136 MKRISTIC VARIATION. [PART i. 



in illustration, concerning the composition of the median and ulnar 

 IM-I jpectively. 



Tli.- ni'i/iiin is formed by two he-ads from the plexus; into the 

 outer h.ad ili- Vlth and Vl'lih spinals enter, while the inner is 

 t..im.-d bv branches of the VHIth and IXth, sometimes with the 

 ailditioii of some bundles of the Vllth. The presence of film - 

 froin ill-' \'llth depends on whether the anterior branch of the 

 VI Ith bifurcates, .r goes wholly to the anterior (outer) cord of the 

 pl.-xu-. In order bo - e whether both Vlllth and IXth contribute 



the median, twenty-eight dissections were made, fourteen in 

 infants, fourteen in adults. In one foetus and in one adult no 

 branch tn-m the JXth was found, these being the only except inns 



the rule that b..th VI lMi and IXth send fibres to the median 

 'I'll.- median i- ill' n made of the Vlth, Vllth, Vlllth and 

 I \th. but the-,- roots <lo not send to it a constant proportion. The 

 bund!.- fr..m ill.- Vlth varit-s little, that from the Vllth varies 

 con-id.Tablv. that i'r..in tin- Vlllth is sometimes equal to, some- 

 times smaller, and -.>in> -i mies larger than the bundle from the IXth. 



Tin- origin of ill.- nliKir n.r\e was traced in thirty-two cases, 

 fourteen being adult-. It \\a< fuiind to arise in four differ, i it \\ays. 

 M..-r .-.1111111. .lily it arose tr<>in tin \'lllth and IXth: this occurred 

 in tuenty-thi. .- cases. With the Vlllth and IXth is sometimes 

 combined a -trand from tin- \'llth, as shewn in five cases (four 

 fn-tal. '.in- adult). In thr.-r t'u-tal cases it arose from th'- \" I 1 1 1 h 

 niilv. and in mi'- fo-tal and one adult case from the Vllth and 

 VI I Ith. The Vllth is only added t<> the idnar in some of those 

 -in \\hi.-h it gives a branch to the posterior (inner) cord of the 

 pi. \n-. In several cases the branch t'n .m the X'lIIth was much 

 larger than thai lr..ni the IXth, but the reverse \vas never met 

 with. 



K\ ill. -nee similar \ the above is ^i\en respect in-' other nerves 

 tr..m the bra.-hial jilexu-. 



Ft. .m the re-idt- of t he in\e>| igat i.n ;_;< in rally, it a]i]ieared that 

 the ran^e of N'anatioii tlnnigh considerable was ii"t extravagant, 

 and that uln-n [.arts, usually sii].]ili.d by sdne given nerve root, 

 an- -ii|.|,li. d by some oth.-r n<\. this otln-r rod i.- then eith. r the 

 one aiiieriitr or the one |>.teri..r \ the rod lidn \\hich the sit]>]>lv 

 Dormally cornea Sum.- muscl. - seemed to bear definite relations 

 to each other and their nerve >u|>|ily seemed also "to \arv solidly," 



their Derve .-u|.|.lie- remaining the same ivlativelv to each other, 

 though d. ii\.d from a different root. "The besl example of this 

 is in the three miis.-les which are attached along the inner side of 

 the bicijiital groove, lh.- siibsca|.ularis, t.-r. - major, and latissimus 

 d.'i'si. The tn-t i- n-iially sU].].li.-d b\ the Vth and Vlth, the 

 Second b\ the \'|th, and the last by the Vllth, and however much 

 th.-y max \ary above and be]..\v their t\pical place they do not 

 change their relations to .a.-h other. A similar relation exists 

 between the t\\.. supinatoi-s and the two radial extensors. r J'he.s.- 



