DEVELOPMENT OF THE AURICLE IN THE HUMAN EMBRYO. 115 



however, he finds six. There are two hillocks on the mandibular arch, the lower 

 one becoming the tragus, the upper becoming the spina helicis. At the upper end 

 of the first gill-cleft is the colliculus intermedius, which forms all of the helix with 

 the exception of the spina. On the hyoid arch he finds three hillocks, the upper one 

 becoming the anthelix and the next lower the antitragus; the lowest one seems to 

 disappear and become covered in by the tragus. 



His (1885), in describing the development of the ear, gives a classical account 

 of the auricular hillocks (or tubercles, as he names them) which has dominated all 

 subsequent literature. He describes the auricle as arising from the nodular edges 

 that surround the first gill-cleft, very early showing a subdivision into six hillocks, 

 which he numbers consecutively 1 to 6. He divides the mandibular arch into a 

 dorsal and a ventral portion. On the ventral portion is the first hillock (tuberculum 

 tragicum). The remainder of this portion takes no further part in the formation 

 of the auricle, becoming the lip-ridge and jaw-ridge, the latter subsequently covering 

 in and fusing with hillock 6. Hillocks 1 to 5 form a plump ring surrounding the 

 first gill-cleft, which thus becomes the fossa angularis. In this process hillocks 

 1 and 2, also 2 and 3, partially fuse. Between 3 and 4 there is a deep furrow; 3 is 

 continued as a tail caudal to 4 and loses itself in the neighborhood of hillock 6. The 

 eventual helix is formed by the union of hillocks 2 and 3, together with the tail-like 

 process extending from the latter. The anthelix is derived from hillock 4, the 

 lobule from hillock 6. The taenia lobularis is a remnant of 6. The tragus is 

 derived from hillock 1 , the antitragus from hillock 5. In addition to these hillocks, 

 the author describes a tuberculum centrale, which takes the form of a transverse 

 elevation in the floor of the fossa angularis, separating the upper and lower depres- 

 sions. It consists of a connective-tissue pillow or swelling of the closure plate of 

 the first gill-cleft. The cartilaginous strand belonging to the second arch extends 

 into it. It contains a small blood-vessel, the stapedius artery. The furrow between 

 hillocks 1 and 5 he designates as the sulcus antitragicus, while the lower end of the 

 fossa angularis he calls the incisura intertragicus. The crus, or spina helicis, is 

 derived from a fusion of hillocks 2 and 4. 



Kastschenko (1887), in a study of the fate of the mammalian gill-clefts, in 

 which he concerns himself particularly with the thymus and thyroid, describes 

 the external auditory canal of the pig, which, he points out, is a secondary formation, 

 its tip only being a true remnant of the first epidermal pocket. He pictures five 

 auricular hillocks, as seen in 12, 13, and 15 mm. specimens, but does not clearly 

 trace them into the eventual ear. Kastschenko 's figures correspond fairly well 

 with the description given by His for the human, with the exception of the fifth 

 and sixth tubercles. Kastschenko's hillock 5 seems to correspond to His's hillock 6. 



Tartaroff (1887) reports a relationship between the character of the skin and 

 the underlying cartilage covering the auricle, particularly as to the presence of hair 

 and subcutaneous fat. The growth of the cartilage results in tension of the skin, 

 which he regards as the cause (pressure atrophy) of the lack of fat and the disappear- 

 ance of hair, and it is inferred that the resistance of the skin may explain the folding 

 of the ear cartilage. 



