WINGS OF BIRDS. 
17 
humerus, and immediately 7orms a very slender tendon which passes along the 
humerus to the radius. 
About the middle of the fold, at 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 and sending off from its lower edge, a very slender tendon, inserted 
along with that of the tensor plicae. This muscle may be named the retractor 
plicae, 
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 cuhiti^ 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. T, Vol. 11. c 
