THE SPINAL NERVES. 77 



clear, from the ventral ramus c) separates dorsally to enter 

 the depressor of the fin (Fig. 7, i/e/>.) and just before this 

 point the so-called hypoglossus nerve (the r. cervicalis^ 

 Fiirbringer, r. cerv.) separates from the first spinal. This 

 nerve draws off all of the sensory fibres of the r. ventralis 

 b and a smaller number of motor fibres from the same 

 source. It turns directly ventrad from its point of origin, 

 running- down in the walls of the abdominal cavity in the 

 manner typical for ventral spinal rami. It descends first 

 along the caudal face of the m. pharyngo-branchialis ex- 

 ternus, then lower down in the same relation to the m. 

 pharyngo-branchialis internus. Midway of this course 

 two or three minute twigs of fine fibres are given off 

 which run in a lateral direction along the caudal face 

 of the m. pharyngo-branchialis externus to the skin which 

 covers the cleithrum laterally. Having reached the 

 cleithrum, the remaining fibres of the r. cervicalis turn 

 cephalad along the inner surface of the m. pharyngo- 

 branchialis at its origin from that bone. The origin of the 

 pre-zonal ventral musculature from the cleithrum inter- 

 digitates with that of the pharyngo-branchialis, and the r. 

 cervicalis, following the inner border of the latter muscle, 

 comes to lie embedded between two slips of ventral mus- 

 calature (m. sterno-h3^oideus). Here a fine fibred cuta- 

 neous twig is given off ventrally to supply the skin of the 

 ventral surface under the united tips of the two cleithra; 

 the coarser motor fibres (Fig. 3, in. shy.) ramify through 

 the substance of the sterno-hyoideus, which they inner- 

 vate. No fibres from this nerve enter either of the 

 pharyngo-branchial muscles, nor is there any anastomosis 

 with the vagus, though the former condition is said 

 to prevail in Amiurus (Wright, '84) and in the lower 

 fishes (Fiirbringer, '97) and the latter is figured by 



