150 THE STRUCTURE OF MAN 



region of the human eyebrow recall from their position the 



feelers [or supra-orbital vibrissae] of the lower Mammals. They 



have been already dealt with (ante, p. 4). 



A well-marked variation of the upper eyelid, apparently due 

 to arrested development during fcetal 

 life, is that resulting in the formation 

 of the so-called epicanthus (ep., Fig. 

 93). This, as its name suggests, is a 

 prolongation of the lid, which extends 

 more especially over the inner angle 

 of the eye. In certain races, such as 

 the Mongolian, this variation is con- 

 spicuous, giving rise to the slit -like 

 appearance and oblique position of the 

 aperture of the eye. The obliquity, 

 however, is only apparent, for it 



FIG. 93. EYE OF A MONGOLIAN, vanishes if the skin above the nose 

 WITH THE EPICANTHUS (ep.). be tightly stretched. The epicanthus, 



(After Merkel.) 



as it appears in the Japanese, has been 



very exactly described by Balz, who points out that it results 

 from the flatness of the bridge of the nose the superfluous skin 

 forming the fold in question. It is a matter of interest that a 

 similar condition has been observed among Caucasian children. 

 According to Kanke, about 6 per cent of these exhibit a markedly 

 Mongolian type of eye during the first six months of their lives. 



THE AUDITORY ORGAN 



In describing the skeleton of the head, mention has been made 

 (ante, p. 49) of the post-oral branchial sacs which characterise 

 a certain embryonic stage, and of the auditory ossicles (p. 64). 



The latter arise partly from the original suspensory apparatus 

 of the lower jaw, i.e. from the visceral skeleton? As to the 

 former, only the anterior sac persists in Mammals ; and from 

 this (the spiraculum l of the lower Fishes) the cavity of the middle 

 ear (Eustachian tube and tympanic cavity) develops. 



1 [Considerable interest attaches to the fact that the only living Vertebrates in 

 which this, the " hyo-branchial cleft " of comparative embryologists, is absent, are the 

 Marsipobranchii (Lampreys and Hags) and the Teleostean or Bony Fishes. Its occur- 

 rence in the embryos of the former group is now well known (Shipley, Qu. Jour. Micr. 

 Sci., vol. xxvii. p. 349), and Sagemehl has described its apparent vestige in certain 

 adult members of the latter (Morpholog. Jahrb., Bd. ix. p. 213). It is, however, in- 

 sufficiently recognised that the painstaking researches of Ramsay Wright have 



