4 
MacLean 
Figure 4. Reproduction of first figure of Elliot 
Smith’s paper of 1918/1919, illustrating a frontal 
section through the forebrain of the tuatara 
{Sphenodon punctatum). The diagram is useful 
for suggesting how a proliferating area repre- 
sented by the U-shaped collection of cells (arrow 
at a) may have been influential in determining the 
divergent evolution of birds and mammals. It was 
as though a proliferation of cells in the left limb 
of the U had led to a piling up of ganglia on 
ganglia in birds, whereas activity in the right 
limb resulted in a burgeoning of cortex in mam- 
mals (see text). H’-H° designate areas to which 
Elliot Smith gave the name “hypopallium,” and 
which J.B. Johnston had previously referred to as 
the “dorsal ventricular ridge.” The lateral striate 
artery marks the boundary between the ridge and 
the underlying striatal complex, which is found 
as a constant feature in the brains of reptiles, 
birds, and mammals. HIP identifies the hippo- 
campal formation, which becomes a principal site 
of unfolding of the limbic cortex. Other abbrevia- 
tions; b, junction of Hip. and P.P., A.P., area 
pyriformis [sic]; P.B., paraterminal body; P.P., 
parahippocampal pallium. 
and a wealth of clinical observations, there 
is no clear understanding of the precise 
functions of the caudate-lenticular complex 
per se, as distinct from the other brain areas 
with which it is in functional connection . . 
(p. 380). The traditional clinical view that 
the striatal complex is primarily “motor” 
in function is not supported by findings that 
large, unilateral or bilateral lesions of its 
various parts may result in no obvious dis- 
ability (Denny-Brown, 1962; Kennard, 1944; 
Laursen, 1963; MacLean, 1972; Mettler, 
1942; Meyers, 1942; Ranson and Berry, 
1941; and Wilson, 1914). 
Since the opening of the present laboratory 
in 1971, a primary purpose has been to 
conduct comparative studies on animals for 
testing the hypothesis that the striatal com- 
plex plays a basic role in the organized ex- 
pression of species-typical, communicative 
behavior. 
COMMUNICATIVE BEHAVIOR 
Human communicative behavior can be 
classified as verbal and nonverbal. Like 
Percy W. Bridgman, the physicist-philos- 
opher, people commonly assume that “most 
human communication is verbal” (1959). 
Contrary to the popular view, many behav- 
ioral scientists would place a greater em- 
phasis on nonverbal communication. 
Many forms of human nonverbal communi- 
cation show a similarity to behavioral pat- 
terns seen in animals ranging from reptiles 
to primates. Since it is inappropriate to refer 
to nonverbal communication of animals, 
another term is needed to refer to such be- 
havior. Consequently, I have used the word 
“prosematic,” derived from the Greek {irpo- 
(Trjfia) and applying to rudimentary signaling, 
for referring to communication involving 
any kind of nonverbal signal — vocal, bodily, 
chemical (MacLean, 1975a, 1977a). 
It has been the special contribution of 
ethology to provide the first systematic in- 
sights into the “semantics” and “syntax” 
of prosematic behavior of animals. Some- 
what comparable to words, sentences, and 
paragraphs, prosematic behavior becomes 
meaningful in terms of its components, con- 
structs, and sequences of constructs (Mac- 
Lean, 19776). 
Since the patterns of behavior involved in 
self-preservation and the survival of the 
species are generally similar in most terres- 
trial vertebrates, it is not meaningful for 
our present purposes to refer to them in the 
traditional manner as species-specific behav- 
ior. But since various species perform these 
behaviors in their own typical ways, it is 
