122 MORPHOLOGICAL TYPES 



After this come six free caudal vertebrae, and then four 

 more all fused up together to make the pygostyle. 



Pectoral Girdle and Limb. — The shoulder girdle is formed 

 of scapula and coracoid (cartilage-bones), and a clavicle 

 (membrane-bone) which meets its fellow from the other side 

 in the middle line to form the furcula, or " merrythought.'* 

 The scapula extends backwards over the ribs ; the coracoid 

 is attached to the sternum. Where the scapula, coracoid, and 

 clavicle meet, they enclose a foramen (triosseum) between them, 

 which acts as a pulley through which the tendon of the minor 

 pectoral muscle passes, to be inserted on the humerus and so 

 raise the wing. 



The sternum is remarkable for its relatively enormous 

 median keel or carina. On each side of it the pectoral muscles 

 are inserted. Of these, the minor pectoral muscles have been 

 mentioned above ; the major pectoral muscles pull the wing 

 down and in so doing lift the bird in the air. The difference 

 between " red meat " and " white meat " can be well shown 

 in the pectoral muscles of different birds. Muscles which 

 perform long-continued actions are rich in sarcoplasm and 

 haemoglobin, and are therefore red. Other muscles, the action 

 of which is not continuous, are poor in sarcoplasm, and their 

 fibres are therefore white in colour. The falcon is a bird 

 which spends long periods on the wing, during which its 

 pectoral muscles are in continuous activity. It is not sur- 

 prising to find therefore that these muscles are " red meat." 

 On the other hand, the domestic fowl does not use its pectoral 

 muscles continuously, and they are white. 



The skeleton of the wing consists of humerus, radius, and 

 ulna. The wrist and hand are somewhat modified ; there are 

 two free proximal carpal bones, the radiale and ulnare ; but 

 the distal carpals have fused with the three fused metacarpals 

 to form a carpo-metacarpus. The first digit is represented by 

 a phalanx bearing feathers which form the " bastard wing." 

 The remaining two digits have two and one phalanges respec- 

 tively, and they, together with the carpo-metacarpus, bear 

 the primary remiges. 



Pelvic Girdle and Limb. — The pelvic girdle is at first sight 



