6o6 



MUSCULAR SYSTEM 



Mammalian equivalent is the m. supraspinatus. In Eatitse it arises 

 almost wholly from the coracoid, and scarcely from the sternum : 

 in Carinatw the lateral margin of its sternal origin is marked by a 

 ridge beginning near the coracoid and running parallel to the keel, 

 or converging towards or diverging posteriorly from the latter. 

 The direction and extent of this ridge afford some taxonomic help, 

 as shewn thus : 



M. propatagialis longus, always present, composed of slips from 

 the mm. deltoides, pectoralis, biceps and cucullaris. Its strong belly 

 originates near the shoulder- joint from the clavicle, scapula and 

 coracoid. Its tendon runs directly to the carpus, forming the 

 outer margin of the patagium or fold of skin between the anterior 

 surfaces of the upper and forearm, which it with the m. propatag. 

 brevis serves to extend, and consists of yellow elastic and blue 

 non-elastic fibres, the latter radiating into and being attached to 

 various portions of the patagium. When the wing is extended 

 the elastic portion is stretched to about three times its ordinary 

 length, to which it returns when the wing is folded. 



M. propatagialis brevis, composed like the last, absent only in 

 Apteryx, Casuarius, Dromseus and the Spheniscidse. In other Birds 

 it is often very complicated the simplest condition being in the 

 Pici, where it consists of a belly and a strong tendon, running 

 down the anterior and outer side of the upper arm, and attached 

 to the proximal tendon of the m. extensor metacarpi radialis longus, 

 a little below the outer condyle of the humerus. In Cuculus its 

 tendon is attached simply to the ulnar fascia, below the elbow- 

 joint. In most other Birds the tendon is split into several portions, 

 and is further complicated by receiving slips from, and by connexion 



