[The problem of yawning in reptiles].

Yawning in reptiles was investigated in field observations of various lizard and tortoise species and in laboratory experiments with the tortoises Testudo h. hermanni and Emys orbicularis. In the experiments the animals' reactions to various conditions of temperature, air O2 and CO2 content, fatigue and hunger, were tested. Yawning and related or similar motor patterns are described and discussed.