THE SPINAL NERVES. 75 



within which one runs cephalad and laterad, the other 

 caudad and laterad. The former, having reached almost 

 to the lateral edge of the dorsal musculature, sends a 

 small motor twig farther forward, then turns abruptly 

 caudad until, still within the same muscle, it joins the 

 caudal branch. Here the sensory fibres of both branches- 

 unite and, separating from the motor fibres, run up in 

 several bundles to supply the skin about the lateral line 

 near its junction with the supra-occipital commissure. In 

 their course toward the skin these sensory bundles run in 

 an intermuscular septum which is occupied by that limb 

 of the extra-scapular bone which articulates with the 

 cranium, and follow, some the outer, some the inner face 

 of that bone. Both branches of the r. medius b give off 

 motor fibres for the dorsal muscle throughout their entire 

 courses, and after their union and the separation of the 

 sensory fibres, their fibres at once distribute to the lateral 

 portion of that musculature. 



The large ventral ramus of b (r. v. b.) takes the remain- 

 ing motor fibres from that root and also a consider- 

 able bundle of sensory fibres. That the latter come from 

 the dorsal root b is from every standpoint very probable, 

 nay, almost certain, yet the sections do not afford an 

 absolute demonstration, as the ganglia of the two roots 

 cannot be sharply separated. The mixed ramus runs out 

 under the dorsal musculature, and is there joined by the 

 ventral ramus c {r. v.c), with which its further course 

 will be described. 



There is no r. communicans c. Some fibres from the 

 dorsal root c may, however, go out with the r. communi- 

 cans b, the double nature of the anastomosis of that nerve 

 with the r. lateralis accessorius offering a suggestion of 

 such a condition. 



