132 DEVELOPMENT OF THE AURICLE IN THE HUMAN EMBRYO. 



shown in figure 41 is from a fetus from the end of the twelfth week, and aside 

 from a poorly defined concha it represents most of the elements of the mature 

 auricle. 



On looking back over the auricles illustrated on this plate, one can see that in 

 all of them the mandibular derivatives the crus and tragus are relatively large 

 and prominent as compared with the hyoid derivatives. In the further develop- 

 ment of the auricle this proportion gradually decreases. It will be further noted 

 that the crus helicis is always a distinctly separate structure from the helix proper; 

 the line of demarcation between them persists in the adult. 



The photographs shown on plate 5 represent the changes occurring in the 

 auricle during the fourth month of intrauterine life. As compared with the photo- 

 graphs on plate 4, the principal change is a relative decrease in the size of the crus 

 helicis and tragus. Corresponding to this, it is possible to recognize a conchal 

 cavity which has heretofore been nothing more than a cleft. The concha in the 

 first two photographs (figures 42 and 43) appears to me a little exaggerated, due, 

 probably, to the shrinkage of the auricle. Judging from the preceding and suc- 

 ceeding photographs, the average auricle at this time would be somewhat plumper 

 in appearance. Owing to the fact that these are thinner, one can see for the first 

 time the presence of the plica principalis. 



The specimen shown in figure 44 exhibits the average fulness in the region of 

 the anthelix, with a tendency to be thrown into transverse ridges. These ridges 

 occur in this region throughout the fourth and fifth months, depending, apparently, 

 upon the amount of fulness in the subdermal connective tissue. The helix of this 

 specimen is characterized by the presence of a moderately well developed tuber- 

 culum (Darwinii). In the next specimen (fig. 45) the helix shows a distinct crown 

 angle (satyr-tip), which doubtless would have persisted in the adult. Although 

 the concha is still not much more than a cleft, one can make out the presence of a 

 plica principalis near its upper end. The condition shown in figure 46 is an inter- 

 esting example of the flat type of auricle with a prominent tuberculum. The 

 tendency toward obliteration of the helix appears to be due partly to the surplus 

 tissue in the region of the anthelix, which is thrown into corresponding transverse 

 folds. In figure 47 the transverse folds are absent and in their stead is a prominent 

 plica principalis. The auricle shown in figure 48, although of the same size as its 

 neighbors, is of a more rudimentary type and resembles the specimen in figure 39. 

 It is probable that both of these would have resulted in small ears had the fetuses 

 gone on to term. 



Figure 49 shows a marked development of the transverse folds in the region 

 of the anthelix, which were first described by Schwalbe and interpreted by him as 

 temporary representatives of the longitudinal folds seen in some of the long-eared 

 mammals. The fact that they are so irregular in occurrence, however, as can be 

 seen by this and the next plate, makes it doubtful whether these folds can be safely 

 interpreted as phylogenetic rudiments. I am inclined rather to attribute them to 

 a redundancy of the soft tissues of the anthelix. This specimen illustrates very 

 well the difference in character between the auricular derivatives of the mandibular 



