116 DEVELOPMENT OF THE AURICLE IN THE HUMAN EMBRYO. 



Gradenigo (1888) presents a study of the development of the auricle in a series 

 of mammals, including man, pig, cat, guinea-pig, rabbit, sheep, and cow. In the 

 last three his studies were controlled by serial sections. Like the previous authors, 

 he found six hillocks, three on the mandibular arch and three on the hyoid arch. 

 According to Gradenigo, the hillocks flatten out and tend to fuse together. The 

 four lower ones, by closing in around the lower hyomandibular groove, form the 

 external auditory meatus and the floor of the future fossa angularis. In doing this 

 the hillocks disappear for the most part. The hillocks do not form the auricle 

 proper; this arises through the fusion of two elevations immediately adjacent to 

 the hillocks, which the author names helix hyoidalis and helix mandibularis. These 

 elevations appear at about the time of the flattening out of the hillocks. In later 

 stages these two elevations fuse above and below, thus surrounding the region of 

 the hillocks and thereby forming the auricle. The hillock region corresponds to 

 the fossa angularis and becomes the future concha and the entrance to the external 

 auditory meatus. In tracing the formation of these elevations from which the auricle 

 is derived, Gradenigo points out that the helix hyoidalis first makes its appear- 

 ance just behind the middle hyoid hillock and from there spreads behind the other 

 two hyoid hillocks. Its upper end arches forward over the region of the hillocks. 

 At this stage in its development we have a structure resembling the cauda of the 

 thud hillock of His. The helix mandibularis makes its appearance somewhat later 

 than the helix hyoidalis, its upper part being better developed than the lower part. 

 The lower part forms the tragus. In addition to fusing above and below, the helices 

 develop processes which extend transversely across the fossa angularis. One of 

 these becomes the eventual crus helicis, and another forms part of the crus inferius 

 anthelicis. The other processes become lost. The paper is not very well illus- 

 trated, so that it is difficult to follow the author's description in detail. However, 

 he reviews the pathology of this region and gives an account of a variety of terato- 

 logical conditions. He points out that the lobule makes its appearance later in 

 man than in other mammals and that it is derived from the growth of the lower end 

 of the helix hyoidalis. 



His (1889) gives a morphological description of the adult auricle in man. He 

 goes into particular detail regarding the lower part of the ear, especially the lobule. 



Schwalbe (1889), in the first of a series of important papers on the development 

 of the auricle, briefly describes the form of the auricle in human fetuses ranging 

 from 60 to 180 mm. sitting height, and in doing so he introduces the more accurate 

 technique of physical anthropology. He points out that the crown of the ear 

 (satyr tip) is not the same as the Darwin angle. The Darwin angle is the true ear- 

 tip and first makes its appearance in the human fetus about the middle of the third 

 month. It becomes less distinct in the later months, due to its thickening and the 

 rolling in of its edge. The rolling in of the ear he regards as a reduction process. 



Schwalbe (1891a), in his next paper, discusses the Darwin tubercle (i. e., the 

 true ear-tip) as it occurs in adult man. He describes six degrees of its occurrence, 

 varying from the most pronounced type, resembling the Macacus form, to the least 

 marked, where no trace of the ear-tip can be recognized. He explains the increase 



