1865.] Paper " on Zoological Names" %c. 137 



bridge in 1859 * (p. 23) : "At length, having dissected the brain, in one 

 species at least, of almost every genus or natural family of the mammalian 

 class, I felt myself in a position to submit to the judgment of my fellow la- 

 bourers in Zoology, at the Linnean Society in 1857, the generalized results 

 of such dissections, comprising a fourfold primary division of the MAM- 

 MALIA based upon the four leading modifications of cerebral structure in 

 that class. 



" In some mammals the cerebral hemispheres are but feebly and partially 

 connected together by the ' fornix ' and ' anterior commissure ' ; in the rest 

 of the class the part called * corpus callosum ' is added, which completes 

 the connecting or ' commissure ' apparatus. 



" With the absence of this great superadded commissure is associated a 

 remarkable modification of the mode of development of the offspring. * * * 

 This first and lowest primary group, or subclass of Mammalia, is termed, 

 from its cerebral character, LYENCEPHALA, signifying the comparatively 

 loose or disconnected state of the cerebral hemispheres." 



I think that I should scarcely be blamed for putting my trust in an au- 

 thor's own description of the " generalized results " of his researches, deli- 

 berately laid before his fellow-labourers at a meeting of a learned Society 

 twenty years after those researches were made. 



I may add, moreover, that the works, both English and foreign, upon 

 Comparative Anatomy and Physiology, in which the simple fact that the 

 marsupials and monotremes differ from the other mammalia by the absence 

 of a corpus callosum or great transverse commissure to their brain is 

 stated upon the authority of Prof. Owen, may be said to comprehend 

 most of those of any importance published since the year 1837. One or 

 two examples will suffice. MM. Eydoux and Laurent (Voyage de la Fa- 

 vorite) have thrown into a tabular form the published results of the dis- 

 sections of the brains of the Implacental Mammalia as compared with pla- 

 cental mammals and birds, in which Table the part played by the corpus 

 callosum is as follows : 



IMONODELPHKS. I DlDELPHES. I ORNITHODELPHES. I OlSEAUX. 

 existe. | manque. | manque. | manque." 



This statement of the " resultat des observations de M. R. Owen," so far 

 from having called forth the strictures of that anatomist, is quoted with 

 approbation in his article " Monotremata" in the ' Cyclopaedia of Anatomy 

 and Physiology.' 



In Van der Hoeven's ' Zoology,' vol. ii. p. 596 (Dr. Clark's edition), it 

 is stated that " the great transverse commissure of the hemispheres of the 

 cerebrum is, with the exception of the Monotremes and Marsupiates 

 (R. Owen, 'On the Structure of the Brain in Marsupial Animals,' Phil. 

 Trans. 1837), present in all mammals." In the preface of the same work, 

 the editor, speaking upon the authority of the above-mentioned paper in 

 the Journal of the Linnean Society, says, " In some mammals the cerebral 

 * On the Classification and Geographical Distribution of the Mammalia, 1859. 



