Desmognathous, without basipterygoid processes; with one pair of sternotracheal muscles.
Order Anseriformes.-Desmognathous, nidifugous; with two pairs of sterno-tracheal muscles, with complete basipterygoid processes and with a penis.
Aegithognathous, without basipterygoid processes.
MESITEs.-Without basipterygoid processes, and with large spina interna.
Without basipterygoid processes.
In many birds the basisphenoids send out a pair of basipterygoid processes by which they articulate with the pterygoids.
They are typically nidifugous; the simple structure of their neossoptiles; quintocubital; compound rhamphotheca; holorhinal nares imperviae; basipterygoid processes; simple articular facet of the quadrate; configuration of the palatal bones, including the large vomer; incisura ischiadica; simple hypotarsus; the thigh muscles; the copulatory organ.
Opisthocomi.-Arboreal, with long spina externa; without basipterygoid processes.