322 THE VERTEBRATE SKELETON. 



The scapula forms a long curved flattened bone expanded 

 at its anterior end, where it meets the coracoid, and lying 

 across the ribs at its tapering posterior end. It helps to form 

 the imperfect glenoid cavity, with which the humerus arti- 

 culates. The coracoid, a shorter but stouter bone than the 

 scapula, has its upper end or head thickened and bears on its 

 posterior border an irregular surface, with part of which the 

 scapula articulates, while the rest forms part of the glenoid 

 cavity. The inner border of the coracoid adjoining the arti- 

 cular facet for the scapula is produced into a strong process 

 which helps to complete the foramen triosseum, a space 

 lying between the adjoining ends of the scapula and coracoid, 

 through which the tendon of the second pectoral muscle passes. 

 The lower part of the coracoid, which is much flattened and 

 expanded, and abruptly truncated posteriorly, articulates 

 with the coracoid groove of the sternum. The clavicle is a 

 thickened curved membrane bone, which is fused with its 

 fellow in the middle line below, the two forming the furcula 

 or merrythought. Its dorsal end is drawn out into a process 

 which articulates with the coracoid. 



THE ANTERIOR LIMB OR WING. 



This consists of three parts, a proximal part, the upper arm 

 or brachium, a middle part, the fore- arm or antibrachmm, 

 and a distal part, the maims. When extended for flight the 

 parts lie almost in the same straight line, but when at rest they 

 are folded on one another in the form of a Z, the brachium and 

 manus pointing backwards, and the anti brachium forwards. 

 When extended for flight the surfaces and borders of the wing- 

 correspond in position with those of the primitive vertebrate 

 limb 1 , the pre-axial border being directed forwards and the post- 

 axial backwards, while the dorsal and ventral surfaces look 

 respectively upwards and downwards. But when the wing is 

 at rest, the humerus as it extends backwards becomes slightly 

 rotated, so that its dorsal surface looks more inwards than 

 1 See p. 28. 



