214 



The Furcal Nerve. 



In 1878 Jhering ^) called definite attention to the "furcal nerve" 

 a spinal nerve which sends fibres both to the anterior and to the 

 posterior nerves of the limb. 



In man, Jhering applied this term to the fourth lumbar nerve. 

 He erred, however, in supposing that the XXIV spinal nerve occupies 

 this position more constantly than it does. Eisler performed good 

 service in pointing out clearly the great variation that occurs in the 

 "furcal" nerve. Eisler, in his article on the lumbo-sacral plexus, 

 considers it almost wholly from the point of view of the "furcal" 

 nerve. The most anterior form of plexus which he mentions is one 

 in which the XXIII, besides supplying the obturator and femoral nerves, 

 sends a small bundle of fibres to the sacral plexus and the XXIV 

 sends fibres to both the lumbar and sacral plexuses. Here we have 

 two furcal nerves, the 23. and the 24. He found no plexus in which 

 the 23. was the sole furcal nerve. The next more distal type of 

 plexus is that in which the XXIV nerve sends the greater bulk of 

 its fibres to the sacral plexus, then comes one in which the XXIV 

 nerve sends the main bulk of its fibres to the obturator and femoral 

 nerves. Eisler divides plexuses of the latter type into two groups. 

 Then follows a type of plexus in which the XXIV and XXV nerves 

 both are furcal nerves and lastly one in which the XXV spinal nerve 

 alone plays the part of a furcal nerve. 



In three out of 127 plexuses he found the third lumbar nerve 

 sending a small bundle of fibres into the communicating branch to 

 the great sciatic nerve. We have found a similar small twig in 6 

 out of 246 plexuses (see tables A and B). In several of these, however, 

 the bundle of fibres from the XIXIII spinal nerve was exceedingly 

 delicate so that it was impossible to follow it into the great sciatic 

 nerve. 



Eisler found the fourth and fifth lumbar nerves giving fibres to 

 nerves of both the lumbar and sacral plexuses in 16 out of 127 in- 

 stances (12,6 7o)- 111 three instances the fifth lumbar nerve alone 

 acted the part of a furcal nerve (2,4 7o)- The Committee for Collective 

 Investigation of Great Britain and Ireland, reported (Journal of Anatomy, 

 Vol. 29, 1885) that in 110 plexuses the position of the furcal nerve 

 was occupied by the third lumbar nerve in one instance and by the 

 fifth lumbar in 6 instances (5,4 7o)- Paterson (Journal of Anatomy 



1) Centralbl. f. d. med. Wissensch., No. 9. 



