§2.15.1Αἱ δʼ ὀφρύες καὶ αἱ βλεφαρίδες ἀμφότεραι βοηθείας χάριν εἰσίν, αί μὲν ὀφρύες τῶν καταβαινόντων ὑγρῶν, ὅπως ἀποστέγωσιν οἷον ἀπογείσωμα τῶν ἀπὸ τῆς κεφαλῆς ὑγρῶν, αἱ δὲ βλεφαρίδες τῶν πρὸς τὰ ὄμματα προσπιπτόντων ἕνεκεν, οἷον τὰ χαρακώματα ποιοῦσί τινες πρὸ τῶν ἐργμάτων.
The eyebrows and the eyelashes are both for the sake of protection: the eyebrows for the sake of the fluids that flow down, so that they may shelter the eyes like the eaves of a roof from the fluids coming from the head; the eyelashes for the sake of things that fall towards the eyes, just as some people build palisades in front of enclosures.
§2.15.2εἰσὶ δʼ αἱ 2 μὲν ὀφρύες ἐπὶ συνθέσει ὀστῶν, διὸ καὶ δασύνονται πολλοῖς ἀπογηράσκουσιν οὕτως ὥστε δεῖσθαι κουρἀς, αἱ δὲ βλεφαρίδες ἐπὶ πέρατι φλεβίων· ᾗ γὰρ τὸ δέρμα περαίνει, καὶ τὰ φλέβια πέρας ἔχει τοῦ μήκους.
And the eyebrows are situated on the junction of the bones, which is why in many people, as they grow old, they become so shaggy as to require shearing; whereas the eyelashes are at the extremity of the small veins; for where the skin terminates, the small veins also reach the limit of their length.
ὥστʼ ἀναγκαῖον διὰ τὴν ἀπιοῦσαν ἐκμάδα σωματικὴν οὐσαν, ἄν μή τι τῆς φύσεως ἔργον ἐμποδίσῃ πρὸς ἄλλην χρῆσιν, καὶ διὰ τὴν τοιαύτην αἰτίαν ἐξ ἀνάγκης ἐν τοῖς τόποις τούτοις γίνεσθαι τρίχας.
Consequently, because the moisture which passes off is of a corporeal nature, unless some work of nature prevents it for some other use, and owing to this kind of cause, it is necessary that hair should grow in these places.