118 DEVELOPMENT OF THE AURICLE IN THE HUMAN EMBRYO. 



end of the ear-fold, where it merges into the lobule, the posterior-inferior angle. 

 Schwalbe points out that one can draw a straight line separating the hillock region 

 from that of the free ear-fold. This line falls above the upper end of the helix 

 ascendens and passes down, posterior to the antitragus, to the point of junction 

 of the lobule and the free ear-fold. The hillock region lies in front of this line and 

 is more or less constant in all types of auricles; the free ear-fold lies posterior to 

 the line, and the degree of development of this part of the ear is the chief factor 

 in producing the different types of ears found in various mammals The author 

 describes the occurrence, during the fourth month, of ridges in the free ear-fold, 

 which he regards as the temporary presence of the longitudinal folds that become 

 permanent in some of the other mammals. His paper is accompanied by an in- 

 structive table in which are listed the separate hillocks, their embryological desig- 

 nations, and the part each takes in the formation of the definitive auricle, including 

 the terminology of His and Gradenigo. 



Munch (1897) describes the morphology of the auricular cartilage in human 

 embryos 20, 48, 57, 96, and 142 mm. long, as seen in wax-plate reconstructions. 

 In studying its histogenesis, the author notes the close relationship existing between 

 the cartilage and the ectoderm and describes the characteristic appearance of the 

 ectoderm over the auricular region. He alludes to the relatively large size of the 

 spina helicis in early stages and its subsequent tendency to become pinched off. 

 It seems never to become completely detached in man, but does so in other animals. 

 It is then designated scutulum. 



Ruge (1898) presents a comparative anatomical study (Ornithorhynchus and 

 Echidna) of the cartilage of the auricle. He bases his argument on its adult 

 connections, regarding the cartilage of the auricle as a derivative of the hyoid arch. 

 The tympanic end of the cartilage of the external auditory meatus is most closely 

 connected with the hyoid by connective tissue and common musculature. In 

 tracing it peripherally, its medial terminal part becomes the concha, and the 

 lateral terminal part becomes the tragus. The author emphasizes the unity of 

 the external auditory meatus and the auricle. 



Hammar (1902), in describing the development of the middle ear and external 

 auditory meatus in man, points out that the fossa conchae (angularis) certainly 

 arises directly from the first branchial cleft, and thus we have as derivatives of the 

 first cleft the incisura intertragicus, cavitas conchae, and cymba conchae. All the 

 other furrows of the auricle are secondary. In referring to the hillocks, the author 

 states that he does not find that they take part in the formation of the floor, but 

 rather that the auricle is derived from two ridges that are independent of the 

 auricular hillocks, somewhat as described by Gradenigo (helix mandibularis and 

 helix hyoidalis). The hillocks are not so sharply marked as has been indicated by 

 previous writers. They consist only of slight thickenings of a more or less uniform 

 subepidermal connective-tissue layer. Hammar regards it as artificial to describe 

 them as independent structures which shove over and fuse with one another. 

 He makes the important observation that the hillocks are more or less absorbed 

 in the swellings from which the auricle is derived. 



