The nucleus of BELLONCI in birds - DWC

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lateralis anterior relative to th is bundIe and nucleus. in the dove (figs. 5. 6)
at least. is not so very mueh different.
The seeond argument of HURER and CROSBY in favour of the homology
of the nucleus superficialis parvoeellularis and nucleus ovalis' is derived
from the eonneetions. Further study of their allig2tor material suggested
that there are fibres from the media I forebrain bundIe (or assoeiated with
it) which swing around the ventral side of the lateral forebrain bundIe and
into the nucleus ovalis. Sueh fibres would be homologous with the ramus
dorsalis of the septo-meseneephalic traet and the nucleus with the nucleus
of that traet or nucleus superficialis parvoeellularis. In the text-book of
KAPPERS. HUBER and CROSBY (1936) this statement. however. is not
repeated.
Contributory evidenee to a homology of the nucleus superficialis pa rvoeellularis
and nucleus ovalis. aeeording to HUBER and CROSBY. is found
in the distribution of optie fibres to both these nuclei. For the nucleus
ovalis. as set forth above. the presenee of optie connections may hold good.
but neither for the sparrow. nor the dove I ean eonfirm HUBER and
CROSBY's findings of optie fibres going to the nucleus superficialis pa rvoeellularis.
Our ehief objection against the homology advoeated by HUBER and
CROSBY. is that a connection of the nucleus superficialis parvoeellularis
with the tractus olfaeto-habenularis lateralis is entirely lacking. Moreover.
and this also is an important point. th is nucleus is voluminous and of
eonsiderable length. extending from about the beginning of the thalamus
to the posterior commissure. whereas the nucleus ovalis is small and
eonfined to the foremost part of the thalamus. And. as the latter is ehiefly
an olfaetory centre. it is extremely improbable that in the mierosmatie birds
it has developed into a strueture several times its size.
The seeond attempt. in which we are concerned. at homologizing eertain
thalamic centres is LE GROS CLARK's (1932) regarding the nucleus of
BELLONCI of amphibians as the forerunner of the dorsal lateral genieulate
of mammals. Already in reptiles. aeeording to LE GROS CLARK. a dorsal
lateral genieulate may be reeognized (the homologue eonsequently. in his
opinion. of the nucleus of BELLONCI of amphibians). In the American
alligator. aeeording to LE GROS CLARK. this centre is represented by a
differentiated lateral portion of the nucleus dorsolateralis anterior. described
by HUBER and CROSBY (1926). which is said by these authors to reeeive
some optie fibres. In Sphenodon these superficial eells even form a fairly
cireumseribed nucleus. whieh has been termed the dorsal nucleus of the
lateral geniculate body by CAIRNEY (1926) and DURWARD (1930).
Thus LE GROS CLARK's view about the fate of the nucleus of BELLONCI
of amphibians in amniotes (represented diagrammatieally in fig. 3 of his
paper. 1932) is entirely different from ours.
It must be ohjeeted to LE GROS CLARK that it is very doubtful if the
differentiated lateral portion of the nucleus dorsolateralis anterior of the