(* Huxley, ibid. page 29.)
If the muscles, viscera, or any other part of the animal fabric, including the brain, be compared, the results are declared to be similar.
WHETHER THE STRUCTURE OF THE HUMAN BRAIN ENTITLES MAN TO FORM A DISTINCT SUB-CLASS OF THE MAMMALIA.
In consequence of these and many other zoological considerations, the order Bimana had already been declared, in 1856, by Isidore G. St. Hilaire in his history of the science above quoted "to have become obsolete," even though sanctioned by the great names of Blumenbach and Cuvier. But in opposition to the new views Professor Owen announced, the year after the publication of G. St. Hilaire's work, that he had been led by purely anatomical considerations to separate Man from the other Primates and from the mammalia generally as a distinct SUB-CLASS, thus departing farther from the classification of Blumenbach and Cuvier than they had ventured to do from that of Linnaeus.
The proposed innovation was based chiefly on three cerebral characters belonging, it was alleged, exclusively to Man and thus described in the following passages of a memoir communicated to the Linnaean Society in 1857, in which all the mammalia were divided, according to the structure of the brain, into four sub-classes, represented by the kangaroo, the beaver, the ape, and Man respectively:—
"In Man, the brain presents an ascensive step in development, higher and more strongly marked than that by which the preceding sub-class was distinguished from the one below it. Not only do the cerebral hemispheres overlap the olfactory lobes and cerebellum, but they extend in advance of the one and farther back than the other. Their posterior development is so marked that anatomists have assigned to that part the character of a third lobe; it is peculiar to the genus Homo, and equally peculiar is the 'posterior horn of the lateral ventricle' and the 'hippocampus minor' which characterises the hind-lobe of each hemisphere. The superficial grey matter of the cerebrum, through the number and depth of its convolutions, attains its maximum of extent in Man.
"Peculiar mental powers are associated with this highest form of brain, and their consequences wonderfully illustrate the value of the cerebral character; according to my estimate of which I am led to regard the genus Homo as not merely a representative of a distinct order, but of a distinct sub-class of the mammalia, for which I propose the name of 'Archencephala.'"*
(* Owen, "Proceedings of the Linnaean Society" London volume
8 page 20.)
The above definition is accompanied in the same memoir by the following note:—"Not being able to appreciate, or conceive, of the distinction between the psychical phenomena of a chimpanzee and of a Boschisman, or of an Aztec with arrested brain-growth, as being of a nature so essential as to preclude a comparison between them, or as being other than a difference of degree, I cannot shut my eyes to the significance of that all-pervading similitude of structure—every tooth, every bone, strictly homologous—which makes the determination of the difference between Homo and Pithecus the anatomist's difficulty; and therefore, with every respect for the author of the Records of Creation,* I follow Linnaeus and Cuvier in regarding mankind as a legitimate subject of zoological comparison and classification."
(* The late Archbishop of Canterbury, Dr. Sumner.)