Lizard Descending Pathways 
119 
way when comparing vertebrate classes are 
not as instructive as the differences in how 
a given species employs the motor systems 
which it has to use in order to cope with its 
environment. Fine morphological differences 
in the spinal cord, such as position and 
orientation of the dendritic tree of target 
neurons and the number and position of 
descending fiber boutons upon these den- 
drites, particularly when correlated with 
different physiological and behavioral capa- 
bilities, are likely to be fruitful avenues to- 
ward understanding how the nervous system 
works. Eventually such studies may lead to 
an understanding of how motor systems 
have evolved, but this understanding will 
require the collection of data from many 
more species than have currently been 
studied. 
ACKNOWLEDGMENTS 
This research was conducted according to prin- 
ciples enunciated in the “Guide for Laboratory 
Animal Facilities and Care” prepared by the Na- 
tional Academy of Sciences — National Research 
Council. 
Some of the work reported in this paper was in- 
itiated while the author was an NIH postdoctoral 
fellow (1F-10NA-2567-01-NSRB) in the Depart- 
ment of Anatomy, University of Wisconsin, Madison. 
The work there was supported, in part, by the fol- 
lowing NIH grants: NS-09167, ROl-NS-06662, and 
5 POl— NS-06225. In addition, the work was more 
recently supported, in part, by NSF grant BNS75- 
09643 and GRS grant 5-S01-RR-05351-14 to 
Howard University. 
Dr. J.A.F. Cruce and Dr. D.B. Newman reviewed 
the manuscript, and Ms. B. Alexander, Mr. T. Nevin, 
and Mr. S. Stefl provided technical assistance. 
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