138 DEVELOPMENT OF THE AURICLE IN THE HUMAN EMBRYO. 



DESCRIPTION OF PLATES. 



Plate 1. 

 Ventrolateral view of the head in a series of human embryos, showing the change in topography of the auricle 

 in the course of its development. The surface area of the mandibular and hyoid bars entering into the formation of 

 the auricular primordium is colored blue. These figures show the lateral and dorsal migration of the auricle coincident 

 with the formation of the mandible. 

 Fio. 9. Drawing made directly from an embryo 6 mm. long, No. 1787 Carnegie Collection. X 22. The olfactory 



disk and the lens of the eye are outlined by dots. 

 Fio. 10. Reconstruction model of an embryo 12 mm. long, No. 1121 Carnegie Collection. X 15. 

 Fig. 11. Reconstruction model of an embryo 14 mm. long, No. 940 Carnegie Collection. X 15. Here the parts 



belonging to the jaw are clearly separated from what are to be the soft parts of the upper neck by a 



groove, which might be called the mental groove. 

 Fig. 12. Reconstruction model of an embryo 18 mm. long, No. 1390 Carnegie Collection. X 12.3. 



Plate 2. 

 Drawings of human embryos, showing the region of the first branchial cleft and its transformation into a fossa 

 angularis. Coincident with this transformation the mesenchyme of the hyoid and mandibular bars undergoes prolif- 

 eration and becomes condensed to form the primordium of the auricle. Foci of more active proliferation show on the 

 surface as branchial hillocks. Specimens are from the Carnegie Collection. 



Fig. 13. No. 1380, 5 mm. long. X 34. Fig. 16. No. 562, 13 mm. long. X 20. 



Fig. 14. No. 1767, 11 mm. long. X 24. Fig. 17. No. 1232, 14 mm. long. X 17. 



Fig. 15. No. 1461, 10 mm. long. X 20. Fig. 18. No. 475, 15 mm. long. X 17. 



Plate 3. 

 Drawings of human embryos, in series with the preceding plate, and showing the disappearance of the branchial 

 hillocks and the completion of the auricle in its primary form. Specimens are from the Carnegie Collection. 



Fig. 24. No. 955, 17 mm. long. X 24. 

 Fig. 25. No. 1584, 18 mm. long. X 24. 

 Fig. 26. No. 1134e, 21.3 mm. long. X 24. 

 Fig. 27. No. 13586, 33.2 mm. long. X 24. 



Plate 4. 

 Photographs of the auricle of the human fetus during the third month, all being taken at an enlargement of 

 10 diameters. In some cases the right ear was selected and reversed for convenience in comparison. These are 

 indicated by the letter R. All specimens are from the Carnegie Collection, and length given is crown-rump. 



Fig. 35. No. 2170, 50 mm. 



Fig. 36. No. 2095, 52 mm. (R.) 



Fig. 37. No. 2095, 52 mm. 



Fig. 38. No. 2066, 53 mm. (R.) 



Fig. 39. No. 2079, 56.5 mm. 



Fig. 40. No. 1561, 57 mm. 



Fig. 41. No. 218, 62.5 mm. (R.) 



Plate 5. 

 Photographs showing changes occurring in the auricle of the human fetus during the fourth month. In some 

 cases the right ear was selected and reversed for convenience in comparison. These are indicated by the letter R. 

 All the photographs are taken at an enlargement of 6 diameters. Specimens are from the Carnegie Collection, and 

 length given is crown-rump. 



Fig. 47. No. 1449, 87.3 mm. 

 (R.) Fig. 48. No. 2003, 103.5 mm. 



Fig. 49. No. 1858, 100 mm. (R.) 

 Fig. 50. No. 2274, 113 mm. (R.) 



Plate 6. 

 Photographs showing the form of the human auricle during the fifth month of intrauterine life, with the exception 

 of specimen shown in figure 59, which has a menstrual age of 23 weeks. The photographs are all shown at an enlarge- 

 ment of 4 diameters. Specimens are from the Carnegie Collection, and length given is crown-rump. 

 Fig. 51. No. 2185, 113.5 mm. Fig. 56. No. 1782, 135.6 mm. 



Fig. 52. No. 9526, 114 mm. Fig. 57. No. 1702, 150 mm. 



Fig. 53. No. 1811, 114 mm. Fig. 58. No. 1708, 154 mm. 



Fig. 54. No. 1716, 119 mm. Fig. 59. No. 1742, 191.2 mm. 



Fig. 55. No. 19576, 119 mm. 



