The nucleus of BELLONCI in birds - DWC

More documents

Recommendations

Info

1102 with centres of higher forms in a different manner from ours. If these attempts had been successfuI. they would. of course, invalidate one or more of the conclusions arrived at by us, and so we have to discuss them. Por want of spa ce, however, we can do so only with the two most important among these hypotheses, viz., those of HUBER and CROSBY (1929). which is the same as that of KAPPERS (1938), and of LE GROS CLARK (1932). HUBER and CROSBY (1929) are inclined to homologize their avian nucleus superficialis parvocellularis with the nucleus ovalis of reptiles. This nucleus superficialis parvocellularis is the same as the nucleus of the septo~mesencephalic tract of EDINGER and WALLENBERG (1899). The name was first used by RENDAHL (1924), who, however, under this term included the nucleus lateralis of EDINGER and WALLENBERG. The nucleus superficialis parvocellularis is a band of gray matter along the lateral aspect of the dorsal thalamus throughout almost the whole of its extent, in which the ramus dorsalis of the septo~mesencephalic tract on its way to the midbrain splits up for a great part (fig. 7). nuc/. il1tet"st. stro te"m. lam. hyp.rs-l:r. 1I med. dors . tr. qv i 111.~fto"t. +sept, mu.r.b.c. nvtl.l'htop.inf. h. infv .. d. neosfr: il1term. + c4 ud.p.3I1t. l1eostr. cdud.p.post. hype.str. ventr. p.d. nvel. dorso!at. ant.p.lat. l1ucl. tr. sepbnes. "'S~+?~~.,,:-'-+-_tr. septoll14S. '" ram. dors. Fig. 7. gri5. het. "vel. g-en . lat. dors. SPARROW. Cross-section approximately through middle of thalamw:. WEIGERT-PAL-paracarmine. X 10. The first argument of HUBER and CROSBY in homologizing the nucleus superficialis parvocellularis of birds with the nucleus ovalis of reptiles is that the position of the two (dorsal to the lateral forebrain bundie and lateral to the nucleus dorsolateralis anterior) is approximately the same. Prom our side, however, it may be stated that the position of the nucleus
1103 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
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 and 8: 1099 by H UBER and CROSBY (their co
Page 9: 1101 that its chief supply is by fi
Page 13 and 14: 1105 lateralis anterior. They faile

The nucleus of BELLONCI in birds - DWC

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?