he said and he created it with two membranes like the arteries. he means with two layers. and he was created thus so that its body would be smooth and its pores very narrow so that only very fine blood seeps out of it. and what seeps out of it encounters a lot of air spread out in the cavities of the lungs so it mixes with it and thus it becomes suitable to become a spirit in the heart. and the rest of the blood that does not seep out of those pores passes through the openings of the parts of this vein so the lung is nourished by it. therefore the nourishment of the lung is only what remains of the parts of this vein after its fine blood has been sifted into the cavities of the lungs.
قوله وقد خلق ذا غشائين كالشريانات. يريد ذا طبقتين وإنما خلق كذلك ليكون جرمه مستحصفا ضيق المسام جدا فلا يرشح منه من الدم إلا ما لطف جدا، وهذا لذي يرشح منه يصادف هواء كثيرا مبثوثا في تجاويف الرئة فيختلط به وبذلك يصلح لأن يصير في القلب روحا وباقي الدم الذي لا يرشح من تلك المسام ينفذ من فوهات أجزاء هذا العرق فتغتذي به الرئة فلذلك غذاء الرئة إنما هو ما تبقى من أجزاء هذا العرق بعد ترشيح لطيفه إلى تجاويف الرئة.