408 JAMES CRAWFORD WATT 



6. Flexor Digitorum Profundus (detached portion) (fig. 8, F. D. P.) 



Origin. From the neck of the radius and the shaft of the 

 bone near this on the medial (apparently ventral) border. 



Insertion. This muscle is long and slender. As it is followed 

 distally into its tendons it divides into a superficial and deep 

 layer which insert separately. The superficial tendon passes 

 down to the lower end of the radius and to the carpus. The 

 short deeper tendon ends almost immediately on the shaft of 

 the radius a short distance above the lower extremity, and is 

 fused with the short deeper tendon of the extensor carpi ulnaris 

 already described. 



This muscle I interpret as the ulnar part of the flexor digi- 

 torum profundus, which has differentiated during the muscle 

 development of the limb and become attached to the nearest 

 part of the radius. The flexor digitorum sublimis by the exten- 

 sion of its deep, radial origin, comes between it and the radial 

 portion of the profundus layer and so may have prevented their 

 fusion. On the contrary if the lack of fusion was primary 

 this would allow of the sublimis layer becoming attached down 

 the radius between the two parts of the profundus. There 

 is no possibility of this being the flexor pollicis longus as it lies 

 medial and not lateral to the rest of the flexor digitorum 

 profundus. 



Fourth layer 



7. Pronator quadraius 



A thin film of transversely disposed muscle fibers lying over 

 the lower end of the radius represents the pronator quadratus 

 muscle. It is very poorly developed and small in extent. 



It is to be noted that by means of the muscle in the forearm volun- 

 tary flexion of the digit is possible but voluntary and active exten- 

 sion is impossible, as all extensors fail to reach the finger. A singu- 

 lar and interesting parallel to this case is found in a case cited by 

 Schultze ('04). In a training school he observed a nineteen 

 year old lad who had only one digit on each of all four limbs. 

 Voluntary flexion of these digits was easily accomplished but he 



