460 



of an expedition which he made with a view to investigate the cir- 

 cumstances of this remarkable meteorological phenomenon, and 

 proposes a theory for its explanation. 



" A Meteorological Journal kept at Allenheads, 1400 feet above 

 the level of the Sea, from the 1st of May to the 1st of November, 

 1836." By the Rev. William Walton. Communicated by P. M. Ro- 

 get, M.D., Sec. R.S. 



January 26, 1837. 



FRANCIS BAILY, Esq., V.P. and Treasurer, in the Chair. 

 A paper was read, " On the Structure of the Brain in Marsupial 

 Animals." By Richard Owen, Esq., F.R.S., Hunterian Professor of 

 Anatomy to the Royal College of Surgeons. 



The author describes a remarkable modification in the commis- 

 sural apparatus, apparently provided with a view to establish com- 

 munications between the cerebral hemispheres, which he has ob- 

 served in the brains of marsupial animals, and which has hitherto 

 been regarded as constituting the essential difference between the 

 brains of oviparous and mammiferous vertebrata, but which he con- 

 siders as indicating a certain relation between the greater perfection 

 of that organ, resulting from the superior magnitude of the great 

 commissure, or corpus callosum, and the placental mode of deve- 

 lopement in the true mammalia. In a former paper he adduced evi- 

 dence tending to show that both a small developement of the cere- 

 bral organ, and an inferiority of intelligence are the circumstances 

 in the habits and structure of this singular tribe of animals most con- 

 stantly associated with the peculiarities of their generative economy: 

 and the repeated dissections he has since made, an account of which 

 is given in the present paper, have afforded him the most satisfactory 

 confirmation of this coincidence, between a brief intra-uterine ex- 

 istence, together with the absence of a placental connexion between 

 the mother and the foetus, and an inferior degree of cerebral de- 

 velopement. Thus, on comparing the structure of the brain in the 

 Beaver and in the Wombat, he finds that the corpus callosum, or 

 great commissure which unites the supraventri- cular masses of the 

 hemispheres in the former, as well as in all other placentally deve- 

 loped mammalia, and which exists in addition to the fornix, or 

 hippocampal commissure, is wholly absent in the latter animal : 

 and that a similar deficiency exists in the brain of the Great and 

 Bush Kangaroos, of the Vulpine Phalanger, of the Ursine and 

 Mange's Dasyurus, and of the Virginian Opossum ) whence he 

 infers that it is probably the characteristic feature of the structure 

 of the marsupial division of mammalia. In this modification of the 

 commissural apparatus, the Marsupiata present a structure of brain 

 which is intermediate between that of the Placental Mammalia and 

 Birds ; and hence the Marsupiata, together with the Monotremata, 

 may be regarded as constituting a distinct and peculiar group in the 

 former of these classes, although they include forms, which typify 

 the different orders of the ordinary Mammalia. 



