Lizard Descending Pathways 
115 
to the contralateral side. Sometimes this 
curvature was observed when the animal was 
resting. When the animal tried to run, the 
accentuated curvature resulted in a circling 
to the contralateral side, or there was a 
complete cessation of movement with the 
animal coiled contralaterally. During loco- 
motion the normal wave of side-to-side 
flexion of the trunk, which travels through 
the body as an aid to increasing stride and 
leverage of the limbs (Snyder, 1952 ; Bellairs, 
1969), was lost. The tail was also no longer 
used as a whip in defense. Thus, there ap- 
peared to be a loss or weakening of activity 
in ipsilateral trunk muscles. 
Slow walking was abnormal, partly due 
to the loss of trunk flexion, but also due to 
weakness and abnormalities of movement in 
the limbs. The sacral trunk tended to roll to 
the ipsilateral side as if the ipsilateral hind- 
limb was unable to support the body at the 
hip. While the animal was able to stand on 
all limbs, it was unable to support its body 
weight on either forelimb alone, particularly 
when the limb was extended backwards. 
There was a tendency of the resting animal 
to extend its ipsilateral forelimb and to fall 
over with the contralateral forelimb collapsed 
under the body. During slow walking, the 
ipsilateral forelimb was sometimes passively 
dragged in the extended position. The animal 
could also stand on, and locomote with, all 
limbs, though it appeared to tire quickly. 
Animals with less than complete hemisec- 
tions showed losses of motor activity, except 
bilateral respiration (see above), though the 
losses were less severe than those in animals 
with complete hemisections. There was some- 
times a slight ability to bend the neck past 
the midline, but strength in ipsilateral trunk 
muscles was greatly diminished compared to 
that seen contralaterally. 
DISCUSSION 
Spinal Cord Organization 
Rexed’s (1952, 1954, 1964) analysis of the 
cytoarchitecture of the cat spinal cord has 
frequently been applied to other mammalian 
species, e.g., tree shrew (Shriver and Noback, 
1967), opossum (Martin and Dom, 1970), 
squirrel monkey (Harting and Noback, 
1970), and chimpanzee (Noback and Sime- 
nauer, 1970). Cytoarchitectonic analyses of 
the avian spinal cord (Akker, 1970; Brink- 
man and Martin, 1973) have revealed a simi- 
larity to the mammalian structure, and re- 
cently Leonard and Cohen (1975) have 
shown that the organization of the gray 
matter in the pigeon spinal cord is quite 
like that described by Rexed in the cat. An 
organization which resembles Rexed’s lami- 
nae has also been found in the lizard spinal 
cord (Cruce, 1978), thus suggesting that the 
laminar organization of the spinal cord may 
be a general feature of many vertebrates. 
The Golgi picture of the organization of 
axons and dendrites of neurons intrinsic to 
the Tegu lizard spinal cord is similar to that 
seen by Ramon Y Cajal (1891, 1909-1911) 
in the lizard, Lacerta, and by Banchi (1903) 
in the turtle, Emys. In some respects it is 
also similar to that seen in mammals (e.g., 
Matsushita, 1970 a, 6), i.e., neurons of lamina 
VII are related ventrally and laterally to 
neurons of lateral lamina IX and the lateral 
funiculus, while neurons of lamina VIII are 
related ventrally and medially to medial 
lamina IX, the ventral funiculus and the 
commissures. Since lateral lamina IX con- 
tains motoneurons innervating the limbs, and 
medial lamina IX contains those innervating 
the trunk (Cruce, 1974), it may be suggested 
that interneurons of lamina VII and VIII 
are involved in the integration of limb and 
trunk movement, respectively, as has been 
proposed to be the case in mammals (Sterling 
and Kuypers, 1968). 
A notable difference between reptilian 
and mammalian spinal organization is re- 
vealed by Golgi analysis of transverse sec- 
tions. Whereas mammalian spinal motoneu- 
rons exhibit a uniform multipolar dendritic 
pattern (Testa 1964), Tegu lizard lateral 
motoneurons possess two primary dendrites 
— a medial one and a lateral one. This den- 
dritic configuration is reminiscent of the 
structure of the goldfish Mauthner cell 
