Four cranial bones (supraethmoid, glossohyal, premaxilla, vomer) of nine-month-old reciprocal hybrids of Salmo salar and Salmo trutta and the arrangement of the opercular bones in reciprocal hybrids aged from 4 to 24 months were analyzed. The supraethmoid bone in the majority of the hybrids studied was similar to that of salmon. In some hybrids, an atypical additional process was found on the lower part of the supraethmoid bone. The large process of the premaxilla bone had a short base in the two groups of hybrids as in salmon, and it was low as in trout. The shape of the vomer plate was intermediate between a triangle (as in trout) and a pentagon (as in salmon) in the majority of salmon x trout hybrids and almost half of the trout x salmon hybrids. The glossohyal in some hybrids had an uneven number of teeth in each row, and these rows of teeth were uneven.
