SPINAL NERVES IN VERTEBRATES 141 



join to form the motor ramus for the back. Likewise the two 

 anterior roots unite in a ventral motor ramus, which joins the 

 ventral sensory ramus in forming a mixed ramus ventralis. 

 The dorsal sensory rami remamed entirely separated from the 

 motor rami, and the condition in Myxine is said to be similar 

 to that in Bdellostoma. Miss Worthington's description for 

 the distribution of the first spinal nerve in Bdellostoma resembles 

 in the main the description of Ransom and Thompson, but is 

 more complete, and the nerve is figured in her reconstruction 

 of the cranial nerves (fig. 14). She finds that the first spinal 

 nerve in Bdellostoma has one sensory and two motor roots, and 

 states that the motor roots emerge from a Y-shaped foramen 

 as one trunk. The spinal ganglion is said to be elongate, having 

 a dorsal and a lateral arm. The dorsal arm gives rise to the 

 dorsal sensory ramus, and the ventral, to the ventral sensory 

 ramus. The ventral root continues ventrad as the ventral 

 motor trunk, and unites with the corresponding sensory trunk 

 to form the ramus ventralis. Close to the origin of this trunk, 

 a branch, said to represent Fiirbringer's dorsal motor trunk, 

 is described and figured as passing dorsad to penetrate the body 

 muscles. From its source this dorsal branch might be expected 

 to possess sensory as well as motor fibers. 



Cole in his paper on the muscles of Myxine figures a typical 

 abdominal transverse section, incorporating in it all of the nervous 

 elements found in that segment. A dorsal (sensory) root is 

 figured as passing through the neural arch and expanding on the 

 outside in a ganglion, from which a dorsal and a ventral ramus 

 are given off. The motor fibers are figured as issuing by four 

 rootlets into two roots, which apparently penetrate the neural 

 arch through separate foramina. Outside the neural arch one 

 of the roots is represented as giving off a dorsal branch, which 

 joins a corresponding sensory trunk in forming the ramus dor- 

 salis. The two ventral roots unite opposite the notochord, 

 producing a short motor trunk, which joins the ventral sensory 

 ramus in the formation of the ramus ventralis. Both the ramus 

 dorsalis and the ramus ventralis are shown in his figure as trav- 

 ersing the inner surface of the myotome, the former pierces the 



