SCIENCE. 
73 
SATURDAY, AUGUST 14, 1880. 
CONTRIBUTIONS TO ENCEPHALIC ANATOMY. 
BY E. C. SPITZKA, M.D. 
Having, through a piece of good fortune, come into 
the possession of a living iguana, and thence obtained 
the brain and cord in a perfectly fresh condition, I 
was enabled to make a study for the first time of the 
remarkable brain of this saurian. 
As regards the exterior of the encephalon, it pre- 
sents nothing very different from that of any other 
higher reptile. On a lateral view, however, it exhibits 
a much acuter basilar incurvation, approximating to 
the bird’s brain in this respect. As in birds, also, the 
optic nerves leave the skull directly on emerging from 
the chiasm. It is remarked also that the optic lobes 
are far larger than in any reptile or bird thus far ex- 
amined by anatomists • in fact, excluding the case of 
the finny tribes, it may be said that the iguana pos- 
sesses the largest optic lobes in the animal kingdom. 
They are as massive in their grey and white tissues, 
and nearly as voluminous as the cerebral hemispheres. 
The olfactory lobes and bulbs offer nothing special 
for consideration. 
On a transverse section through the cerebral hemi- 
spheres, I am able to identify the component parts of 
the cornu ammonis of the mammalia. It appears 
that the medial thin wall of the cerebral vesicle corre- 
sponds, with its layer of closely packed pyramidal 
nerve cells, to the stratum corporum nervorum arcto- 
rum of Kuppfer, and it is indeed separated from the 
cortical layer of the convexity, which I believe to cor- 
respond, as far as the thin part extends, to the sigma 
of the cornu. At the lower end of the thin-walled 
vesicle, where a transition of nerve fibres from 
the stratum corporum nervorum arctorum (?) takes 
place, to the thalamus, and which therefore corre- 
sponds to the fornix, there is an accumulation of 
molecular nerve substance, projecting outwards into 
the ventricular cavity. This may represent one of the 
thalamic tubercles ; I regard it as much more proba- 
ble, however, that it corresponds to the body of the 
so-called fascia dentata. 
Now, in sections exhibiting the above features, I 
find also another which is highly important, in so far 
as it tends to overthrow another one of the dicta on 
whose strength the sauropsidean and mammalian 
brains are distinguished. Immediately underneath 
the median longitudinal fissure, but over the third 
ventricle, there passes a fasciculus of white fibres, 
uniting the' two hemispheres, and particularly that 
portion of each which corresponds to the cornu am- 
monis. This is unquestionably the corpus callosum, 
whose first appearance in the embryo and the lower 
mammalia we know to be intimately associated with 
the development of the cornu ammonis. 
But it is when we reach the mesencephalon and 
the region posterior to it, that we discover the most 
remarkable features of this brain. 
As in some other saurians, the cerebellum instead 
of being curved backward, and constituting a cap 
over a part of the lateral ventricle, as in the alligator 
and chelonia, is bent forward, and bound to the 
posterior face of the optic lobes by the arachnoid 
filaments. On separating and drawing it backward, 
thus making it correspond artificially in position with 
the cerebellum of the alligator, we find that between 
the optic lobes and the cerebellum there are two pairs 
I of tubercles. 
One of these pairs, which I have found as a con- 
cealed mass in turtles, and as a very distinct elevation 
in the alligator, ophidia and pseudopus, I was familiar 
with, and I had no hesitation in describing it as the 
post-optic ganglia corresponding to the posterior pair 
of the corpora q'uadrigemina. The other was at first 
new to me, but after a careful comparative study I 
found that it was nothing but an unusually large, and 
therefore more prominent representative of a gang- 
lionic mass which I have noticed in fair development 
in the turtle, and which is even represented in an 
atrophic condition with the mammalia. As the pair 
of tubercles in the iguana lies intermediate to the 
optic and post-optic lobes, I propose for it the name 
of inter-optic lobes. 
On a dorsal view these different parts lie about as 
follows : In front are the massive optic lobes touching 
each other broadly on the middle line, so that their 
posterior margins form a continuous semi-lunar curve, 
convex behind. Behind each optic lobe, and bulging 
out somewhat, laterally, we have the smaller but dis- 
tinct post-optic lobes, which fail to come in contact 
in the median line, so that a shallow groove would 
separate them, if it were not filled out by another 
structure now to be described. 
If we imagine the median furrow separating the 
optic lobes prolonged between the post-optic lobes, 
and crowd two little pea-shaped eminences on each 
side of this imaginary median line, so that the latter 
are bounded in front by the optic lobes, on the out- 
side by the post-optic lobes, and behind by the cere- 
bellum, we will have the precise situation of the 
inter-optic lobes. These eminences are not so re- 
markable for their absolute size (their surface extent 
being only half that of the optic lobes) as for the 
distinctness of their demarcation. I have obtained 
sections through their posterior third, in which these 
bodies are shown to be absolutely free. 
Other sections further forward show that these 
ganglia crop out of a specialized division of the cen- 
tral tubular grey of the aqueduct, and that the visible 
eminences do not represent the true extent of the 
ganglia. 
The trochlearis nerves arise behind the inter-optic 
lobes, and passing forwards and downwards, lie in the 
furrow between the optic and post-optic lobes, as in 
other reptiles. It is well known that in the mammalia 
they pass down behind the post-optic lobes. I look 
on this as an incidental and insignificant variation. 
The remainder of the isthmus shows nothing 
especially noteworthy. The remarkable size of the 
oculo-motor nuclei, and the gigantic dimensions of 
their almost star-like multipolar nerve-cells, merits 
mention, as well as the fact that in this animal the 
nuclei of the third and fourth pairs constitute a com- 
mon cell mass, unlike the relation in the mammalia, 
and that the third and fourth pairs arise almost in the 
