwin tubercle, constitutes the original and primary form. The unfolded 

 ear with the Darwin tubercle represents an arrest of development and has no 

 phylogenetic significance. 



TERMINOLOGY 



The terminology of the external ear now in general use is a purely descriptive 

 one and is based upon the form usually met with in the human adult. In its estab- 

 lishment scant attention has been given to the embryonic stages and as little to 

 the ear of other animals. It is therefore not surprising than one finds the termin- 

 ology more or less inadequate for any critical analysis of the auricle or for the study 

 of any other ear than that of adult man. When the appropriate time comes, the 

 nomenclature of the external ear will benefit, as much as that of any other part of 

 the body, by a thorough reconsideration. In this paper I shall depart but little 

 from the prevalent terminology and then only where it seems unavoidable. As can 

 be seen in figure 2, the following new terms have been utilized: fossa articular is 

 superior, for fossa triangularis; fossa articular is inferior, for cymba concha?; plica 

 principalis (introduced by Boas, 1912), for crus inferius anthelicis; crus helicis, to 



