No. 2.] A MIA AND TELEOSTS. 89 



together, and the common ganglionic mass formed on them lay- 

 always posterior to the septum. 



From this ganglion three dorsal, three ventral, and two hori- 

 zontal branches arise, but as the anterior one of the two latter 

 branches soon separates into two nearly equal parts, there are 

 thus three horizontal branches, in all, associated with the 

 ganglion. The three dorsal and three horizontal branches 

 are distributed to the fourth, third, and second muscle- 

 segments, in a manner similar to that of the corresponding 

 branches in the posterior segments. The three ventral 

 branches unite to form a single nerve which, after being 

 joined by a branch of the nerve of the fifth segment, is dis- 

 tributed, as above stated, to the sternohyoideus muscle and to 

 the muscles of the pectoral fin. As the branches of these 

 three segmental nerves all arise from a single ganglion, there 

 were naturally no anterior communicating branches associated 

 with them. 



There was no indication whatever of a separate nerve related 

 to the first muscle-segment, and no branches of the nerve of 

 the second segment could be traced forward into it. 



In Amia, the four spino-occipital nerves belong to the second, 

 third, fourth, and fifth muscle-segments, there being in Amia, 

 as in Scomber, no separate nerve related to the first segment. 

 The nerves of the second and third segments issue from the 

 cranium through foramina in the occipitale laterale, the next 

 two issuing through apertures in the membranes that fill the 

 spaces between the cranium and the occipital arches. The first 

 two nerves are represented by ventral roots only, the other two 

 by both dorsal and ventral roots. All four of the nerves take 

 part, as do the nerves of the corresponding segments in 

 Scomber, in the innervation of the sternohyoideus muscle, 

 and a part of the fourth nerve joins the nerve of the sixth 

 muscle-segment to form the nervus pterygiaHs. Posterior to 

 the nerve of the sixth segment several other nerves enter, 

 independently, the pectoral fin. 



We thus see that the first six muscle-segments of the trunk 

 of Scomber closely agree, in their relations to the dermal bones 

 of the cranium and shoulder girdle, with the corresponding 



