Lizard Descending Pathways 
109 
Figure 2. Camera lucida drawing prepared from Golgi-stained sections of lizard spinal cord. Different cel- 
lular regions of the ventral horn as determined in Nissl-stained sections are indicated by dashed lines. (A) 
Motoneurons of the medial lamina IX group. Note that dendrites of motoneurons are confined primarily to 
the medial lamina IX area and lamina VIII. (B) Motoneurons of the lateral lamina IX group. Note the 
extensive ramification of motoneuronal dendrites into laminae VII, VIII, and the medial lamina IX region. 
Reproduced from Cruce (1976), Brain, Behavior, and Evolution, with permission of the publisher. 
dendritic plexus. Although the longitudinal 
organization of lizard motoneurons has not 
yet been thoroughly analyzed, some pre- 
liminary observations have been made on 
horizontal and sagittal sections of Golgi- 
stained material. Motoneuronal dendrites are 
seen to run in the rostro-caudal axis through 
the column of motoneurons. Dendritic bun- 
dles, or thickets, such as are seen in the 
spinal cord of mammals (Scheibel and Schei- 
bel, 1970; Matthews, et al., 1971) and am- 
phibians (Stensaas and Stensaas, 1971) have 
not been recognized, but further analysis is 
necessary before these can be ruled out 
entirely. 
Descending Axon Degeneration 
Following a complete hemisection at the 
first spinal segment (Fig. 3) degenerating 
fibers in the white matter were confined to 
the ipsilateral side in three major groups: 
the medial longitudinal fasciculus (MLF), 
the dorsolateral funiculus, and the ventro- 
medial funiculus. In laterally placed lesions 
(incomplete hemisections) , fiber degeneration 
was absent in the MLF and greatly decreased 
in the ventromedial funiculus (Fig. 4). Fiber 
degeneration in the white matter decreased 
in proportion to the distance below the lesion, 
but was still present in caudal segments. 
In the gray matter, degenerating axoplasm 
was most intense in the medial part of lamina 
VII, in lamina VIII, and in medial lamina 
IX (Figs. 3 and 4). Much of this degenera- 
tion had a disorganized random appearance 
suggestive of preterminal aborizations and 
terminals (Figs. 5B, E, F, and 6D). Sparser 
degeneration was present in the lateral parts 
of laminae V, VI, and VII (Figs. 3 and 4). 
Some of this sparse degeneration was orga- 
nized in linear beads suggestive of axons 
(Figs. 5B and 6E) rather than terminal fields 
(but see below). Virtually no degenerating 
axoplasm was seen in the dorsal horn (Fig. 
5 A) or lateral lamina IX (Fig. 5(7). 
