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Summary
Frog narial closure does not use intrinsic muscles. Instead, the M. submentalis, a lower jaw muscle, facilitates this action, confirmed by electromyography and airflow measurements.
Area of Science:
- Herpetology
- Comparative anatomy
- Biomechanics
Background:
- Narial closure mechanisms in anurans (frogs) are not fully understood.
- Previous hypotheses suggested intrinsic muscles might be involved.
Purpose of the Study:
- To investigate the muscular basis of narial closure in frogs.
- To test Gaupp's hypothesis regarding the role of the M. submentalis.
Main Methods:
- Examination of over 40 frog species for narial musculature.
- Electromyography of relevant muscles during simulated narial closure.
- Measurement of airflow at the nostrils concurrently with muscle stimulation.
Main Results:
- No intrinsic narial muscles were found to be involved in narial closure across examined species.
- The M. submentalis (lower jaw muscle) was identified as the primary muscle responsible for narial closure.
- Muscular displacement of the M. submentalis was shown to transmit forces via the snout's skeletal and cartilaginous structures.
Conclusions:
- Narial closure in frogs is exclusively achieved through the action of the M. submentalis.
- Skeletal and cartilaginous elements of the frog snout play a crucial role in transmitting force for narial closure.
- The findings support and confirm Gaupp's long-standing hypothesis on anuran narial closure mechanics.