150 THE STRUCTURE OF MAN 
region of the human eyebrow recall from their position the 
feelers [or supra-orbital vibrissze] 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 fecetal 
life, is that resulting in the formation 
of the so-called epicanthus (ep., Fig. 
93). This, as its name suggests, is a 
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 sht-hke 
appearance and oblique position of the 
aperture of the eye. The obliquity, 
i however, is only apparent, for it 
Re GEL elisa Se Monona vanishes if the skin above the nose 
WITH THE Epicantaus (¢p.). be tightly stretched. The epicanthus, 
(After Merkel.) 5 ; 
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 Ranke, 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 ! of the lower Fishes) the cavity of the middle 
ear (Hustachian 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 oceur- 
rence in the embryos of the former group is now well known (Shipley, Qu. Jour. Mier. 
Sct., vol. xxvii. p. 849), 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 
prolongation of the lid, which extends — 
