The nucleus of BELLONCI in birds - DWC

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1100 upper part of a cell plate, which for the rest gives rise to the ventral lateral geniculate 1) , and thus would belong to the ventral thalamus. According to KUHLENBECK (1937), working also with the chick, the nucleus lateralis anterior, however, is a rostral differentiation of the primordium of the dorsal lateral genieulate, which belongs to the dorsaI' thalamus. In amphibians as well as in reptiles and mamma Is the nucleus of BELLONCI is an ellipsoid, whose major axis surpasses the langer of the minor axes two times or more in length. In the first class the major axis of the ellipsoid is directed sagittaIly, whereas in reptiles and mammals it is situated in a transverse plane. In the previous paper I explained th is difference by a turning of the nucleus through 90°. It may as well be, however, that it has been brought about by a compression in sagittal direction. Like the nucleus of BELLONCI also the nucleus lateralis anterior is an ellipsoid, with, however, but a slight difference in length between the major axis and the langer of the minor axes. As to the histologieal structure of the nucleus of BELLONCI, in amphibians this nucleus is a dense ma ss of neuropil, with but a few cells within it, almost all of these being ~ituated outside the neuropil, viz., on its medial side. In reptiles and mammaIs, however, the cells lie within the neuropiI. The avian nucleus lateralis anterior is likewise a dense ma ss of neuropil. with the cells within it. A comparison of the connections of the two nuclei also strongly speaks in favour of their homology. In the previous paper it was set forth that the chief supply to the nucleus of BELLONCI (in amphibians and crocodilians at least) was by the tractus olfacto~habenularis Jateralis 2) , and that a contribution from the optie might be deemed certain in amphibians, prdbable in reptiles, and not excluded in mam mals. The connection with the optic was confirmed of late by STRÖER (I 939) , who found that in specimens of Triturus taeniatus wh ere in early stages the primordium of one eye was extirpated, the neuropil of BELLONCI on the heterolateral side was smaller than on the other. As to the connections of the nucleus lateralis anterior, when describing this nucleus in the sparrow and dove, lalready expressed as my opinion 1) As set forth below. the nucleus lateralis anterior is identical with RENDAHL's nucleus fasciculi septi (labelled ä by him). while- the ventral lateral geniculate of KUHLENBECK and us corresponds with RFNDAHL's corpus geniculatum thalamicum. 2) In the previous paper I distinguished in crocodilians a tractus olfacto-habenularis lateralis anterior and posterior. identifying the former with the tractus olfacto-habenularis lateralis of Miss CROSBY (1917) and the latter with her tractus olfacto-habenulari~ posterior. As I now perceive. the latter identification is not correct. The tractus oHactohabenularis posterior of Miss CROSBY arises near the posterior end of the hemisphere from the nucleus of the lateral olfactory tract and the ventro-medial nucleus. The fibres. however. described by me as tractus dJfacto-habenularis lateralis posterior. from an unknown souree ascend through the forebrain bundIe to the ~tria medullaris. They have already been seen by UNGER (1911) (his tractus transversalis taeniae) in crocodilians and by CAIRNEY (1926) in Sphenodon. Thus the two terms proposed by me have to be dropped.
1101 that its chief supply is by fibres coming from ventromedial and ascending to the stria medullaris, which I interpreted as the tractus olfacto-habenularis lateralis. I could not decide, however, in my WEIGERT-PAL preparations wh ether the optie tract, the tractus isthmo-optieus and the ramus dorsalis of the tractus septo-mesencephalicus, all of which are closely applied to the nucleus lateralis anterior, actually synapse with it. Regarding this, however, the Japanese SHIINA (1932), in his monograph on the nucleus lateralis anterior, gives some, though not very convincing, information. Partlyon the basis of normal preparations (WEIGERT-PAL), partly of MARCHI and G UDDEN experiments, he came to the conclusion that fibres of the ramus dorsalis of the tractus septo-mesencephalicus pass only through the nucleus, but that op tic fibres actually end here. Contrary to HUBER and CROSBY (1929), who did not see the tractus olfacto-habenularis lateralis, SIiIlNA described these fibres in all the birds, investigated by him, but regarded them as arising in the nucleus lateralis anterior and running in medial direction, partly to join the supraoptie decussations. Doubtless, however, the fibres in question ascend to the stria medullaris, as described and figured here for the dove (figs. 5, 6) . Finally it may be mentioned that the only connection HUBER and CROSfW (1929) name for the nucleus lateralis anterior is their tractus thalamofrontalis intermedia lis (better intermedius) . S~IIINA confirms this both in norm al and MARCHI preparations and, moreover, on the same basis, mentions a connection with the tractus thalamo-frontalis lateralis. In my WEIGERT-PAL preparations I can confirm neither of these statements. From this discussion of the connections of the nucleus lateralis anterior of birds thus much seems to be su re that the tractus olfacto-habenularis lateralis provides the chief supply, and that a connection with the optie is very probable, just the same conclusions we arrived at for the nucleus of BELLONCI of amphibians and reptiles. Thus, with the possible ex cept ion of embryologieal development, all criteria for the homology of nuclei available: position in the adult, connections, histologieal structure, and shape are in favour of the homology advocated by us. The only other interpretation so far offered of the nucleus lateralis anterior of birds, is by KUHLENI3ECK (1937). As mentioned above, according to him, in the chiek this nucleus is a rostral differentiation of the same cell plate whieh for the rest gives ri se to the dorsal lateral genieulate. H, moreover, it could be proved that the nucleus lateralis anterior receives optie fibres, this nucleus should simply be called pars rostralis corporis genieulati dorsalis. The anterior part of the optie tract, however, whieh, according to KUHLENBECK, possibly supplies the nucleus lateralis anterior in all probability is nothing but our tractus olfacto-habenularis lateralis. While, apart from KUHLENRECK'S, no attempts have been made to find homologues for the nucleus lateralis anterior of birds, either lowel' or higher in the scale of vertebrates, it has been tried several times to homologize the nucleus of BELl.ONCI of amphibians or ovalis of reptiles
Page 1 and 2: Anatomy. - The nucleus of BELLONCI
Page 3 and 4: 1095 tr. sept~mesel1e ventr. I at .
Page 5 and 6: 1097 nucl. mes. I. d. c., nucleus m
Page 7: 1099 by H UBER and CROSBY (their co
Page 11 and 12: 1103 lateralis anterior relative to
Page 13 and 14: 1105 lateralis anterior. They faile

The nucleus of BELLONCI in birds - DWC

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