The Vedanta Sutras of Badarayana, Commentary by Sankara (SBE38), tr. by George Thibaut  at sacred-texts.com
17. (There takes place) a lighting up of the point of its (the soul's) abode (viz. the heart); the door (of its egress) being illuminated thereby; owing to the power of knowledge and the application of meditation to the way which is part of that (knowledge); (the soul) favoured by him in the heart (viz. Brahman) (passes upwards) by the one that exceeds a hundred (i.e. by the hundred and first vein).
Having absolved the inquiry into a point of the higher knowledge into which we were led by a special occasion, we now continue the discussion connected with the lower knowledge.--It has been stated that up to the beginning of the way the departure of him who knows and him who does not know is the same. The present Sûtra now describes the soul's entering on the way. The abode of the soul, when--having taken within itself speech and the other powers--it is about to depart, is the heart, according to the text, 'He taking with him those elements of light descends into the heart' (Bri. Up. IV, 4, 1). Of the heart the point becomes lighted up, 'and subsequent to that is the departure of the soul, starting from the eye or some other place, according to the passage, 'The point of his heart becomes lighted up, and by that light the Self departs, either through the eye or through the skull or through other places of the body' (Bri. Up. IV, 4, 2). The question here arises whether that departure is the same for him who knows and him who does not know, or if there is a special limitation in the case of the former; and the prima facie view might be upheld that there is no such limitation since scripture records no difference. Against this the teacher states that although, equally for him who does know and him who does not know, the point of the heart becomes shining and the door of egress thereby
is lighted up, yet he who knows departs through the skull only, while the others depart from other places.--Why so?--'On account of the power of knowledge.' If also he who knows departed, like all others, from any place of the body, he would be unable to reach an exalted sphere; and then all knowledge would be purportless. 'And on account of the application of meditation on the way forming a part of that.' That means: in different vidyâs there is enjoined meditation on the soul's travelling on the way connected with the vein that passes through the skull;--which way forms a part of those vidyâs. Now it is proper to conclude that he who meditates on that way should after death proceed on it 1. Hence he who knows, being favoured by Brahman abiding in the heart on which he had meditated, and thus becoming like it in nature departs by the vein which passes through the skull and 'exceeds the hundred,' i.e. is the hundred and first. The souls of other men pass out by other veins. For thus scripture says, in a chapter treating of the knowledge of Brahman dwelling in the heart, 'There are a hundred and one veins of the heart; one of them penetrates the crown of the head; by that moving upwards a man reaches immortality; the others serve for departing in different directions' (Kh, Up. VIII, 6, 5).
378:1 For otherwise the meditation enjoined would be 'adrishtârtha' only; an alternative not to be admitted anywhere as long as a 'seen' purpose can be demonstrated.