ANATOMY OF A MONODACTYLOUS FOETUS 399 



presents a free crescentic border under which are visible the other 

 tendon of the biceps and the tendon of the brachiahs muscle. 

 There is some fusion of the deep fascia of the arm to the muscle 

 at the beginning of this superficial tendon, which might be 

 interpreted as a rudimentary semilunar fascia. 



The attachment to the humerus must be extremely rare as it 

 has not been noted by such an authority as Le Double and no 

 explanation of such an attachment can be drawn from compara- 

 tive anatomy. The only plausible theory to be entertained is 

 that this is possibly an extremely well developed semilunar 

 fascia which has obtained a bony attachment by following the 

 intermuscular septa to the bones. , 



The median nerve passes on the superficial surface of this 

 broad tendon while the brachial artery and vein pass deep to it, 

 and also behind the round tendon. 



The biceps muscle is responsible for the position of partial 

 supination of the radius, though the hand is pronated. It is 

 to be remembered that one action of the biceps normally is 

 rotation of the radius to produce supination, accomplishing this 

 by a forward pull on the bicipital tubercle which lies posterior 

 to the long axis of the bone in pronation. In this case the radius 

 has been rotated until the bicipital tubercle lies facing the ante- 

 rior surface of the humerus. There are no muscles attached 

 to the radius capable of opposing the biceps in this action and 

 so the position of supination will be permanently retained. 



THE BRACHIALIS MUSCLE 



This muscle is divided longitudinally into two portions. 



Medial portion (fig. 8, Br.) 



Origin. Normal in extent from the lower half of the front 

 of the shaft of the humerus. 



Insertion. The muscle passes down on the humerus almost 

 to the articulation with tlie radius. It is inserted along a 

 continuous line on the back of the neck and head of the radius, 

 the joint capsule and the medial epicondyle of the humerus dis- 



