76 THE MYOLOGY OF THE EAVEN. 



tendinous, and finally form a stroncr, somewhat flattened 

 tendon, which is inserted into the ulnar crest of the 

 humerus, on the proximal margin of the pneumatic 

 fossa, at about its middle point. 



This muscle assists the pectoralis secundus in elevating 

 the humerus, when it is brought into action by the 

 contraction of its fibres. 



Professor Owen seems to have found quite a different 

 origin and insertion in other birds for this muscle, as he 

 says, " the third pectoral muscle, which is in general 

 the smallest of the three, arises from the anterior part of 

 the sternum at the angle between the body and the keel, 

 and also by a more extended origin, from the posterior 

 moiety of the inferior surface of the coracoid and the 

 coraco-clavicular membrane ; it is directed forward, 

 rising to pass through the scapulo-coracoid trochlea ; 

 its tendon glides through a sheath, attached to the 

 capsule of the shoulder-joint, and in some birds to the 

 OS humero-scapulare ; and is inserted into the radial 

 tuberosity of the humerus, which it helps to raise. It 

 is proportionally large in the Penguins and Gulls, but 

 attains its greatest development in the Gallinaceous 

 order" {loc. cif., p. 97). 



Mr. Forbes, who investigated the myology of the 

 Tubinares, collected during the voyage of the Chal- 

 lenger, found the ^^ecfora/^s tcrtius in them to be " in 

 the form of a broad, thin band, more or less parallel 

 with the coracoid, occupying the superior half of the 

 broad space between that bone and the furcula, its fibres 

 arising chiefly from tlie strong membrane between these 

 bones, sometimes with additions from the anterior mar- 

 gin of the coracoid, or from the body of the sternum 

 close to the middle line " [Coll. Memoirs, p. 390). 



Before closing my account of this group of muscles, I 



