132 MKKISTK VARIATION. 



I'.nd- investigated by himself. He also gives particulars of the 

 individual variations which were found in certain cases. From 

 thi- table tl.- following statement is compiled, shewing the most 

 iin|,'.r!aii! diversities met with and the instances of individual \ a- 

 i-i:iii,,n. In tin- majority of cases the most posterior spinal nerve 

 ,,f the cervical region was the most posterior nerve of the brachial 

 ple\u-. l.ut in a certain number of cases it does not join the plexus 

 ,il : in some other cases the anterior spinal nerve of the dorsal 



on al-o takes |> -u-t in forming the plexus. As the table shews, 

 of these plan* has been likewise met with as an individual 

 \anat i"ii 



Furbringer's table shews 3 as the minimum number of spinal 

 n. TM- found taking p;irt in the formation of the plexus of any bird 



orvus abyssimcus): the same number has been found as a 



ininiinuni by other observers iii other birds (v. FlJBBKINGER, p. 24-2. 



i. Tin- maximum number was (i, found in Charudrtitx and 



-ome specimen- of <'liiiii1>n. The plexus is generally formed by 4 



or .". -phial nT\ S 



In cases where -everal individuals were examined, individual 

 variation was generally found, as in A user, Po<l<ir<jx, /V/'/.s, Geci- 

 nus and Garrvlus ; in these '-uses the number of spinal nerves 

 whieh took part in forming the bra.-hial plexus varied between 4 

 and "), while in Cnlu ,,/lm, the number even varied between 4 and (i. 



Variations also ,,,-eiirred in this iv-pe.-t between the t wo sides 

 ,,!' tl,.- b.nlv. 1'or example, in a specimen of Aimer cineim* the 

 plexu^ wa- termed on the ri^ht side by the nerves XVI, XVII, 

 \ V I 1 1 and XIX while mi the left side it received a strand from 

 the X Xth nerve iii addition to these. 



A- has been Mated, the lu.st cervical nerve i- -vnerally the last 

 Derve -uppl\in;4 the brachial jilexns but deviations from this plan 

 occur in both directions. These deviations may occur as individual 

 \ar;at i.m> and they may even be unilateral. .w in^ to the ti'ausit ion 

 between the cervical and dorsal vertebra' being effected al different 



point- o|i t he tVVo >ideS of t lie body. 



Particular- ar< given respecting the average proportions of the 



several root- in the different arrangement^, but the arrangement 

 Or -i/'- of the roots r.-latively to each ..ther was not found to bear 

 anv constant relation either to the sv-tematic position of the bird, 



* 



or to it- -i/.e. or to it- capacity for flight. It was however generally 

 found that there was a certain relation between the relative si/e of 

 the root- an. I the length of the neck in birds with a plexus Coiu- 

 p..~ed o| IMIH- roots. In this case the greatest thickness was gener- 

 ally either in or anterior to the middle roots of the plexus in short- 

 n.-cked bird-, but posterior to the middle .,f the plexus in long- 

 necked bird-, but even this rule was imt at all closely observed and 

 many except ion- occurred. Fi i; r,i;i M; 1:1;, /. <. p. 24-S. 



In \ariation in the ordinal positions (l f the spinal nerves com- 

 pM-ing the plexu-. tin- pattern of the plexus as newly constituted 



