38 INTRODUCTION. 



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 humerus, and 

 immediately forms a very slender tendon, which passes along 

 the humerus to the radius. 



About the middle of the fold, at 7^, is a dense mass of cellular 

 and elastic tissue, to which is attached a thin flap from the 

 deltoid muscle, seen in Figs. 2 and 3 of Plate III, at h. 



12. Besides which, there is a thin muscle arising from an 

 aponeurotic base, from the lower part of the deltoid near its in- 

 sertion, attached to the cellular mass, and sending off from its 

 lower edge a very slender tendon, inserted along with that of 

 the tensor plicae. This muscle, which does not appear to have 

 been previously observed, may be named the retractor plicce. 

 I have not met with it in any other birds than Pigeons. In 

 the Thrushes its place seems to be supplied by an enlargement 

 of the slender muscle of which the tendon is seen between 11 

 and 13, in Fig. 3, and which in them is inserted into the ulna. 



III. Muscles inserted into the cubitus. 

 The muscles which move the fore-arm on the arm are two, 

 a flexor and an extensor. 



13. Flexor cubit I, or biceps flexor^ arises tendinous from the 

 upper extremity of the coracoid bone, passing, flat, under the 

 insertion of the pectoralis major, and also from the flat surface 

 and edge of the inferior crest of the humerus, runs along the 

 anterior and inferior face of that bone, and is inserted by a short 

 tendon into the radius, and by a more slender slip into the 

 ulna, between the supinator radii longus, and pronator radii 

 teres. Its action is to bend the cubitus on the humerus. 



14. Extensor cubiti arises from the anterior extremity of the 

 scapula, from the head of the humerus, by another distinct ori- 

 gin from the lower ridge of that bone, and from the greater part 

 of its posterior edge or linea aspera, and is inserted by two ten- 

 dons into the olecranon or upper extremity of the ulna. Its 

 action is to extend the cubitus, and raise it a little. 



lY. Muscles inserted into the hand. 



