Muscles of mastication and the temporo-mandibular joint of the Saimaa (Pusa hispida saimensis) and Baltic (Pusa hispida botnica) ringed seals.

As part of our research aiming to understand the morphological variation in ringed seals, we dissected mastication muscles of nine Saimaa ringed seals and two Baltic ringed seals. We found no significant differences in the muscles of mastication between these subspecies but the location of the tympanic bulla in relation to the articular surface of the temporomandibular joint was more medial in the Saimaa ringed seal. As compared with the previously studied Baikal and Caspian seals, the origin of the jaw-opening digastricus muscle covered less of the tympanic bulla in the Saimaa and Baltic ringed seals. Our data on masticatory-muscle masses indicated that similarly to terrestrial mammal species, the growth patterns of mastication muscles of the Saimaa ringed seal differed from each other according to the body size.