138 MERISTIC VARIATION. [part i. 



and IXth (instead of Vlllth alone, as seen in five cases out of six). 

 But though in all these respects the nerve-supply of the plexus was 

 in ordinal position posterior to the normal, nevertheless the IVth 

 sent a communication to the Vth (as it does normally) and the 

 suprascapular and subscapular were given off normally. Here, then, 

 the supply to the plexus began at the normal place, though it ex- 

 tended further back than it normally does. On the right 'side the 

 branch from the Xth was slightly bigger than usual, but otherwise 

 the only abnormality noted was that the IXth sent a branch to the 

 musculo-spiral. Herrixgham, W. P., Proc. Boy. Soc, 1886, xli. 

 p. 435. In view of Furbrixger's evidence (see Nos. 65 and 67), 

 it might be expected that the first rib would be reduced in corre- 

 lation with the irregular forward Homceosis of the nerves. In 

 reply however to a question on the subject, Dr Herringham has 

 kindlv informed me that no abnormality in the ribs was seen, but 

 that this point was not specially considered. 



Compare also Laxe's case, No. 24, in wdiich similarly a large 

 branch from the Xth joined the plexus on the right side and the 

 first rib was rudimentary, both structures thus shewing a correla- 

 ted forward Homoeosis. 



Lumbo-sacral Plexus. 



'70. By physiological methods Sherrixgtox found that the supply 

 to the lumbo-sacral plexus varied considerably with regard to its 

 origin from the spinal nerves. This w r as seen in Macacus, in the 

 Cat and in the Frog. In none of these animals was any one ar- 

 rangement found sufficiently often to justify its selection as a "nor- 

 mal " type. In each case it was found convenient to divide the 

 different forms of arrangement into two classes, the one in which 

 the supply to the plexus was in ordinal position more anterior 

 (" pre-axial," Sherrington), the other being more posterior (" post- 

 axial," Sherrington). Particulars respecting the distribution of the 

 several nerves and the movements resulting from their stimulation 

 in the two classes, are given in detail (q. v.). In Macacus, 31 in- 

 dividuals belonged to the more anterior class, and 21 to the more 

 posterior. In the Cat the number of individuals in the two classes 

 was 22 and 39 respectively. It is stated generally that 



" The distribution of the peripheral nerve-trunks is not obviously 

 different, whether, by its root-formation the plexus belong to the 

 pre-axial class, or to the post-axial. The peripheral nerve-trunks are, 

 as regards their muscles, relatively stable in comparison with the spinal 

 roots. When the innervation of the limb-muscles is of the pre-axial 

 class, so also is that of the anus, vagina and bladder ; and conversely." 

 Sherrington, C. S., Proc. Roy. Soc, 1892, li. pp. 70 — 76. 



71. Primates. Since in examining the facts of Variation we are 

 seeking for evidence as to the modes in w r hich specific differences 



