WINGS OF BIRDS. 17 



humerus, and immediately jforms a very slender tendon which passes along the 

 humerus to the radius. 



About the middle of the fold, at h, is a dense mass of cellular tissue, to which 

 is attached a thin flap from the deltoid muscle, seen in the figures at h. 



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

 from the lower part of the deltoid near its insertion, attached to the cellular 

 mass at h, and sending off from its lower edge, a very slender tendon, inserted 

 along with that of the tensor plicse. This muscle may be named the retractor 

 plica. 



3. Muscles inserted into the cubitus : — 



The muscles which move the fore-arm on the arm are two, a flexor and an 

 extensor. 



13. Flexor cubiti, or biceps flexor, arises tendinous from the upper extremity 

 of the coracoid bone, passes, 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 ten- 

 don, into the radius, and by a more slender slip into the ulna, between the 

 supinator radii longus, and the 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 origin from the lower ridge of that 

 bone, and from the greater part of its posterior edge, or linea aspera, and is 

 inserted by two tendons into the olecranon, or upper extremity of the ulna. Its 

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



4. Muscles inserted into the hand: — 



As these muscles are numerous, it may be expedient to describe them in the 

 order in which they are seen in the two views. 



In Fig. 2, representing the lower surface of the wing, are observed the follow- 

 ing muscles : — 



15. Extensor metacarpi radialis longior, or supinator radii longus, the muscle 

 seen on the fore edge of the cubitus, arises from the outer condyle of the hume- 

 rus, runs along the anterior edge of the fore-arm, and terminates in a slender 

 tendon, which is inserted into the protuberance on the head of the radial meta- 

 carpal bone, anterior to the first digit. Its action is to bend the arm, and extend 

 the hand, or bring it into a straight line with the cubitus. The insertion of the 

 biceps cubiti, 13, is between the head of this muscle and that of the pronator 

 teres, 21. 



16. Of the muscles that arise from the inner condyle, the first or most external 

 is the flexor carpi ulnaris, which comes off by a tendon from the lowest part of 

 the condyle, passes along the inner and posterior side of the ulna, in contact with 



No. 7, Vol. II. c 



