Mason — Central Nervous System of Reptiles^ etc. 7 



the brachial enlargement, many fibres from the inferior roots 

 enter the cord at right angles, and remain in the same vertical 

 plane while describing a curve laterall}^ the convexity of which 

 lies towards the inferior median fissure. This is why longitu- 

 dinal sections are useless for showing this connection; while 

 a series of transverse sections, made in the section cutter, in- 

 cluding the roots of the second pair of nerves, will often 

 show, in well stained specimens, the greater ])ortion, if not 

 all, the root fibres passing through the white substance, and, 

 after entering the grey substance, branchino: outwards amono: 

 the cells. Most of the fibres lose themselves among the larger 

 external group of cells, while a few are seen to unite with the 

 upper group. In several instances I have traced a connection 

 between cell process and nerve-fibre, with so much certainty, 

 confirming the observation by using a binocular instrument, 

 that I am forced to believe not only in the possibility, but the 

 facility of demonstrating in this way an important fact. 



It is always advisable to submit the transparent section to 

 microscopic examination before it is covered, as the weight of 

 the cover is often sufficient to sever fibres. Good objectives, 

 of considerable power, can be used in studying uncovered 

 preparations ; and I have succeeded in obtaining satisfactory 

 photographs of some of these. 



CONCLUSIONS. 



1. The central canal of the spinal cord of frogs is more 

 nearly cylindrical in shape than has been generally supposed. 

 The oval contour is not seen in cross sections below the 

 second pair of nerves, when the membranes are not removed 

 before hardening. 



2. The nuclei of the large nerve-cells are more generally 

 oval in form than are those of the smaller cells. I have con- 

 firmed this in a few fresh preparations only. It is possible 

 that the re-agents employed have a different effect upon the 

 two classes of nuclei, but it seems more reasonable to con- 

 clude that they have a different form anatomically. 



3. The nerve-cells of the crural enlargement are as abundant 

 as those of the brachial enlargement, if not more so. Their 

 nuclei are larger, as are also the surrounding masses of pro- 

 toplasm or cell bodies. 



