16 . WINGS OF BIRDS. 



6. The pectoralis minor is a small muscle which arises from the lower two- 

 thirds of the outer edge of the coracoid bone and the anterior margin of the 

 sternum, under the articulation of the ribs, forms a small round tendon, which 

 passes outwards and forwards, and is inserted into a prominent internal 

 tubercle of the humerus, which it pulls downwards and backwards. 



7. Above and before the pectoralis minor is a small muscle, arising from the 

 upper part of the coracoid bone, and a strong fascia extended from its base to 

 its extremity above, passing obliquely upwards, and being inserted anteriorly 

 to the pectoralis minor: Its action is to draw the humerus directly 

 downwards. 



The muscles which arise from the scapula to be inserted into the humerus 

 are the following : — 



8. The supra spinatus, Fig. 1, arises from the fore part of the scapula, and 

 is inserted into the posterior or inner crest of the humerus, externally of the 

 tendon of the pectoralis minor. 



9: The infra spinatus arises from the outer surface of the scapula, as far a 

 its extremity, and is inserted into the same prominence as the last. These two 

 muscles draw the humerus backward. 



The subscapularis arises from the fore part of the inner or under surface 

 of the scapula, and is inserted into the same protuberance. 



10. The deltoides arises from the fore part of the scapula, and from the top of the 

 coracoid bone, its anterior fibres being in contact with those of the pectoralis major. 

 Its anterior portion is inserted into the outer and back part of the edge of the 

 anterior crest of the humerus, its posterior into that bone, as far as the origin of 

 the supinator radii longus, that is, four-fifths of its length. A thin flap is at- 

 tached to the skin in the bend of the wing. The deltoid muscle raises the 

 humerus. 



Under the deltoid is the coraco-brackialis, which arises from the tip of the 

 coracoid bone, and adjoinipng part of the scapula, and is inserted into the prox- 

 imal part of the crest of the humerus. Its action is to pull the humerus forward 

 and upward. 



The muscles inserted into the cubitus or fore-arm, come next in order ; but it 

 may be proper here to describe a very curious apparatus existing in the bend of 

 the wing anteriorly, between the shoulder and wrist joints, b and d. ' At that 

 part, the edge of the wing is formed by a fold of the skin enclosing an elastic 

 substance, and edged with an elastic tendon or fibre, which has at its commence- 

 ment at the shoulder-joint a small muscle detached from the pectoralis major. 



11. This muscle, named the tensor plicae, alee, or stretcher of the fold of the 

 wing, has its terminal insertion in the prominence at the base of the metacarpal 

 bone at d. Another smaller slip comes off" behind from the anterior ridge of the 



