1 64 THE SUPERIOR EXTREMITY 



phalangeal joints, forms, in each finger, an osteo-fibrous 

 canal, in which are enclosed the tendons of the flexor 

 digitorum sublimis and the flexor digitorum profundus 

 together with their surrounding mucous sheath. 



Leave the fibrous sheath of the middle finger intact 

 for revision, but open the other fibrous sheaths by longi- 

 tudinal incisions. They will be seen to be lined with a 

 mucous sheath which is reflected over the enclosed tendons 

 so as to give each a separate investment. Examine the extent 

 of each mucous sheath with the aid of a blunt probe. The 

 mucous sheath of the little finger has been seen to be a direct 

 prolongation from the common mucous sheath of the flexor 

 tendons ; the other three are distinct from that, but they are 

 carried proximally into the palm. They envelop the tendons 

 of the ring, index and middle fingers, as far as a line drawn 

 across the palm immediately proximal to the heads of the 

 metacarpal bones. 



If the flexor tendons are raised from the phalanges, certain 

 mucous folds will be noticed connecting them to the bones. 

 These are termed the vincula tendinum. Two kinds of 

 them are distinguished, viz., vincula brevia and longa. In the 

 accompanying illustration (Fig. 72) the connections of these 

 may be seen. The vincula brevia are triangular folds 

 which connect the tendons, near their insertions, to the 

 volar aspect of the more proximal phalanx. The vincula 

 longa are not invariably present. They are placed more 

 proximally, and are narrow, weak strands which pass between 

 the tendons and the bones. 



Insertions of the Flexor Tendons. The insertions of the 

 two flexor tendons can now be studied. On the volar side of 

 the first phalanx the tendon of the flexor sublimis becomes 

 flattened and folded round the subjacent cylindrical tendon 

 of the flexor profundus. It then splits into two parts, 

 which pass dorsal to the tendon of the flexor profundus, 

 and allow the latter to proceed onwards between them. 

 Dorsal to the deep tendon the two portions of the tendon 

 of the flexor sublimis fuse together, and then, again, they 

 diverge, to be inserted into the borders of the body of the 

 second phalanx. By this arrangement the flattened tendon 

 of the flexor sublimis forms a ring, or short tubular passage, 

 through which the tendon of the flexor profundus proceeds 

 onwards to the base of the ungual phalanx, into which it is 



