That Moses imposed [his] hand upon the head, I doubt nothing. For although it is not [expressly] stated, yet from all the others by which some good is conferred, this can be conjectured — [namely] that in all [of them] hands are imposed upon the head; and therefore below (v. 23), where in Hebrew it is read only “he put [his] hands upon him,” our Interpreter clearly said that “Moses imposed hands upon the head of Joshua.” But the manner was, that both hands were joined [together], as [is] also the custom of the other modes; and the Hebrew word imports [it]: סמך [samakh]. Others refer that conjunction to the head — namely Oleaster, [understanding] that the hands were joined to the head. Yet either [sense] — both the conjunction of the hands among themselves, and their conjunction to the head — can be taken. For it can happen otherwise, that one hand be imposed after the other; or [that] both indeed [be imposed] and joined, but so that [they be] held aloft in the air above the head, not upon the head — if with Valla one is pleased to distinguish these. But now, both hands, extended, touch the top of the head, and, as it were, rest upon it. But whether Joshua ought then to have been with knees bent, or [whether] he indeed stood, but bending [his] head very much, I affirm nothing. In either manner, however, he bore [himself with] the highest modesty and religion. In ch. 4 [of the tractate] Hilkhot Sanhedrin, in Rambam [Maimonides] (vol. 4, last book), it is taught that [there] ought to be some one of all the Judges [who is] סמוך [samukh, “ordained”], as Moses our minister; [and Moses] סמך [samakh, “laid hands on / ordained”] Joshua; and the same [Moses] סמך also the 70; and the majesty of God appears over them, which is wont to be called שכינה [Shekhinah]. And so these [ordained] others, סמך, until it ceased — סמיכה [semikhah] — that is, they no longer imposed hands upon the head, but only said: “Thou art Rabbi” — סמוך samukh. Nay, even of him who is the associate of the Rab himself, or of the Doctor, the Jews are also wont to say לסמוך [lismokh], or, “They had given him” סמיכות [semikhut] or סמיכה [semikhah] — as [David de Pomis] notes in his Tzemach David (p. 152); and Elias in Tishbi under—
(col. 195)
…[under] the word chabor; who also, at the word samach, teaches that this ceremony was drawn from that example of Moses — as also R. Abraham Zacuth (fol. 60), and my former Rabbinus (ch. 21), where also [something] is noted concerning the words which used to be added at the same time from a solemn formula.