Exodus 29:20

תנוך — This is the inner cartilage which is within the ear, which they call tendrons in old French (cf. Rashi on Leviticus 14:14). בהן ידם — i. e. the thumb; and the blood was placed on the middle joint (Chullin 11a).

וְשָׁחַטְתָּ֣ אֶת־הָאַ֗יִל וְלָקַחְתָּ֤ מִדָּמוֹ֙ וְנָֽתַתָּ֡ה עַל־תְּנוּךְ֩ אֹ֨זֶן אַהֲרֹ֜ן וְעַל־תְּנ֨וּךְ אֹ֤זֶן בָּנָיו֙ הַיְמָנִ֔ית וְעַל־בֹּ֤הֶן יָדָם֙ הַיְמָנִ֔ית וְעַל־בֹּ֥הֶן רַגְלָ֖ם הַיְמָנִ֑ית וְזָרַקְתָּ֧ אֶת־הַדָּ֛ם עַל־הַמִּזְבֵּ֖חַ סָבִֽיב׃

Then shalt thou kill the ram, and take of its blood, and put it upon the tip of Aharon’s right ear, and upon the tip of the right ear of his sons, and upon the thumb of their right hand, and upon the great toe of their right foot, and sprinkle the blood upon the altar round about.