Further, it is considered that too much weight has been assigned to the characters distinguishing monotremes from other mammals, foetal marsupials showing a monotreme type of coracoid, while it is probable that in the long run it will be found impossible to maintain the essential dissimilarity between the milk-glands of monotremes and other mammals.
- Scapula, coracoid and clavicle, meet to form the foramen triosseum, through which passes the tendon of the supracoracoideus, or subclavius muscle to the tuberculum superius of the humerus.
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.
Coracoid and scapula fused.
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.
The coracoid is a prominent rounded nodule.
The element often termed "coracoid" in these fossils would be the scapula.
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.
In these batrachians the pectoral arch falls into two distinct types - the arciferous, in which the precoracoid (+clavicle) and coracoid are widely separated from each other distally and connected by an arched cartilage (the epicoracoid), the right usually overlapping the left; and the firmi- sternal, in which both precoracoid and coracoid nearly abut on the median line, and are only narrowly separated by the more or less fused epicoracoids.