the second their exit is easy because of the air that pushes them by jostling when it exits with the force of blowing. bones were needed in the structure of the nose because if it were made of two organs like flesh it would be exposed to blockage if its top were to fall on its bottom. if it were made of an organ of medium softness like cartilage and its mass was made thin it would be prepared for crushing easily and if its mass was made thick it would be heavier. as for the bones due to their hardness the thin ones are as strong as the thick ones of cartilage with lightness. it was created from two bones because if it were one bone it would be prepared for the spread of corruption that might occur to a part of it. if it were made of many bones its structure would be very weak because of the thinness of its mass. it was created from two triangular bones because its shape must be such that the air takes from a wide area and ends up narrow as in the fennel so that the air penetrates the two holes that exit it strongly because of the narrowness of the space for it in them. this is only the case if the two bones are triangular.
وثانيهما أن خروجهما يكون سهلا بسبب الهواء الذي يدفعها بالمزاحمة عندما يخرج بقوة النفخ، واحتيج في تركيب الأنف إلى عظام لأنه لو كان من عضولين كاللحم لكان يعرض للانسداد لو قوع أعلاه على أسفله، ولو كان من عضو متوسط اللين كالغضروف وجعل جرمه رقيقا تهيأ للارتضاض بسهولة وإن جعل جرمه غليظا أثقل وأما العظام فلصلابتها يكون الرقيق منها في قوة الغليظ من الغضاريف مع الخفة. وخلق من عظمين لأنه لو كان عظما واحدا كان متهيئا لسريان الفساد العارض لجزء منه. ولو كان من عظام كثيرة لكان تركيبه ضعيفا جدا لأجل رقة جرمه، وخلق من عظمين مثلثين لأن شكله يجب أن يكون بحيث يأخذ الهواء من سعة وينتهي إلى ضيق كما في الباذهنج وذلك ليكون نفوذ الهواء في الثقبين النافذين منه نفوذا قويا لأجل ضيق المكان عليه عندهما. وإنما يكون كذلك إذا كان العظمان مثلثين.