228 Journal of Comparative Neurology. 



spinals turn ventrad, along the outer face of the mner 

 lamella of the cleithrum. In the latter nerve the fibres 

 from the two sources cannot be separately followed, but 

 all enter the ventral portion of the levator of the pectoral 

 fin {lev.) The sensory fibres last mentioned (/. d. 2) pass 

 to the pectoral fin and break up into several ramuli which 

 run out parallel with the fin rays, thus supplying the skin 

 of the dorsal part of the fin, i. ^., the portion not inner- 

 vated by the third spinal. 



On the right side of the specimen upon which this de- 

 scription is based the composition of the brachial plexus is 

 in one respect different. The middle portion of the pec- 

 toral fin is supplied by a nerve which has the same course 

 over the depressor of the fin as the corresponding nerve 

 on the left side, but which has a double origin. The 

 greater portion of the fibres arise from the mixed ventral 

 rami of the first and second spinals before that nerve has 

 pierced the scapula; they can be traced back to the dorsal 

 root of the second spinal nerve. Shortly after their sepa- 

 ration these fibres are joined by a much smaller twig from 

 the third spinal, which arises at a point corresponding to 

 the origin of the main nerve on the opposite side and then, 

 instead of going caudad to the fin, turns cephalad for a 

 considerable distance to effect the anastomosis. Which 

 of these two cases is to be regarded as typical for this 

 species, it is impossible to state, as comparative data are 

 lacking. 



IV. — The First Spinal Nerve. 



The first spinal nerve (Fig. 7) differs widely from the 

 others and shows very plainly that it is formed by the in- 

 complete fusion of at least two segmental nerves. There 

 are four roots, two dorsal and two ventral, all well devel- 

 oped and the two pairs widely separated. It is obvious 



