以下日本語版の「ウィキペディア」の解説の要点を箇条書きにしたものとなる。
・上睫毛は反り返るように曲がる。
・上睫毛は4～5の（不完全な）列で、下睫毛は2～3列で成長する。
・上睫毛の数は約300～400本、下睫毛は100～150本となる。
・上睫毛は10～20本ごとに三角形状の毛根のグループを成す。
・長さは上睫毛で、一般的に8～12㎜、下睫毛が6～8㎜となる。
・睫毛の成長期間は平均で34日程度となる。
・生え変わり周期はだいたい90日程度となる。
以下は「Wikipedia」の解説文となる。
An eyelash (also called lash) (Latin: Cilia) is one of the hairs that grows at the edge of the eyelids. It grows in one layer on the edge of the upper and lower eyelids. Eyelashes protect the eye from debris, dust, and small particles and perform some of the same functions as whiskers do on a cat or a mouse in the sense that they are sensitive to being touched, thus providing a warning that an object (such as an insect) is near the eye (which then closes reflexively). The eyelid margin from which lashes grow is among the most sensitive parts of the human body, with many nerve endings enveloping the lashes, giving it sensitivity to light touch,[1] enabling it to trigger the blink reflex when touched.[2]
The Ancient Greek word for eyelash is βλέφαρον (transliterated as blepharon), which is seen as a root in biological terms like Blephara.
Development[edit]
The eyelashes of the human embryo develop from the ectoderm[3] between the 22nd and 26th week of pregnancy.[4] Natural eyelashes do not grow beyond a certain length, and fall off by themselves without any need for trimming. Eyelashes take about seven to eight weeks to grow back if pulled out, but constant pulling may lead to permanent damage. Their color may differ from that of the hair, although they tend to be dark on someone with dark hair and lighter on someone with light hair. Eyelash hair is not androgenic[5] and is therefore not affected by puberty. Lash follicles do not have an arrector pili muscle associated with them, making the lashes static.[6]
Length and Thickness[edit]
Human lashes do not vary in length by gender[7] or ethnicity,[8] with the upper lashes of humans typically 7 to 8 mm in length,[7] and generally do not exceed 10 mm in length.[9] Lower lashes average between 5 and 6 mm in length.[7] Eyelashes are considered to be long when they are 10 mm or greater in length.[10] Human eyelash length, thickness, and darkness decrease significantly with age.[11]
People of Asian ethnicities have significantly thicker lashes than people of Caucasian ethnicities.[8] However, the number of lashes on the eyelids is fewer in Asians than in Caucasians.[8]
Curvature[edit]
Eyelashes grow outwards from both upper and lower eyelids, with varying degrees of curl. People of Caucasian ethnicities have lashes that are more curled than those of Asian ethnicities.[8] However, the degree of curling vary significantly even within a population or ethnicity, where people of Asian ethnicities can also exhibit naturally highly curled lashes.[12]
Density[edit]
The number of individual lashes on the upper eyelid is typically 90 to 160, and on the lower eyelid 75 to 80.[1] The number of follicles and hence lashes cannot be increased after birth because all follicles develop during embryogenesis.[6]
Glands[edit]
The follicles of eyelashes are associated with a number of glands known as the glands of Zeis and the glands of Moll.
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