370 



SPECIAL HISTOLOGY. 



Tig. 145. 



to do so by weighty reasons, and much regretting that I am unable to 

 maintain a view, which appeared to throw so much light upon many diffi- 

 cult parts of the physiology of the nerves, and to be in accordance with 

 so many other anatomical conditions (ganglia, invertebrate animals). 



Volkmann, in his hypothesis of the origination of the fibres in the 

 cord, relies upon the circumstance (1. c, p. 482, et seq.), that the spinal 

 cord is not of a pyramidal form with the base above, as must have been 

 the case had all the fibres of the roots of the nerves ascended towards 

 the cerebrum, but that it rather presents a local increase of the nervous 

 substance at the points of origin of large nerves, which enlargement is 

 not confined to the gray substance, but equally involves the white. That 

 this is the case Volkmann shows from four transverse sections of the 

 spinal cord of the Horse, and from a comparison of the diameter of the 

 cervical cord of Crotalus horridus, with that of all the nerve-roots of 

 the same animal, which was found to be eleven times greater than the 

 former. He also supports his view by the consideration : 1, that the 

 enlargements of the cord are always regulated by the size of the nerves 

 of the extremities, being sometimes wanting and sometimes enormously 

 developed ; 2, that the cord, at the points of exit of the largest nerves, 

 instead of becoming suddenly thinner, is in most cases 

 enlarged ; and 3, that the origin of the spinal acces- 

 sory nerve in this case loses all that is remarkable in it. 

 Now, if the spinal cord in man be examined with refe- 

 rence to the above points, it will present, in almost all 

 of them, exactly the contrary of what Volkmann noticed 

 in animals. In the first place, the ivTiite substance con- 

 stantly increases in tJiicTcness from helotv upwards, and 

 the enlargements of the cord depend upon an increase of 

 the gray substance more than anything else. That this is 

 the case, is evident at a glance, when sections, such as are 

 represented, after nature, in Fig. 145, are compared with 

 each other, and it also admits of being estimated in 

 numbers {vid. " Mikroskop. Anatomic," II. 1, p. 431). 



This fact being established, it remains to determine 



the proportion borne by the white substance in the 



superior cervical region to the peripheral nerves. For 



this purpose I instituted Volkmann's measurements in 



man, and in a male and female 'cody estimated all the roots of the spinal 



nerves on the left side; I determined, from the ascertained diameters, 



Fig. 145. — Five transverse sections through ^ human spinal cord, hardened by chromic 

 acid, to show the relative proportions of the gray and white substances, — of the natural size : 

 Jt, from the conus medullaris, the diameter of the cord being 3| lines ; J5, from the lumbar 

 enlargement, transverse diameter 4| lines, antero-postenor 4| lines; C, from the dorsal part 

 of the cord, 4:1 and 3f lines ; D, from the cervical enlargement, G| and 4| lines ; E, from 

 the superior cervical portion, level with the second nerve, 6| and 4| lines. 



