

the Lumbo-Sacral Plexus of Macacus rhesus. 245 



not agree wholly with either of the types figured by Sherrington is 

 evident ; but further comparison of the descriptions of the two ob- 

 servers is rendered useless by the fact that Forgue omits to mention 

 the class of monkey he made his observations on. 



Like Sherrington, I confined myself to Macacus rhesus in my experi- 

 ments on the lumbo-sacral plexus, and from numerous careful dis- 

 sections, I am compelled to conclude that, at any rate in those animals 

 dissected by me, one type occurred sufficiently frequently to make it 

 necessary to look upon it as the chief one. But at the same time, 

 among the different variations, one was conspicuously more frequent 

 than any of the others, but scarcely sufficiently frequent, I think, to 

 warrant my at present describing two main types, in the way that 

 Sherrington has done. 



The arrangement in what has been the most common type in the 

 animals which came under my observation was as follows (see 

 fig. 1) : The external cutaneous received fibres from the 3rd and 4th 

 lumbar roots ; the anterior crural from the 4th and 5th, as did the 

 obturator nerve ; and the 6th received a branch from the 5th lumbar 

 root, before its junction with the 7th lumbar root to form the sciatic, 

 which nerve also received a branch from the 1st sacral root. As far 

 as I have seen, the 2nd sacral nerve root never sends a branch to the 

 sciatic, in this type of plexus. 



The variation which I have spoken of above as being the most 

 common has the following arrangement (see figs. 2 and 3) : The 

 external cutaneous is derived from the 3rd and 4th lumbar roots, as 

 in the chief type ; but the 3rd lumbar sends a branch to the 4th before 

 the latter gives off its branches to the external cutaneous, the anterior 

 crural, and the obturator nerves. The anterior crural then receives a 

 branch from the 4th and another from the 5th lumbar roots, as in the 

 chief type ; but the obturator receives, in addition, a branch from the 

 6th lumbar root. The sciatic receives no branch from the 5th lumbar 

 root, but only from the 6th and 7th lumbar and 1st sacral roots. I 

 have been unable by the most minute dissections, aided by magnify- 

 ing lenses, to trace any nerve fibres from the 2nd sacral root to the 

 sciatic trunk. It will be thus seen that the chief points of difference 

 between this and the most common type of plexus consist firstly in the 

 absence of a branch from the 5th to the 6th lumbar root, and there- 

 fore to the sciatic ; secondly, in the fact that the obturator nerve 

 receives a branch from the 6th lumbar root in addition to those which 

 it receives from the 4th and 5th lumbar ; and, thirdly, in that the 3rd 

 lumbar sends a branch to the 4th before the latter gives off any 

 branches to the nerve trunks derived in part from it. 



In the plexus of which fig. 2 is an example there can be no doubt 

 that the 2nd sacral nerve root does not send a branch to the sciatic 

 trunk, while that from which fig. 3 is taken shows how in some cases 



