226 



Prof. G. E. Smith. On a Peculiarity of the [Mar. 5, 



tures of Lord Kelvin, using a standard microfarad condenser, and 

 employing the electrometer itself as indicator, is # 363 microfarad at 

 the part used in this experiment. 



" On a Peculiarity of the Cerebral Commissures in certain Mar- 

 supialia, not hitherto recognised as a Distinctive Feature of 

 the Diprotodontia." By G-. Elliot Smith, M.D., Ch.M.. 

 Professor of Anatomy, Egyptian Government School of 

 Medicine, Cairo, and Eellow of St. John's College, Cambridge. 

 Communicated by Professor G. B. Howes, F.RS. Eeceived 

 March 5— Eeacl March 20, 1902. 



It has been known for a considerable time that some of the fibres of 

 the ventral commissure of the cerebrum in certain Marsupials dissociate 

 themselves from the rest of the commissure as soon as they have crossed 

 the mesial plane ; and that, instead of passing bodily into the external 

 capsule, which is the usual course of the fibres of the ventral or 

 anterior commissure, they form an aberrant bundle which associates 

 itself with the internal capsule so as to reach the dorsal area of the 

 neopallium by a shorter and slightly less circuitous course (fig. 2). 



This peculiarity was represented in the drawings of sections through 

 the brains of Macropus and Phascolomys, in 1865, by the late W. H. 

 Flower.* It was more distinctly shown in a diagram! illustrating 

 a coronal section through the brain of a Derbian Wallaby which 

 was published 27 years later by Johnson Symington. Two years 

 later I placed on record the observation upon it, that " in Phalangista 

 [Trichosurus vulpecula] a bundle of anterior commissure fibres proceeds to 

 the cortex via the internal capsule, in addition to the external cap- 

 sule,"! and in the same place noted an analogous arrangement in 

 various species of Macropus. 



In 1897 Theodor Ziehen recorded§ the presence of such fibres in 

 Macropus, Aepyprymnus, and Phascolarctus ; but, like Flower and Syming- 

 ton before him, he did not venture on any explanation of them. 



* " On the Commissures of the Cerebral Hemispheres of the Marsupialia and 

 Monotremata, as compared with those of the Placental Mammals," 'Phil. Trans.,' 

 vol. 155 (1865), p. 633. 



f " The Cerebral Commissures in the Marsupialia and Monotremata," ' Journal 

 of Anatomy and Physiology,' vol. 27, 1892, fig. 3, p. 81. 



X " Preliminary Observations on the Cerebral Commissures," ' Proc. Linn. Soc. 

 of N.S.W.,' 1894, pp. 647—648. 



§ "Das Centralnerven system d. Mono tremen und Marsupialia (Semon's Zoolo- 

 2,-ische Forschungs-Reisen in Australien)," ' Denkschr. Medic. -naturwis. G-esellsch. 

 Jena,' vol. 6, Lf. II and IV, 1897—1901. 



