DEVELOPMENT OF THE AURICLE IN THE HUMAN EMBRYO. 133 



bar (cms helicis and tragus) and the derivatives of the hyoid bar (scapha-helix, 

 anthelix, antitragus, and lobule). In the last specimen on this plate (fig. 50), in 

 contrast with figure 49, there are no distinct transverse folds, but the plica princi- 

 palis is more prominent. 



The photographs shown on plate 6 are taken from specimens in the fifth month 

 of development, with the exception of the last, which has a menstrual age of 23 

 weeks. Figures 51 and 52 represent flattened types of auricles, such as that depicted 

 in figure 46 (plate 5). One might think that this was due to flattening of the ear 

 by handling of the specimen, but such is not the case; the specimens were in good 

 condition and had not been subjected to any mechanical damage. In my opinion 

 they can be interpreted only as early exhibitions of a poorly marked helix so com- 

 monly seen in the adult. Both of these specimens show a tendency toward a 

 double tragus. In one the larger segment is above and in the other below. The 

 specimen shown in figure 53 is similar to the type shown in figure 49 and is charac- 

 terized by a marked development of the transverse ridges across the anthelLx. 



In figure 54 the auricle has a well-defined helix at its upper end, together with a 

 tendency toward a satyr-tip. The lower half of the helix is less well marked. 

 In this respect it represents a type seen in adults and known as the Cercopithecus 

 type, as described by Schwalbe (1891). In this ear, as in all the succeeding ones, 

 the plica principalis can be clearly recognized. Figure 55 shows a very perfect 

 type of auricle, the one most usually seen, and for the first time we meet with a 

 well-defined concha, its upper half subdivided by the plica principalis into a superior 

 and an inferior articular fossa. 



The specimen in figure 56 is interesting, in that it still shows the remnants of 

 transverse folds over the anthelix. The fact that there is a tendency toward 

 similar folds along the margin of the helix is strongly indicative of then being 

 nothing more than a temporary expression of the condition of the soft tissues. 

 The auricular cartilage never takes any part in their formation. The specimens 

 shown in figures 57 and 58 both have a well-marked helix. In figure 58 the scapha 

 is somewhat larger and there is a distinct tuberculum. 



Figure 59, which closes the series, shows an auricle having all the essential 

 characteristics of the mature ear. In comparing figure 59 with the first figure on 

 this plate it will be seen that in the course of a month the auricle has about 

 doubled in size. This was true also in the two preceding plates. The auricle in 

 figure 59 is of a simple type, having a marked helix only along its upper border. 

 There is now a distinct concha the definite parts of which can be clearly identified. 

 The hair follicles are well developed over the whole of its surface. In comparing 

 this with the auricles shown on plate 4, the marked difference in the relative sizes 

 of the mandibular and hyoid derivatives is very evident. 



SUMMARY. 

 In describing the development of the auricle, most investigators have traced 

 its origin to the six branchial hillocks, which make their appearance at the fifth 

 week as rounded nodules on the mandibular and hyoid bars adjacent to the first 



