The study of the language in which the ancient documents of la Franja were written is of vital importance to the knowledge of the history of the Catalan language in this region of Aragon. Clearly, the formulaic language that is found in these and the homogeneity of the script are limitations of these manuscripts when it comes to finding truly dialectic elements, given that, in them, spontaneity is limited to a minimum; in fact, readers examining these documents may find that a sort of script exists, coinciding in other texts of the same era and from distinct areas. However, its study corroborates that there are indeed diatopically marked elements, even in the medieval synchrony in which they were written. In these pages, we shall analyze the lexical peculiarities of some manuscripts from Matarraña (Teruel) from the 14th and 15th centuries, clearly Western and mainly attested to in documents produced in the Valencian area or in the North-west. We also present the registered aragonisms and those words that have not been found in any other area.