112 
Cruce 
Degenerating fibers were seen coursing 
through lamina X or the dorsal gray com- 
missure (Figs. 3, 4, hE, and 6A) and the 
ventral accessory white commissure (Fig. 
65) toward the contralateral side of the cord. 
There the degeneration took on the appear- 
ance of preterminal aborizations and ter- 
minals and was confined to the medial parts 
of laminae VII and VIII and medial lamina 
IX (Fig. 6G). No degeneration was present 
in the lateral part of the spinal gray on the 
contralateral side (Fig. 6F). 
Smaller spinal lesions which avoided the 
MLF and the ventromedial funiculus (Fig. 
4) created a similar pattern of degeneration. 
The density of degenerating fibers in medial 
regions of the ventral horn was decreased 
but it was still more intense than that in 
lateral regions. The smallest spinal lesion, 
confined only to the dorsolateral funiculus 
produced bilateral sparse degeneration, prob- 
ably preterminal and terminal in nature, 
which was confined primarily to the lateral 
parts of laminae V, VI, and VII, ipsilaterally, 
and the medial parts of these laminae, con- 
tralaterally (Cruce et al., 1976). A similarly 
small lesion, confined to the ventromedial 
funiculus resulted in dense preterminal and 
terminal degeneration which was found only 
in lamina VIII and medial lamina IX, bi- 
laterally (Cruce et al., 1976). A lesion which 
included the ventrolateral funiculus caused 
additional ipsilateral degeneration in the 
ventrolateral parts of lamina VII. 
Brain Stem Chromatolysis 
It is beyond the scope of this paper to 
describe the cytoarchitecture of the lizard 
brainstem. An excellent classical review is 
available in the work of Ariens Kappers 
et al., (1936). More recent studies are cov- 
ered in papers by Cruce and Nieuwenhuys 
(1974) and Donkelaar and Nieuwenhuys 
(1978). The lizard brainstem contains essen- 
tially the same cell groups as other reptiles. 
Most of the brainstem cell groups seen in 
reptiles are also seen in mammals. 
Following a complete hemisection at the 
first spinal segment, typical retrograde 
changes (swelling of the cell body, clearing 
of the central Nissl substance, and eccentric 
nucleus) indicative of axonal injury were 
seen in cells of many brainstem nuclei 
(Cruce et al., 1976; Cruce and Newman, 
unpubl. observ.). The chief nuclei involved 
were the interstitial nucleus and red nucleus 
of the mesencephalon, the lateral tegmental 
nuclei of the metencephalon, the ventro- 
lateral and dorsolateral vestibular nuclei, 
the medial reticular nuclei of the meten- 
cephalon and myelencephalon, the myelen- 
cephalic raphe nucleus, and the nucleus of 
the solitary tract. 
By comparing the results from different 
small lesions of the funiculi at the first 
spinal segment, it was determined that the 
dorsolateral funiculus contains descending 
fibers central ater ally from the red nucleus, 
a lateral tegmental nucleus, and the solitary 
nucleus and ipsilaterally from a lateral teg- 
mental nucleus and from a portion of the 
myelencephalic reticular formation ; the ven- 
trolateral funiculus contains fibers bilaterally 
from portions of the myelencephalic reticular 
formation and the myelencephalic raphe 
nucleus ; and the ventromedial funiculus con- 
tains fibers ipsilaterally from the interstitial 
nucleus, the metencephalic medial reticular 
formation, and the ventrolateral vestibular 
nucleus and contralaterally from the dorso- 
lateral vestibular nucleus. 
Behavioral Observations 
During surgery, as the lesion knife ap- 
proached the midline, respiratory movements 
of the ribcage were abolished on the ipsi- 
lateral side. When there was no postoperative 
recovery of ipsilateral respiration, postmor- 
tem histological examination of the lesion 
revealed that the medial longitudinal fasci- 
culus (MLF), which is located bilaterally 
adjacent to the midline, was transected 
ipsilaterally (Fig. 3). 
Upon recovery from anesthesia following 
a complete hemisection, there was a marked 
curving of the animal’s neck, trunk, and tail 
