ELECTRICAL FISHES 



403 



basilare, a seemingly unpaired grayish bundle of nerves (Fig. 262, 

 ne) appears from below, apparently from the lower (anterior) 

 median cleft. This bundle at once divides right and left, and 

 consists of three pairs of nerves, closely invested with connective 

 tissue, the roots of the second and third spinal nerves, and the elec- 

 trical nerve. Bilharz regarded the last as a new element, inserted 

 between the others, while Fritsch (12) has 

 determined its connection with the so - called 

 lateral nervous system, derived in all fishes from 

 the trigeminus and vagus. The physiological 

 function of this system is to supply the skin- 

 organ, which is so highly developed in fishes, 

 with secretory and sensory nerve-fibres. The 

 superficial portion of the lateral nervous system 

 of the vagus in Malapterurus, as shown by 

 Fritsch, runs over the electrical nerve just beneath 

 the shoulder-girdle, and then posteriorly into the 

 muscles. Comparative observations on the 

 lateral nervous system of the closely allied, non- 

 electrical, common cat-fish (Silurus) shows that 

 the truncus lateralis vagi emerges after interlacing 

 with the lateralis trigemini " in two fasciculi 

 behind the shoulder-girdle. Immediately after 

 its passage it sends a slender branch to the skin 

 for the shoulder region, and a stronger descend- 

 ing branch to the anterior extremities, and their 

 vicinity, and to the skin of the ventral region. 

 A superficial branch is then given off, which 

 passes downwards from the lateral canal in the antero-posterior 

 direction, and sends 56 long descending branches to the ventral 

 region just below the skin." All these branches of the truncus 

 lateralis are wanting in Malapterurus, being replaced (in Fritsch's 

 opinion) by the electrical nerve, which here represents a branch of the 

 nerve that in other fishes subserves secretory and sensory functions. 



And, in fact, like the lateralis vagi in the. cat-fish, this nerve 

 does, immediately after its exit from the vertebral column, send 

 out a fine ramus to the shoulder region, and pectoral fin, which 

 reappears at the inner border of the head of the lateral 

 muscle to the shoulder -girdle, along with the artery of the 

 electrical organ. It then passes backwards between this and the 



FIG. 262. 



