THE PECTORAL AND PELVIC GIRDLES 1 37 



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 supra- 

 glenoid foramen is present in the Cotylosauria (Fig. 95), Thero- 

 morpha (Fig. 96 d), probably the Therapsida, in most modern Lacer- 

 tilia (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 bor- 

 der; 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 Dou- 

 thitt. 



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 dorso ventral, 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. Doubt- 

 less 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 emar- 

 ginations 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), Chel- 

 onia (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 extraordi- 

 narily developed in the Plesiosauria (Fig. 102), where they sheathe 



