362 



ELECTRO-PHYSIOLOGY 



CHAP. 



the central nervous system. This is no less strongly marked at 

 the origin of the " electrical nerves," which arise from two special 



lobes of the brain, that are wanting in 

 all other fishes. Lorenzini, 1677 (as 

 was pointed out by Boll, 5 cT), described 

 these parts as a posterior pair of 

 tubercles, without divining their function, 

 while A. v. Humboldt was the first to 

 recognise them more exactly for the 

 centres of the electrical nerves of 

 Torpedo. After exposing the central 

 organ, they are perceived as two long 

 grayish-yellow bodies lying close to- 

 gether, from which four nerve -trunks 

 run out right and left, on either side, 

 and supply the organs. According to 

 Fritsch (whose view was also adopted 

 by Schenk on developmental grounds), 

 the dorsally protruding electrical lobes 

 arise from branches of the motor nuclei 

 FIG. 23i.-Mar g inai portion of three of the vagus, in the medulla oblongata, 

 electrical plates: longitudinal w hich, from the excessive proliferation 



aspect of the column. (Ranvier.) 



of the ganglion-cells that subserve a 



special function, appear to be pressed upwards from their original 

 seat on the floor of the fourth ventricle. Transverse sections 

 reveal a dense layer of large ganglion-cells, the axis-cylinder pro- 

 cesses of which pass directly into the fibres of the electrical nerves. 



The character and distribution of the nerves that enter the 

 organ within each single column, or prism, is highly characteristic. 

 As Eudolf Wagner (35) first showed, the fibres all divide up 

 suddenly into many branches before they enter the plates, 

 forming the characteristic bundle (Wagner's brush Figs. 230 

 and 232), of which the spatial distribution, and relations to the 

 single plates, were determined more exactly at a later period by 

 A. Ewald and Fritsch (9). 



They found that the fibres of a brush, about eighteen in 

 number, are superposed upon one another in regular arrangement, 

 entering by the corners of the hexagonal plates ; so that each plate 

 is supplied by six fibres, which again present a rich dichotomous 

 ramification (Fig. 230). 



