The occurrence and position of the ”connecting sac” in the nasal tract complex of small odontocetes (Mammalia, Cetacea)

The aspects of the “connecting sac” are studied in Lagenorhynchus albirostris, Lagenorhynchus obliquidens, Lagenorhynchus acutus, Tursiops truncatus, Delphinus delphis, Phocoena phocoena, Sotalia guianensis, Stenella coeruleoalba and Stenella frontalis. Comparing the development of the connecting sac in the various species it is found that there are great variations. These variations are also found in the various individuals of the same species. For this reason the importance of this structure in soundproduction is open to doubt. The development of the connecting sac seems to be related to the development of the posterior part of the naso-frontal sac in such a way that, when a large and well developed posterior part of the naso-frontal sac is present, the connecting sac is small. The extreme situation is found is Phocoena phocoena where the posterior part of the naso-frontal sac is very large, while the connecting sac is often found to be reduced or completely absent.