1881.] Comparative Structure of the Brain in Rodents. 15 



Average excess in favour of direct transmission. 





Degrees of 



Thermometric 





galvanometer. 



values. 



At the end of 2 minutes 



6 -536° 



-004402° C. 



When permanent thermal con- 









20 -470 



-013804 



Unfortunately the tissues with which we are dealing obey no phv- 

 sical law with which the writer is acquainted, as regards the effect of 

 changes of thickness of the conductor. It is, therefore, impossible to 

 reason with accuracy from one thickness to another. The effect of 

 the circulation of the blood in the head on the outward transmission 

 of heat from the brain, has been somewhat fully considered by the 

 writer elsewhere.* 



VI. " On the Comparative Structure of the Brain in Rodents." 

 By W. Bevan Lewis, L.R.C.P. (Lond.), Senior Assistant 

 Medical Officer to the West Riding Asylum, Wakefield. 

 Communicated by Dr. Ferrier, F.R.S., Professor of Forensic 

 Medicine, Kings College, London. Received October 13, 

 1881. 



(Abstract.) 



I have endeavoured in this abstract to summarise the results of my 

 recent researches into the minute structure of the brain in the smaller 

 Rodents. The pig and sheep, which were the subjects of my former 

 memoir, possess a highly developed olfactory apparatus conjoined to 

 a well convoluted cortical surface ; but in the smaller animals now 

 under consideration the surface of the hemispheres is almost per- 

 fectly smooth, while the olfactory organ, from its comparative size 

 and complex relationship, has an important part to play in the archi- 

 tecture of the brain. 



Animals possessing the latter type of cerebrum have been classed 

 together as the Osmatic Lissencephales, in contradistinction to those 

 which were the subject of my former enquiries, the Osmatic Gyren- 

 cephales. My researches into the structure of the brain of prominent 

 members of the former group, viz., the rabbit and rat, may be con- 

 sidered under two heads : — 



(a.) The histology of the complete cortical envelope. 



* " Kegional Temperature of the Head." London, 1879. 



