and it was also created at the end of the cartilaginous hump to preserve the position of that hump and to make the eyelash implant solid for the benefits that we mentioned. and this eyelid is much smaller than the upper one because if it were as large as the upper one it would trap the nourishment that is between it and the eyeball. and the upper one is not like that because its movement pushes the dirt and what is towards it downwards so the dirt appears and comes out. and the eyelash of the lower eyelid is turned downwards because if it were erect in a straight line it would prevent the descent of what falls on it of dust and the like and would trap it in front of the eyeball. and if it were erect upward it would harm the sight. therefore it was created turned downwards because that is more preventing the ascent of what is meant to ascend to the eyeball.
وخلق أيضا في طرف عطفة الجرم الغضروفي ليحفظ وضع ذلك العطف وليكون مغرس الهدب صلبا لما نذكره من منافع ذلك وهذا الجفن أصغر كثيرا من العالي لأنه لو كان عظيما كالعالي لحبس الغذى الذي بينه وبين المقلة ولا كذلك العالي فإن حركته تدفع القذى والذي نحوه إلى أسفل فيظهر القذى ويخرج وهدب الجفن الأسفل منقلبة إلى أسفل لأنها لو كانت منتصبة على الاستقامة لمنعت نزول ما ينزل عليها من الغبار ونحوه وحبسته أمام المقلة، ولو كانت منتصبة إلى فوق لأضرت بالإبصار فلذلك خلقت منعطفة إلى أسفل فإن ذلك أمنع لتصعد ما من شأنه التصعد إلى المقلة.