The nucleus of BELLONCI in birds - DWC

1097
nucl. mes. I. d. c., nucleus mesencephalicus nucl. post.-interm., nucleus posterolateralis
pars dorsalis centralis.
intermedius.
nucl. mes. I. d. s., nucleus mesencephalicus nucl. post.-ventr., nucleus postero-ventralis.
lateralis pars dorsalis superficialis. nucl. sept.-hipp., nucleus septo-hippocamnucl.
periv. m. acc., nucleus periventricularis palis.
magnocellularis accessorius (see KUROT- tr. gen.-front. ventr., tractus geniculosu,
1935). frontalis ventralis (see FREY, 1937).
nucl. periv. m. pr., nucleus periventricularis tr. sept.-mes. r. b. C., tractus septo-mesenmagnocellularis
principalis (see KUROT- cephalicus ramus basalis caudalis.
su, 1935).
by a ma ss of loosely arranged fine myelinated fibres th at seem to come
Erom the dorsal supraoptic decussation (figs. I , 2). These fibres diverge
in the direction of the nucleus, embrace and traverse it, but at its lateral
side again collect. Farther they could not be followed with certainty in the
sparrow. In the dove, wh ere they are much bet ter studied, we shall revert
to them.
Also in this bird the nucleus of BELLONCI is an ellipsoid (figs. 5, 6) , but
here the major axis, in contradistinction with the sparrow, where it lies in
a transverse plane, is directed sagittally, while the longer of the minor
axes, which IS but little shorter than the major axis, extends almost
vertically.
In the dove the nucleus of BELLONCI shows about the same relationships
to the neighbouring nuclei as in the sparrow, but those to the neighbouring
and possibly synapsing tracts are somewhat different, in that the ramus
dorsalis of the tractus septo-mesencephalicus is only in contact with the
oral extremity of the nucleus. Very soon this tract, leaving the nucleus,
turns dorsomedially, and runs caudalward along the surface of the brain
(figs. 5, 6) .
No more than in the sparrow the origin of the fibres coming from
ventromedial could be ascertained in the dove, though they are far more
numerous here. All that I can say is that they seem to come from the
dorsal supraoptic decussation. Part of them swing medially across the
dorsal peduncle of the lateral forebrain bundIe and join the stria medullaris,
another part do so with the ramus dorsalis of the tractus septo-mesencephalicus.
The latter, however, is connected by a compact strand of fibres,
coursing along the surface of the brain, with the stria medullaris (fig. 6) .
These connecting fibres, in part at least, may be the same as that portion
of the fibres coming from ventromedial which joined the tractus septomesencephalicus.
Evidently the loose fibre mass coming from ventromedial represents the
tractus olfacto-habenularis lateralis, which originates in the preoptic and
hypothalamic regions. This fibre ma ss has not been seen by HUBER and
CROSBY (1929) , who state that they could not identify a tractus olfactohabenularis
lateralis in birds. The strand of fibres, however, connecting
the septo-mesencephalic tract with the stria medullaris, has been observed
Proc. Ned. Akad. v. Wetenseh., Amsterdam, Vol. XLIII, 1940. 71