The Medial Lemniscus in Lizards 
95 
Figure 3. Nissl and locus of degeneration in nucleus tentatively designated as the inferior olive (OI-). 
traced beyond the mesencephalon in any 
nonmammalian vertebrate (Christensen, 
1917; Huber and Crosby, 1926; Shanklin, 
1930). The important question of the exist- 
ence of a ventral tier group of the thalamus 
in nonmammalian forms has thus remained 
unanswered. Huber and Crosby (1926), 
working with the alligator, were able to 
trace crossed fibers arising from the nucleus 
gracilis and nucleus cuneatus and accumu- 
lating into a bundle which appeared to turn 
forward. In their nonexperimental material, 
however, it was not possible to trace it to 
the thalamus, and the other projections have 
also remained unknown. 
Although the dorsal column nuclei and 
the medial lemniscus were thought to be 
absent in amphibians (Ariens Kappers et 
al., 1936, p. 190), considerable evidence for 
their presence has recently been reported 
(Ebbesson, 1976). This, together with the 
findings reported here, suggests that somato- 
sensory information does indeed get to the 
forebrain and that paths for tactile discrimi- 
nation and well-developed proprioceptive 
impulses are not necessarily as recent, phylo- 
genetically, as hitherto believed (Ariens 
Kappers et al., 1936). 
The Inferior Olive 
The major medullary target of medial 
lemniscal fibers in mammals is the medial 
and the dorsal accessory nuclei of the in- 
ferior olivary complex (Hand and Liu, 1966; 
Merest, 1967 ; Ebbesson, 1968 ; Boesten, 
1971 ; Jane and Schroeder, 1971 ; Schroeder 
and Jane, 1971 ; Hazlett et al., 1972; Boesten 
and Voogd, 1975; and Groenewegen et al., 
1975). Since an inferior olivary complex 
has not been identified in reptiles, it is not 
possible to say with certainty whether the 
poorly differentiated nucleus identified as 
01? in Figs. 3-4 is indeed a homolog of its 
mammalian counterpart, but it appears 
