No. 4.— Variations in the Brachial and Lumbo-Sacral Plexi of 
Necturus maculosus Rafinesque! By F. ©. WAITE. 
Variations in the position of the pelvic girdle in Vertebrates, espe- 
cially in Amphibia, have already been noticed by several authors ; 
Adolphi, Bourne, Case, Howes, G. H. Parker, and others. These varia- 
tions, which obviously involve an inconstancy in the number of presacral 
vertebra, are as a rule symmetrical, the entire girdle being one segment 
caudad — more rarely cephalad — to the usual position ; but infrequent 
instances are found in which the right and left constituents of the girdle 
have unsymmetrical positions. 
Closely associated with the pelvic girdle is the lumbo-sacral plexus, 
and the problem which suggests itself in this connection is to determine 
whether, with the variations known to occur in the skeletal structures 
of the girdle, there are correlated variations in the Jumbo-sacral plexus. 
If, as some morphologists believe, a difference in the position of the 
sacrum is the result of increase in the number of vertebrae by splitting 
of one or more presacral vertebra, or decrease through fusion, then 
such phenomena must take place in one or the other, or both, of two 
regions, either anterior to the most posterior nerve of the brachial 
plexus, or between that point and the lumbo-sacral plexus. 
To obtain evidence upon these alternatives, 1 dissected out the 
brachial plexus, in addition to the lumbo-sacral, in all the Specimens 
which I have studied, As this plexus involves less variation than does 
the lumbo-sacral, I shall discuss it first. 
In naming the spinal nerves, I have adopted the plan of calling that 
nerve which emerges between the cranium and first vertebra the first 
nerve,” succeeding nerves being consecutively numbered. 
So far as I have noticed, there is little variation among either the 
sympathetic or dorsal branches of the spinal nerves. Since only the 
ventral branches enter the plexi, I shall, for the sake of brevity, desig- 
1 Contributions from the Zoölogical Laboratory of the Museum of Comparative 
Zoology at Harvard College, E. L. Mark, Director, No. LXXXV, 
2 In the Anura, where there is no spinal nerve emerging anterior to the atlas, 
the so called first spinal nerve emerges between the first and second vertebra, and 
is homologous to the second nerve of Urodela 
VOL. XXXI. — NO, 4. 
