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XIY. On the Comparative Structure of the Brain in Rodents. 
By W. Bey an Lewis, L.R.C.P. (Bond.), Senior Assistant Medical Officer, 
West Riding Asylum, Wakefield. 
Communicated by Dr. Ferrier, F.R.S. 
Received October 13, — Read November 17, 1881. 
[Plates 49, 50.] 
In a former memoir published in the Philosophical Transactions' 1 ' I have detailed the 
result of researches into the minute anatomy of the cortex cerebri in the Pig as contrasted 
with that of the Sheep, the Cat, and other animals. In continuation of the same 
series of researches it is proposed to consider here the results obtained by a still more 
extended enquiry into the structure of the brain in the Bodentia, and with this object 
in view, I shall divide my subject into the two lines of investigation followed out :— 
first, the histology of the entire cortical envelope, and secondly, the central projections of 
the olfactory organ. It is necessary that such an account be preceded by a short 
sketch of the external conformation of the brain in Bodents, and that its topography 
should be mapped out under the more recent and accurate nomendature introduced 
by the late Professor Broca, whose work upon the comparative anatomy of the 
convolutions in Mammalian brainst is by far the most philosophical and trustworthy 
treatise which has appeared on this subject since the publications of Turner, | Bischoff,§ 
and Ecker.II Since the cerebrum of the Babbit affords the type for the brain of the 
Bodent, and since this animal, together with the Bat, was chiefly utilised in these 
investigations, my sketch will be limited to the brains of these two animals. 
External Conformation of Brain in the Bat and Babbit. 
When investigating the structure of the brain in the Pig and Sheep I had to deal 
with a highly developed olfactory apparatus, associated with a richly convoluted 
* “ Researches on the Comparative Structure of the Cortex Cerebri,” Pbil. Trans., Part I., 1880. 
t “ Anatomie Comparee des Circonvolutions,” par M. Paul Broca. Revue d’Anthropologie. 
+ “ Convolutions of the Human Cerebrum Topographically considered.” W. Turner, Edin. Med. 
Journ., 1866. 
§ “ Die Grosshirnwindungen des Menschen.” Dr. Th. L. W. Bischoff. Miinchen, 1868. 
|| “ The Convolutions of the Human Brain.” Dr. Alex. Ecker, Translated by J. C. Gallon. 
