276 ANNUAL OF SCIENTIFIC DISCOVERT. 



and life's forms, going on somewhere in the far recesses of Na- 

 ture's womb ? " 



THE BRAIN OF THE IMTLACENTAL MAMMALIA. 



In a paper published in the "Proceedings of the Royal Society," 

 by Mr. W. II. Flower, "On the Commissures of the Cerebral 

 Hemispheres of the Marsupialia and Monotremata," is given the 

 progress of cerebral anatomy, arising from the controversies of 

 the last few j-ears. It also demonstrates that all tliose animals 

 which agree in the physiological character of su<;kling their 

 young, and are separated therel)y from every other creature, also 

 agree in possessing the remarkable transverse band of fibres 

 which connects the two hemispheres of the brain, and is called 

 the corpus callosum, while neither bird, reptile, amphibia, nor 

 fish, have hitherto disclosed a trace of that structure. 



Tims the progress of cerebral anatomy, while it has destroyed 

 the distinctions feigned to exist between man and the speechless 

 hii^hcr mammals, has also annihilated the I'csemblances imagined 

 to Obtain between the lowest mammals and the ovipara. 



At the outset, a confirmation is aftorded of the imi)ortant fact, 

 first observed l»y Prof. Owen, that the brains of animals of the 

 orders marsui)ialia and monotremata present certain special and 

 peculiar characters, by which they may be at once distinguished 

 from those of other mammals. The appearance of either a trans- 

 verse or longitudinal section would leave no doubt whatever as 

 to which group the In-ain belonged. In the differentiating char- 

 acters to be enumerated, some members of the higher section 

 present an approximation to the lower ; but, as far as is known at 

 present, there is still a wide interval between them, without any 

 connecting link. 



The differences are manifold, but all have a certain relation to, 

 and even a partial dependence on, each other. They may be 

 enumerated under the following heads: — 



1. The peculiar arrangement of the folding of the inner wall 

 of the cerebral hemisphere. A deep fissure, with corresponding 

 projection within, is continued forwards from the hippocampal 

 fissure, almost the whole length of the inner wall. 



2. The altered relation (consequent upon this disposition of the 

 inner wall) and the very small development of the upper trans- 

 verse commissural fibres (corpus callosum). " 



3. The immense increase in amount, and pi'obably in function, 

 of the inferior set of transvei'se commissural fibres (anterior com- 

 missure) . 



But is not the main part of the " corpus callosum" of the pla- 

 cental mammals also reiiresented by the upper and the anterior 

 part of the transvei'se band which passes between the hemispheres 

 of the mai'supial brain, and radiates out in a delicate lamina above 

 the anterior part of the lateral ventricle ? The most important 

 and, indeed, crucial test, in determining this question, is, its posi- 

 tion in regard to the septum ventviculorum, and especially the 

 precommissural fibres of the fornix. Without any doubt, iu all 



