io6 LIFE OF FLOWER 



large mass of transverse white fibres called 'corpus 

 callosum' by the anthropotomist ; which fibres, over- 

 arching the ventricles and diverging as they penetrate 

 the substance of either hemisphere of the cerebrum, 

 bring every convolution of the one into communication 

 with those of the other hemisphere, whence the other 

 name of this part the ' great commissure.' In that 

 year I discovered that the brain of the kangaroo, the 

 wombat, and some other marsupial quadrupeds, wanted 

 the ' great commissure ' ; and that the cerebral hemi- 

 spheres were connected together, as in birds, only by 

 the { fornix ' and ' anterior commissure.' Soon afterward 

 I had the opportunity of determining that the same 

 deficiency of structure prevailed in the Ornithorhynchus 

 (duckbill) and Echidna (spiny ant-eater)." 



Owen's conclusions with regard to the absence of the 

 great connecting band of fibres between the hemispheres 

 of the marsupial brain were first published in the Philo- 

 sophical Transactions for 1837 ; those, with regard to the 

 same lack in the monotremes, being added in Todd's 

 Cyclopedia of Anatomy and Physiology, Article " Mono- 

 tremata." In the latter article it was also stated that 

 the brain of the echidna was further distinguished from 

 that of other mammals by the circumstance that whereas 

 in the latter the portion of the brain known as the optic 

 lobes consists of four lobes (corpora quadrigemina), in 

 the echidna and duckbill there are only a pair of such 

 lobes (corpora bigemina.) 



In consequence of this supposed lack of the corpus 

 callosum in their brains, Owen separated the marsupials 

 and monotremes from other mammals in a primary group 

 by themselves, under the title of Lyencephala. 



