I I I MERI8TII VARIATION. [PART i. 



\ I,--., n 1 //'/' < ,<*<ynj nerves in tit? fore-limb, the following principles 

 \\en- -imilarh ' !-h-d l.y di>-'-'-t i'.n in Man. 



1. -i.i two -p..t- on the skin, that which is nearer the prc-axial 

 ii..i-diT ii-niU t" \- -upplied I iy tin- higher nerve. 



i'. --(if two -pots in tin- pre-axial area the lower tends to be 

 -upplie.1 liv tin- lower nerve, and of two spots in the post-axial area the 

 lower t.-ii-l- t., 1,.- supplied by tin- higher nerve." 



"Tim-, if the liml' !> seen from tin- front, the two highest nerves 

 on the outer ami iniifi- >ide- re-peetively are the IVth and Xth. 

 I. .-i than the-,- tli- Vth and Vlth take the outer, the IXtli and 

 Xtli the inner .-id.-. llelow tin- elbow the Vlth alone takes the outer, 

 and tli.- [Xth alone the inner. In the hand, while tin- Vlthand IXth 

 continue their po-itions, the V I Ith and VTIIth for the first time join 

 in the supply." 1'a i titulars from which this general statement is made 

 are given. II UMIIM.H \M, I.e. p. 43!>. 



A.-eeinliiiL,' to -uli-ei|iient investigations of SHERRINGTON's on the 

 l,'iiiil-liii<l>. the iiinei-\atioii of the muscles of the posterior aspect of the 

 thL'h and \<-^ do riot follow the third of Herringham's principles, for in 

 their case tli.- deep lay.-i- of muscles is innervated by roots anterior to 

 tin.-,- w 1 1 i.-li innervate the -uperiieial muscles. The same experiments also, 

 though eleai-ly -hewing th:it the nerve-supply of the skin of the hallux 

 i- anterior bo that of th.- ."nh digit, gave only equivocal evidence that 

 the -am.- \\as true of tin- mii-eul.-it ures of these two digits; and in the 

 thiudi the gra.-ilis is not supplied before the vastus externus, whose 

 relation i- iMther that ..f \.-ntral to dorsal than of anterior to posterior-. 

 SHEBBINGTON, C. >.. Proc. /.'"//.>'"'., 1^'Ji', LI. p. 77. 



RECAPITULATION. 



S.iin.- r.-a t ures in the Meristie X'ai'iat ion of the spinal nerves, 

 as illu.-trateil by tin- foregoing .-vuleuee. may be briefly sum- 

 marized 



In tin- tii-st place, as inio-ht be anticipated from the compound 

 natui-.- of a pinal Derve, when lloiiiieotie Variation takes place, it 

 <le not commonly occur by the fcransformatioD of I'ntire nerves, 

 but rather by change in the distribution and functions of parts of 

 ner\.-. In tin- respect, thereloiv, th.-iv is a dit't'ercnce between 

 lloimrosis iii spinal oerves and that in \ertcbrie, for in the latter, 



I b illl'eoMS i> ,,1'lcn complete. 



A roiiLfli illustrai ion may make this more clear. 



In-! as in making up the chapters of a book into volumes, 

 \\hoh- chapter.-, ma\ be put into one \olmne or into the next, and 

 the following chapters renumbered, so it IIKIV be with the Varia- 



ti f vertebrffij for these may belong \\liolly to one region of the 



-pun- or i" another. Hut tin- oerves an- like chapters made up of 

 sections : |>ariicnlar sections or groups <>f sections mav come in an 

 earlier chapter ,,r in a Mibse([iieiit one, and the places of those that 



li:i\e been |||o\e.| OH l|!;i \ be tilled tl| I Col I Sec 11 1 j \ , 'ly, bllt it SeUlolll 



happens that \\hol.- chaptei-s ;i r.- renumbered. Nevertheless it is 

 l.-ar from -uch a case as that <>f /)'/v/(///^//.s- and Cltulu'pus, on the 



