52 
REVIEWS. 
The chief peculiarities in most modem systems have reference to the 
position which the Marsupial and Monotrematous mammals occupy. 
The parallelism between the subdivisions of the Marsupialia with the 
several orders of the placental mammals would seem to have more espe¬ 
cially attracted the attention of the Trench naturalists. Greofiroy St. 
Hilaire went so far as to raise the former to the rank of a distinct class. 
The arrangement of the Mammalia by the late Prince C. Lucien Buona¬ 
parte, according to developmental and generative characters, and his 
subdivision of the Placentalia into the two groups of Educabilia and 
Ineducabilia, is regarded by Professor Owen as “ the most important 
improvement in the classification of the Mammalia which has been pro¬ 
posed since the establishment of the natural character of the Implacental 
or 0voviviparous division.” 
After mature deliberation, Professor Owen comes to the conclusion, 
that all the systems which have hitherto been proposed for the classifi¬ 
cation of the Mammalia are more or less liable to objection. He accord¬ 
ingly proceeds to give an explanation of his own views on the subject. 
These are based on the four leading modifications of cerebral structure 
which the Mammalia present. 
“ The brain is that part of the organization which, by its superior development, dis¬ 
tinguishes the Mammalia from all the inferior classes of Vertebrata; and it is that organ, 
which I now propose to show to be the one that, by its modifications, marks the best 
and most material primary divisions of the class. 
“ In some mammals the cerebral hemispheres are but feebly and partially connected 
together by the ‘ fornix’ and ‘anterior commissurein the rest of the class a part called 
‘ corpus callosum’ is added, which completes the connecting or ‘ commissural ap¬ 
paratus.’ 
“ With the absence of this great superadded commissure is associated a remarkable 
modification of the mode of development of the offspring, which involves many other mo¬ 
difications ; amongst which are the presence of the bones called ‘ marsupial,’ and the 
non-development of the deciduous body concerned in the nourishment of the progeny 
before birth, called ‘ placenta;’ the young in all this ‘ implacental’ division being 
brought forth prematurely, as compared with the rest of the class. This first and lowest 
primary group, or sub-class, of Mammalia may be termed, from its cerebral character, 
Lyencephala,—signifying the comparatively loose or disconnected state of the cerebral 
hemispheres. The size of these hemispheres is such that they leave exposed the olfactory 
ganglions, the cerebellum, and more or less of the optic lobes 5 their surface is generally 
smooth ; the anfractuosities, when present, are few and simple. 
“ The next well-marked stage in the development of the brain is where the corpus 
callosum is present, but connects cerebral hemispheres as little advanced in bulk or out¬ 
ward character as in the preceding sub-class; the cerebrum leaving both the olfactory 
lobes and cerebellum exposed, and being commonly smooth, or with few and simple con¬ 
volutions in a very small proportion, composed of the largest members of the group. 
The mammals so characterized constitute the sub-class Lissencephala. 
“The third leading modification of the mammalian cerebrum is such an increase in 
its relative size, that it extends over more or less of the cerebellum; and generally more 
or less over the olfactory lobes, save in very few exceptions, cases of the smaller and in¬ 
ferior forms of Quadrumana , the superficies is folded into more or less numerous gyri or 
convolutions, whence the name Gyrencephala, which I propose for the third sub-class of 
Mammalia. 
“ 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 cere- 
