DEVELOPMENT OF THE AURICLE IN THE HUMAN EMBRYO. 131 



should keep in mind the considerable variation which occurs in the form of the 

 ear in adults, for this appears to be expressed in the earliest developmental stages. 

 The photographs, however, are sufficiently numerous to make it possible to separate 

 the constant characteristics from the incidental variations due to normal differences 

 in the auricle and differences in the preservation of the specimens. 



The photographs on plate 4 are specimens from the third month of intrauterine 

 life. The first two (figs. 28 and 29) overlap the oldest stage shown on plate 3; 

 most of the parts of the auricle can here be clearly recognized, although they are 

 still very simple in form. Derived from the mandibular bar are the tragus and the 

 cms helicis; as derived from the hyoid bar, one can recognize the antitragus and 

 the ridge-like primitive ear-fold or scapha-helix. The incisura intertragica, at the 

 entrance of the concha, still bears a resemblance to the hyoid cleft from which it 

 was derived. The concha does not acquire its concave, shell-like character until 

 later in development, due to the relatively thick and swollen character of the sur- 

 rounding parts. Figures 30 to 32 differ from the preceding ones only in the in- 

 creasing prominence of the ear-fold. At this time there is very little surface evidence 

 of the anthelix as distinct from the scapha-helix. However, if sections through 

 this region are examined microscopically, it will be found that the cartilaginous 

 auricle is already characteristically folded into a helix, scapha, anthelix, and concha, 

 the free edge of the helix coming into close contact with the surface of the 

 auricle. 



Figure 33 was taken from a slightly different angle and thus exaggerates the 

 taenia lobularis. In the earlier stages the taenia stands out more prominently. 

 The lobule forms a free fold between the taenia and the lower end of the helix, 

 principally at the expense or as an elaboration of the taenia. The latter thus be- 

 comes relatively less conspicuous. 



In figures 34 and 35 the anthelix makes its appearance on the surface of the 

 auricle for the first time, and as it does so a groove develops between it and the 

 free edge of the auricle, representing the early scapha. A lobule can also be recog- 

 nized as a rounded expansion from the taenia. The small tubercle on the posterior 

 edge of the helix in figure 35 is due to a thickening of the skin and is to be regarded 

 only as a peculiarity of this particular specimen. Figures 36 to 38 show a distinct 

 increase in the size of the auricle. In these there is some differentiation of the 

 scaphal groove and a corresponding prominence of the helix. The specimen shown 

 in figure 39 is from a fetus larger than any of the preceding specimens. It falls in 

 this place because the photographs are arranged in the order of fetal length; the 

 auricle, however, shows a somewhat retarded degree of differentiation and in form 

 resembles the specimen illustrated in figure 35. In size it corresponds fairly 

 closely to its neighbors, and we may perhaps assume that if the fetus had gone on 

 to term it would have had a simplified type of auricle and possibly a prominent 

 taenia lobularis or an attached lobule. The method of illumination in making the 

 photograph shown in figure 40 exaggerates the prominence of the antitragus. I 

 am introducing it on this account, in order to illustrate the marked differences in 

 appearance one can secure by a modification of the illumination. The auricle 



