The quadrate is invariably a conspicuous bone and movably articulating with the cranium and by a special process with the pterygoid.
1, A, B, mn), articulating at their bases with the head-capsule by sub-globular condyles, and provided with abductor and adductor muscles by means of which they can be separated or drawn together so as to bite solid food, or seize objects which have to be carried about.
A diagnosis covering all the Ratitae (struthio, rhea, casuarius, dromaeus, apteryx and the allied fossils dinornis and aepyornis) would be as follows - (i) terrestrial birds without keel to the sternum, absolutely flightless; (ii) quadrate bone with a single proximal articulating knob; (iii) coracoid and scapula fused together and forming an open angle; (iv) normally without a pygostyle; (v) with an incisura ischiadica; (vi) rhamphotheca compound; (vii) without apteria or bare spaces in the plumage; (viii) with a complete copulatory organ, moved by skeletal muscles.
Vast majority of snakes are further characterized by having the right and left halves of the under-jaws connected by an elastic band; a median, longitudinal furrow in the skin below and behind the chin; the whole palatal apparatus is but loosely connected with the skull, nowhere articulating with it.
The os magnum of the second row articulating mainly with the lunar of the first, or with the cuneiform, but not with the scaphoid.
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