XXXI.] 



CEREBRUM. 



357 



layer already described. If the cerebellar lamina be cut in a direction trans- 

 verse to the course of these fibres, then they merely appear as black dots. 

 My experience leads me to believe that this system is best demonstrated by 

 the rapid Gclgi method. 



11. Cerebrum by Golgi's Method (see Lesson XXX. 19). Do the same as 

 for the cord and cerebellum. Either the AgN0 3 or HgCl. 2 methods may be 

 adopted. In the latter case the best results are obtained by keeping the por- 

 tions of the brain for months in the mercuric-chloride 



solution. I have usually got good results with the 

 brain of the rat or rabbit. In all cases mount the sec- 

 tions in balsam without a cover-glass. In new-born 

 animals better results are obtained especially with the 

 rapid method (osmico-bichromate method, p. 345) than 

 with adult brains. Fig. 331 shows some of the results 

 which may be obtained in a T. S. of the brain of a new- 

 born rat. The results have been pieced together from 

 a study of many sections. 



By the rapid Golgi method it is easy to obtain beauti- 

 ful preparations showing the pyramidal cells of the 

 cortex with their apical, lateral, and axis-cylinder pro- 

 cesses ; in fact, I have often obtained such in the 

 superficial sections after a few hours' immersion in 

 silver n itrate. For the cornu ammonis cells the double- 

 impregnation method of K. y Cayal is excellent. Some- 

 times, however, one gets the blood-vessels stained. 



12. Cerebrum by Weigert or Weigert-Pal's Method 

 (see Lesson XXX. 4). This method reveals the exist- 

 ence of medullated fibres in the cerebral cortex arranged 

 according to the scheme shown in fig. 332. 



-At the lower part of the grey matter a large number 

 of fine medullated nerve-fibres enter it radii which 

 run outwards in the cortex as medullary rays. Between 

 the latter is an inter-radial plexus, and above them is 

 a supra-radial plexus, and quite under the pia are tan- F 

 gential fibres. On the boundary-line between the supra- 

 radial plexus and the inter-radial plexus is a white 

 stripe, visible to the naked eye, especially well marked 

 in the cuneus. It has been called the stripe of Genuari, 

 Baillarger, and also of Vico d'Azyr. 



13. Medullated Nerve-Fibres in the Cortex Cerebri. 

 Place very small pieces of the outer part of the cortex 

 in i per cent, osmic acid (24 hours). The pieces must 

 be black throughout. Make thin sections, place one 

 on a slide, add a drop of ammonia ; the section swells 

 up and the medullated fibres become distinct. Expose 

 the section to the vapour of osmic acid, i.e., place the 

 section on a slide over a glass thimble filled with osmic 



acid and cover the whole with a bell-jar. After half an hour or less the 

 "fixation" is complete. This is Exner's method as modified by Ranvier. 

 Preserve in glycerine. Observe the narrow medullated nerve-fibres between 

 the nerve- cells"; the nuclei only of the latter are distinctly seen. 



Hypophysis Cerebri or Pituitary Body. 



14. Hypophysis Cerebri. This consists of two parts, the one derived from 

 the brain, a continuation of the infundibulum ; the lower part is derived from 



332. V.S. Cortex 

 Cerebri. The right 

 side drawii from a 

 Weigert's lijema- 

 toxylin preparation, 

 and the left from a 

 Golgi's sublimate 

 one. On the ri^ht 

 the mednllated 



fibres, and on the 

 left only the nerve- 

 cells are shown. 

 There are really 

 more cells than 

 shown in the draw- 

 ing. 



