215 



and Physiology, 1894, p. 84 and 169) reported the XXIV spinal nerve 

 as furcal 19 times in 23; the XXV as furcal 4 times (17,4 7o)- 



In the 246 plexuses here tabulated the part of "furcal nerve" 

 was played by the XXIV and XXV spinal nerves in 15 instances 

 (6,1 7o) ^iid by the XXV spinal nerve alone in 23 instances (9,7 7o)- 

 EisLER therefore found two furcal nerves, the XXIV and XXV, in a 

 greater proportion of instances than we observed, but the XXV nerve 

 as sole furcal nerve much less frequently. The proportional number 

 of instances in which the XXV spinal nerve contributed to the anterior 

 nerves is approximately the same in Eisler's tables and in ours. 

 The unusual furcal nerves were found by the British Committee of 

 Collective Investigation considerably less frequently than either by 

 EiSLER or by us. 



The Nat iral and Artificial Separation of the Sciatic 

 Nerve into its constituent Branches, the Peroneal and 



Tibial Nerves. 



During early embryonic development and in a certain proportion 

 of instances in the adult, the peroneal and tibial nerves are separate 

 from their origin from the spinal nerves that enter into the formation 

 of the sacral plexus. As has been pointed out above, the territories 

 supplied by these two nerves are well marked and distinct. It is 

 therefore important in a study of lumbo-sacral plexus to separate the 

 sciatic nerve into its constituent branches back into the sacral plexus. 

 In an artificial separation of this kind it is of course possible that 

 minute bundles of nerve fibres may be broken. But the essential gross 

 relations of the peroneal nerve may be determined, at least, in this 

 way and in no other. During the earlier years of our investigation 

 we did not, as a rule, artificially separate the tibial and peroneal 

 nerves. The statistics as to the distal limit of origin of the peroneal 

 nerve have therefore in most instances to be based upon our records 

 of the past two years as is indicated in the tables. 



A natural separation of the peroneal and tibial nerves is found 

 when during embryonic growth the piriformis muscle has developed 

 in whole or in part between the two nerves, which, as has been said, 

 are during early development distinct. Such a natural separation of 

 the nerves in the adult was found in 26 instances in the 246 plexuses 

 charted, about 10 %• As will be seen by glancing over the tables 2 

 to 8 the distribution of these plexuses showing natural separation of 

 the tibial and peroneal nerves is a very even one, occurring in about 

 10 7o of instances in each type of plexus. Eisler found this condition 



