1890.] On the Cingulum, fyc., of the Maiinoset Monkey. 271 



the lower ends from the inside by the breadth of the hook. If now 

 the distances between the fibres top and bottom are nearly the same, 

 no sensible error will be made by taking the product of these distances 

 as equal to the product of the breadth of the hook and the width of 

 the metal aperture. (2.) To render the controlling couple produced 

 by the deflected bifilars independent of temperature, it is proposed to 

 select metals with appropriate coefficients of expansion for regulating 

 the dimensions of the bitilars top and bottom, and to alter the length 

 of the silk fibres by an appropriate arrangement, so that a pointer 

 attached to the hook at the lower end shall always come to a fiducial 

 point upon a strip of brass attached to the metal framework which 

 forms the upper suspension. The neatest way of doing this seems to 

 be to cement the plane and silvered side of a short-focus plano-convex 

 lens to the strip of brass, and to arrange its position with reference 

 to the pointer so that the tip of the latter is exactly in the focus of 

 the lens. In this position the tip and its reflected image will appear 

 just in coincidence, and if necessary a lens may be provided in the 

 side of the instrument for observing the relative positions of the 

 pointer and its image and adjusting them to coincidence.] 



VIII. " On the course of the Fibres of the Cingulum and the 

 Posterior Parts of the Corpus Callosum and of the Fornix 

 in the Marmoset Monkey." By Charles E. BEEVOK, M.D., 

 F.R.C.P. Communicated by Professor FERRIEB, F.R.S. 

 Received June 12, 1890. 



(Abstract.) 



This paper has for its scope the investigation by the microscope of 

 the coarse of certain fibre-tracts iu the brain which have not 

 hitherto been minutely examined. 



After an introduction showing the difficulties of tracing these 

 fibres by dissection and by pther means, the method of investigation is 

 given. This consisted in cutting serial sections of the brain of the 

 Marmoset Monkey (Hapale jactans and penicillata) after hardening 

 in bichromate of potash ; the sections were stained by Weigert's and 

 also by Pal's haematoxylin methods, whereby the fibres are differenti- 

 ated. In this way, a complete series of sections was made in the 

 sagittal and horizontal planes, and almost a complete series in the 

 frontal direction, and by combining the appearances found in the 

 three planes, a mental picture of the whole could thus be obtained. 



In the description of this brain, emphasis is laid on its small size, 

 which renders it very easy of manipulation, while, from its high 

 position in the animal scale, its general arrangement is comparable 



