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.
In most of the Caudata the scapular region alone ossifies, but in the Ecaudata the coracoid is bony and a clavicle is frequently developed over the praecoracoid car tilage.
The coracoid is one of the most characteristic bones of the bird's skeleton.
From the inner side of the neck of the coracoid arises the precoracoidal process, the remnant of the precoracoid.
Its strong belly originates near the shoulder joint from clavicle, coracoid and scapula.
The coracoid is a prominent rounded nodule.