98 ANATOMY OE VEKTEBRATES. 



the Raptores and many Natatores^ especially tlie Penguins, and 

 attains its greatest relative size in the Masoresj where it arises 

 from almost the whole of the coracoideum. 



Birds in general possess t\NO flexors 31 and one extensor, fig. 35, 

 27, of the fore-arm. They have also muscles corresponding to 

 pronators and supinators, but their action is limited in the feathered 

 tribes to inflexion and extension of the fore-arm, and to adduction 

 and abduction of the hand. 



A remarkable muscle, partly analogous in its origin to the cla- 

 vicular portion of the deltoid, but differently inserted, is the ex- 

 tensor plicce cdaris, ih. 3o, a^, b, and forms one of the most powerful 

 flexors of the cubit. It is divided into two portions, of which the 

 anterior and shorter arises from the internal tuberosity of the 

 humerus ; the posterior and longer from the clavicular extremity 

 of the coracoid bone. In the Ostrich and Rhea, however, both 

 portions arise from the coracoid. The posterior muscle, b, sends 

 down a long and thin tendon which runs parallel with the hu- 

 merus, and is inserted, generally by a bifurcate extremity, into 

 both the radius and ulna. The anterior muscle, a, terminates in 

 a small tendon which runs along the edge of the aponeurotic ex- 

 pansion of the wing. In this situation it becomes elastic; it 

 then resumes its ordinary tendinous structure, passes over the 

 end of the radius, and is inserted into the short confluent meta- 

 carpal, u. It combines with the preceding muscle in bending the 

 fore-arm ; and further, in consequence of the elasticity of its 

 tendon, puckers up the soft part of the fold of the wing. 



A lesser flexor of the fore-arm, and stretcher of the alar mem- 

 brane, ib. 31, arises, as a portion of the serratus magnus from the 

 ribs, and terminates in an aponeurosis inserted into the alar 

 membrane and fascia of the fore-arm ; it is represented in fig. 35 

 as turned aside. 



The extensor metacarpi radialis longus, ib. 32, is the first 

 muscle which detaches itself from the external condyle of the 

 humerus, s, and it forms the radial border of the muscular mass 

 of the fore-arm ; it terminates in a large tendon about the middle 

 of the fore-arm, and this tendon passes along a groove of the 

 radius, over the carpus, to the phalanx of the metacarpal, s, into 

 the radial margin of which it is inserted. It raises the hand, draws 

 it forward toward the radial margin of the fore-arm, and retains 

 it in the same plane. In the Penguin this muscle is extremely 

 feeble, and the tendon is lost in that of the tensor jjlicce alaris. 



The extensor metacarpi radialis brevis, ib. 33, arises below the 

 preceding from the ulnar edge of the radius, and is inserted into 



