the benefit of its division or mixing its division so that they become one section is that one of the two sections passes through the inside of the collarbone and the other through its outside so the nourishment reaches both its outside and inside and that is something that would not be possible if they were one section. what passes through the outside of the collarbone needs to go around it so that the nourishment reaches many parts between the outside of the collarbone but what passes through its inside does not need that because the inside of the collarbone does not need that due to the many veins there. then if that purpose is achieved the two sections return and become one vein because that is what was intended by them before the division.
وفائدة انقسامه أو لا اختلاط قسمته حتى يكون منهما قسم واحد أن يمر أحد القسمين بباطن الترقوة، والآخر بظاهرها فيعم الغذاء لظاهرها وباطنها وذلك مما لا يتم لو كانا قسما واحدا، والذي يمر بظاهر الترقوة ويحتاج أن يستدير عليها ليصل منه الغذاء إلى أجزاء كثيرة بين ظاهر الترقوة وإنما لم يحتج إلى ذلك المار بباطنها لأن باطن الترقوة يستغني عن ذلك بكثرة العروق هناك ثم إذا تم ذلك الغرض عاد القسمان فصارا عرقا واحدا لأن ذلك هو المقصود منهما قبل القسمة.