Heidegger's Bible Handbook: Old Testament in General: Minor Divisions
5. The minor Sections, open and closed. Finally, the Minor Sections are either פתוחות/open, or סתומות/closed. The former are noted with the letter פ, but the latter with the letter ס. Concerning the sections of this sort, and the account of the same, the Rabbis have various opinions, which the Celebrated Buxtorf reviews in his Libero de Abbreviaturis. Now, a section is called open, because it begins at the beginning of the line: but closed section, which is also called סמוכה/conjoined, is thus denominated, because that little space, in the midst of which is ס, is closed at both ends on the same line. Because the Hebrews believe that these sections were instituted by Moses himself, they religiously mark and observe them in the Book of the Law, of which they make use in their Synagogues: although they are of an altogether doubtful origin, and, since they have no use today, were not with good reason omitted by Munster, and by others, as Rabbinic figments.
 Johann Buxtorf, Sr. (1564-1629) was a renowned Reformed Hebraist, known as the “Master of the Rabbis”. He served as Professor of Hebrew at Basel from 1590 to 1629.
 Sebastian Munster (1489-1552) was a German scholar of great talent in the fields of mathematics, Oriental studies, and divinity. He joined the Lutherans, became Professor of Hebrew at Basil, and produced important early Reformation commentaries on the Old Testament (Annotationes in Vetus Testamentum) and on Matthew (Annotationes in Matthæi Evangelium Hebraicum).