Abstract
The article deals with a passage of the famous Appendix Probi, i.e. the fifth fragment of the text immediately following Ps. Probus’ Instituta artium, which contains a precious antibarbarus, presumably written around the middle of the 5th century CE; the Appendix is located in the final portion of the codex Neapolitanus 1 (7th century CE) and its correct interpretation is notoriously very difficult because of the many damages suffered by the manuscript. The passage at issue, after may at-tempts, is read nowadays obst<etri>x non ossetrix; the late Latin assimilation /ps/ > /ss/ is here commented with particular reference to chronology, in the light of the available sources. The presence of the assimilation is corroborated by a new reading of a tachygraphical gloss, which was originally written to the left of the main text: obs(t)etrix, nam ab ossequio dicitur. Interestingly, this new proposal shows a pareti-mology of the lemma, that confirms not only the disputed reading obst<etrix> non ossetrix in the Appendix, but also provides a key to interpret more accurately the regressive assimilation /ps/ > /ss/