THE SPINAL NERVES, 83 



VI. — Summary of the Spinal Nerves. 



The typical spinal nerve gives off a ventral ramus, a 

 medial ramus and two dorsal rami. The ventral ramus 

 contains motor and sensory fibres for the ventral muscu- 

 lature and skin. The ramus medius contains motor fibres 

 for the dorsal musculature and cutaneous fibres for the 

 skin in the vicinity of the lateral line canal. This nerve 

 is in no sense comparable with the lateral line branches 

 of the cranial nerves, and the term ramus lateralis would 

 better be avoided in the case of the spinal nerves, as sug- 

 gesting bad morphology. Of the two dorsal rami, the 

 first (r. communicans) is sensory, the second (r. spinosus) 

 is motor. Each r. spinosus anastomoses with the next 

 following r. communicans and supplies the dorsal muscu- 

 lature near the median line, especially the interspinal mus- 

 cles. The r. communicans joins the r. lateralis accessorius 

 and doubtless innervates the overlying skin of the back. 



The brachial plexus receives elements from both por- 

 tions b and c of the first spinal nerve and from the second 

 and third spinals. The pre-zonal portion of this plexus — 

 the ramus cervicalis of Fiirbringer — receives some of the 

 motor fibres of the r. ventralis b and all of the sensory 

 fibres of that ramus. The post-zonal plexus has a single 

 ventral ramus (in the strict sense, i. e., for ventral muscu- 

 lature and skin) which receives some of the sensory fibres 

 from the ventral ramus of the third spinal nerve, all of 

 the motor fibres of that ramus and a small number of 

 motor fibres from the ventral ramus of the second spinal. 

 The sensory ramus for the skin of the side of the body 

 between the pectoral fin and the opercular cleft, contains 

 all of the sensory fibres of the ventral ramus c of the first 

 spinal and no others. The depressor muscle of the pec- 

 toral fin is innervated chiefly from the ramus ventralis c 



