Johnston, Nerves of Petro?nyzonts. 



583 



magnification, but they are essentially similar to the end plates in 

 the specialized muscle (see fig. 20). The endings in the specialized 

 muscles are more highly developed than these in the myotomes. 



Simple end-branching in the myotomes. — In figs. 14 and 15 are 

 shown other fibers which plunge directly into the myotomes. 

 These sometimes divide into two large branches. The coarse 

 fibers then run through the myotome toward the external surface 



Fig. 15. A section similar to the last, taken from the right side of the body. At the right is the 

 outer surface, at the left the section does not quite reach the notochord. The proximal portion of the 

 motor fibers, the epibranchial trunk and the dorsal nerves were drawn in from sections dorsal to that 

 from which the main part of the figure was taken, d.y., d.8, dorsal nerves; v.7, v.8, ventral nerves; 

 e-p., motor end-plates; ep.tr. ^ epibranchial trunk (vagus-lateralis-hypoglossus complex); X^, X^, third 

 and fourth branchial nerves of the vagus complex coming off from the epibranchial trunk; m.6, m.J, 

 postotic myotomes; g.4, point dorsal to the fourth gill opening. At the lower left hand corner four 

 motor cells from the spinal cord drawn at the same magnification. Magnification, 40 diameters. 



of the body and give off numerous branches to either side which 

 run parallel with the muscle fibers. These final branches are 

 moderately slender, slightly varicose fibers which show no sign 

 of any special end organ. I presume that they penetrate the 

 connective tissue separating the muscle bands and lie upon the 

 muscle fibers. In fig. 14 part of two fibers of this kind are drawn. 

 One of them divides into two branches. One branch is at first 



