298 St. J. Brooks, 



should be reached by the ultimate twigs of the nerve which has been 

 cut, — if the accounts given in anatomical text books are correct. 

 A striking example of this is shown in Fig. 6 *), where the fourth and 

 fifth fingers are seen to be considerably affected by section of the 

 musculo -spiral nerve. 



Having incidentally observed, in the course of my usual work in 

 the dissecting room, that the twigs of the radial and ulnar nerves 

 occasionally crossed one another, or overlapped in their distribution, 

 on the dorsum of the hand, it occurred to me that the phenomena 

 observed after section of nerves might be explained by something more 

 than mere anastomoses, — that it was possible that a given area of 

 skin might be very commonly supplied by twigs from two different 

 nerves : I was at that time unaware that R. Jacobi 2 ) had already ad- 

 vocated a similar theory m regard to the „collateral innervation of 

 the skin". As I believed that by means of special dissection it would 

 be possible to trace the nerves nearly to their terminations, I pro- 

 ceeded as follows ; — after securing the trunks of the palmar digital 

 branches of the median and ulnar nerves and also the radial, the dorsal 

 branch of the ulnar and the external cutaneous branch of the musculo- 

 spiral, I proceeded to remove the skin / superficial and deep fascia, 

 with the nerves included, from the back of the hand and from the 

 fingers. A longitudinal incision was made along the centre of each 

 finger on its volar aspect, the skin reflected towards the dorsum, and 

 the nails, with as much of their matrix as possible, were also retained 

 in connection with the skin. The skin was then pinned down, with 

 the deep surface upwards, in a cork-lined tray and the nerves followed 

 out under water. The first hand that I examined in this way was 

 somewhat disappointing, inasmuch as the amount of crossing of the 

 nerves was inconspicuous. The second example, however, showed con- 

 siderable intercrossing of the radial and ulnar nerves and I therefore 

 determined to make every effort to ascertain the ultimate distribution 

 of their twigs. The dissection occupied about twenty-six hours and 



*) Op. cit. p. 105. This figure has been reproduced in the accompanying plate; 

 see fig. 5. 



2 ) „Ein merkwürdiges Sensibilitätsphänomen". Von Dr. Rud. Jacobi. Berliner 

 klin. Wochenschrift, 6. und 20. Juni 1887. 



