glenoid fossa and opening on the inner side at the lower end of the subscapular fossa; the glenoid foramen, entering the glenoid fossa and opening on the inner side in front of the subscapular fossa; and the supraglenoid foramen entering the supraglenoid fossa near the hind border and opening at the upper end of the subscapular fossa. The glenoid foramen has not been observed in reptiles. The supraglenoid foramen is present in the Cotylosauria (Fig. 95), Theromorpha (Fig. 96 d), probably the Therapsida, in most modern Lacertilia (Fig. 99), and in Sphenodon. It will probably be found in many other forms when searched for. Its external orifice, however, varies much, even in the Theromorpha. In Ophiacodon only, so far as has been observed, does it enter the supraglenoid fossa back of the border; more usually, as in many modern reptiles, it is on the outer face of the scapula in front of the border, at a variable distance above the glenoid surface. A small artery traverses it, according to Douthitt.
In the early cotylosaurs and theromorphs (Fig. 106) the glenoid articulation is more or less spiral or "screw-shaped." In most other reptiles it is a simple, oval cavity. In the pterosaurs (Fig. 109) it is saddle-shaped, concave in the dorsoventral, convex in the conjugate, diameter, permitting motion of the arm in two planes only, dorso-ventral and antero-posterior.
The double coracoids are never elongated transversely. Turned inward at nearly a right angle from the plane of the scapula, they were approximated along their mesial borders (Fig. 96 d), as shown by many specimens in which they have been found in place. Doubtless epicoracoid cartilages occupied the interval in front.
In the single coracoid of later reptiles the glenoid articulation has been completed from behind. In the modern lizards there are emarginations of the mesial border (Fig. 99), the deeper one opposite the supracoracoid foramen; this emargination is very variable in the mosasaurs. It has also been observed in the procoracoid of the theromorphs. The coracoid of the Pterosauria (Fig. 109 a), Chelonia (Fig. 109 b), and Crocodilia (Fig. 112) is elongate. When the sternum is present the coracoid articulates with its anterior lateral border.
The coracoids, presumably the precoracoids only, are extraordinarily developed in the Plesiosauria (Fig. 102), where they sheathe
