The Lacertilian Forebrain 
75 
In summary, the reptilian dorsal cortex is 
the recipient of ascending projections from 
both the dorsal lateral geniculate nucleus and 
the more medially located nucleus dorso- 
lateralis anterior of the thalamus. On the 
basis of its position and its apparent lack of 
sensory afferents, the latter nucleus may 
correspond to part of the anterior nuclear 
group in the thalamus of mammals. Efferent 
projections of dorsal cortex have been traced 
to the dorsal lateral geniculate nucleus and 
to an anterior nucleus in the thalamus, sep- 
tum, and hypothalamus. Thus, on the one 
hand, the dorsal cortex appears to correspond 
to part of neocortex, while on the other it 
appears to correspond to part of the mam- 
malian limbic system. 
One possible resolution of this problem lies 
in noting that in lizards, for example, medial 
and dorsal divisions of dorsal cortex can 
easily be recognized. In birds, the afferent 
projections to the Wulst of nucleus dorso- 
lateralis anterior and the principal optic 
nucleus terminate in nonoverlapping zones 
in the medial and lateral portions of the 
Wulst, respectively, and it is the lateral 
Wulst which projects into the DVR and re- 
ciprocally to the principal optic nucleus. The 
medial Wulst is juxtaposed to the medial 
hippocampal cortex (Karten et al., 1973), as 
is the medial part of dorsal cortex in reptiles. 
Thus the explanation of the differing results 
in reptiles may simply be that the dorsal 
cortex is composed of two very different 
parts, a medial limbic portion and a lateral 
portion homologous to some cell populations 
in the mammalian neocortex, and that these 
two parts are differentially developed in 
various species. 
An alternative explanation, however, is 
that, while in birds the medial and lateral 
parts of the Wulst have evolved separate 
connections and functions, the entire dorsal 
cortex in lizards is homologous as a field to 
parts of both the mammalian neocortex and 
hippocampal formation. In either case, could 
the interhemispheric commissural connec- 
tions of dorsal cortex found in Gekko, which 
travel in the dorsal pallial commissure, then 
correspond to connections of mammalian 
neocortex via the corpus callosum? We must 
consider the evidence regarding the evolution 
Figure 3. Schematic representation of some of the current data on the afferent and efferent connections of 
the dorsal cortex and the dorsal ventricular ridge (DVR) in reptiles and birds. For turtles, lizards, and 
snakes, the diagrams are bilateral representations; afferent connections are shown on the left of each dia- 
gram and efferent connections on the right. For crocodiles and birds, the diagrams are unilateral. In all 
cases, medial cortex, dorsomedial cortex, and lateral cortex have been omitted, as have connections caudal 
to the level of the diencephalon. Small circles represent cell bodies; v’s, axon terminals; and lines, axons. 
The position of cell bodies or terminals within structures is not necessarily anatomically precise, except in 
the cases of afferents to the DVR (L and E in birds) and the connections of the medial versus the lateral 
parts of the Wulst (MW and LW) in birds. An X placed on a line indicates that this projection has been 
found to be absent. 
Abbreviations. Large letters indicate the structures diagramed as follows: A, anterior commissure; D, 
dorsal cortex; DLA, nucleus dorsolateralis anterior; DVR, dorsal ventricular ridge; E, ectostriatum ; G, 
nucleus geniculatus lateralis pars dorsalis; H, hippocampal commissure; Hy, hypothalamus; L, fields L 
of Rose; LW, lateral Wulst; MW, medial Wulst; Na, a rostral extension of Warner’s nucleus anterior; 
OPT, nucleus opticus principalis thalami; OV, nucleus ovoidalis; R, nucleus rotundus; Re, nucleus re- 
uniens; S, septum. 
Small letters placed next to lines indicate the references for the data as follows: B, Butler, 1976; D, Distel 
and Ebbesson, 1975; F, Foster et al., 1976; H, Hall and Ebner, 1974; HE, Hall and Ebner, 1970b; Hp, 
Halpern, 1974, 1976; K, Karten, 1968; KH, Karten, et al., 1973; L. Lohman and Mentink, 1972; N, North- 
cutt, 1970; Pritz, 1974b, 1975; S, Sligar and Voneida, 1976; U, Ulinski, 1975; V, Voneida and Ebbesson, 
1969; W, Ware, 1974; Z, Zeier and Karten, 1973. 
The intent of this figure is twofold. It provides a summary of current data and demonstrates the lack of 
information on some pathways in various groups, e.g., the connections of dorsal cortex in caiman and 
thalamotelencephalic connections in snakes. Secondly, and more importantly, it demonstrates the problems 
which arise from considering “dorsal cortex” to be a single structure. This structure has afferent and effer- 
ent connections not only both with sensory relay nuclei of the dorsal thalamus, suggesting a correspon- 
dence to neocortex, but also with other areas, such as hypothalamus and septum, indicating that it is part 
of the limbic system of mammals. Thus, until individual cell populations and their specific connections are 
identified, and until sense can be made of the variation between groups and at the species level, little ad- 
ditional insight can be gained. 
