Forebrain and Midbrain of Lizards 
31 
similar results in Tupinambis. At present, 
nothing is known regarding septal efferents 
in lizards, but it is likely that the septal 
nuclei project to the medial cortex and parts 
of the hypothalamic complex and tegmentum 
as in mammals. 
There is considerable variation in the size 
and differentiation of the septal complex in 
lizards, but detailed cytological, histochemi- 
cal, and connectional studies on taxa that 
show considerable septal variation, such as 
Gekko and Iguana, must be carried out be- 
fore this variation can be described with 
assurance. 
RESULTS AND DISCUSSION: 
DIENCEPHALON 
Studies dealing with the organization of 
the reptilian diencephalon can be divided 
chronologically into two groups. Prior to 
1926, a number of investigators began initial 
descriptions of many of the cell groups and 
fiber systems that constitute the dienceph- 
alon of reptiles (Stieda, 1875; Bellonci, 
1888 ; C. L. Herrick, 1893a, 18936 ; Meyer, 
1893; Rabl-Riickhard, 1894; P. Ramon, 
1896; Edinger, 1899; Gisi, 1908; C. J. Her- 
rick, 1910; de Lange, 1913). These studies 
resulted in a wide range of descriptions and 
a bewildering array of terms which some- 
times described totally different nuclei under 
the same name, or the same population of 
cells in different taxa with totally different 
names. In 1926, Huber and Crosby described 
the diencephalon of Alligator mississipiensis 
in a clear and concise manner, and subse- 
quent studies have relied heavily on the 
nomenclature presented in that study. 
Since 1926, a number of studies have dealt 
with the diencephalon of lizards (Shanklin, 
1930; Frederikse, 1931; Kuhlenbeck, 1931; 
Senn, 1968; Butler and Northcutt, 1973; 
Cruce, 1974). Butler and Northcutt (1973) 
and Cruce (1974) have reviewed all of the 
earlier studies and have attempted to clarify 
the various earlier nomenclatures. The no- 
menclatures proposed by these last two stud- 
ies agree, in large part, and will be utilized 
in the present report. Cruce’s description of 
the hypothalamus is more detailed than that 
reported by Butler and Northcult, and the 
overall treatment of the hypothalamus by 
Cruce is clearly superior. 
Epithalamus, Thalamus, and Hypothalamus 
The diencephalon of reptiles has been di- 
vided into epithalamus, thalamus, and hypo- 
thalamus since the studies of Edinger (1899) 
and C. J. Herrick (1910). The epithalamus 
consists of medial and lateral habenular nu- 
clei and the habenular commissure (Fig. 12). 
Little is known regarding the connections 
of the habenular nuclei. Hoogland (1975) 
has suggested, on the basis of preliminary 
autoradiographic studies, that a portion of 
the striatum of Tupinambis projects to the 
habenular nuclei. Similar projections have 
been reported in mammals (Nauta and Meh- 
ler, 1966; Nauta, 1974). Projections from 
other telencephalic centers probably exit via 
the stria medullaris, but no experimental 
studies have been conducted on this path- 
way. As in other vertebrates, a well-devel- 
oped fasciculus retroflexus exists between 
the habenular nuclei and the interpeduncular 
nucleus. 
Little attention has been directed toward 
analysis of the reptilian hypothalamus. This 
brain region was first described by Edinger 
(1899). Crosby and Showers (1969) and 
Cruce (1974) presented comprehensive re- 
views of the literature and have extensively 
described the subdivisions of the hypothal- 
amus in reptiles. The same major divisions of 
the hypothalamus can be recognized in rep- 
tiles as in other amniotic vertebrates, and 
the reader is referred to Cruce’s paper for a 
detailed account of this region. Again, little 
is known regarding the connections of the 
reptilian hypothalamus. Our understanding 
of the neural substrates of reptilian behavior 
cannot be expected to progress very far until 
much more data have accumulated on the 
organization and function of the reptilian 
hypothalamus. 
