Development of the external ear in the dachs rabbit

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Abstract
Development of that part of the external ear which protects the external auditory meatus appears to be similar in all animals since the hillocks of His have been described for reptiles, amphibia, and birds as well as mammals. Disagreement exists as to the origin and fate of the various hillocks, especially tragus and antitragus. Most observations of the developing ear have begun with the formation of the hillocks at which time the tragus is situated on the mandibular arch. Because of the rapid early growth, transitional steps from the open branchial groove to this stage have not been described previously. The retarded growth of the dachs rabbit makes it possible to see intermediate steps. Here it is shown that the entire auricle arises from an intact and continuous primordium, with the tragus arising from the hyoid arch and migrating to the mandibular bar in the normal course of cell proliferation and differentiation. Variations in normal and heterozygous animals can be found in the relative rates of development of the surrounding areas.