[The development of the vertebrate skull (author's transl)]

The greater metabolic demands for oxygen in warm-blooded animals led to the separation of the upper respiratory tract from the digestive during development and the evolution of a "respiratory skull." The sphenoid sinus originated from the posterior divisions of the nasal cavity, and adapted itself functionally to the other pneumatic cavities. The latter represent inversions of the main nasal cavity and are found only in mammals. The "respiratory skull" is considered to be not only a clinical nosologic entity but also a development step of vertebrate skull formation.