ARRANGEMENT OF THE NERVE FIBRES. 203 



The investigation of the peripheral termination of the 

 nerve tubes — in the crude, incipient period they were erro- 

 neously regarded as a noose or loop-shaped connection be- 

 tween each two fibres — cost the histologists much trouble and 

 labor, and even at the present day we are still far removed 

 from a satisfactory scientific possession. We present only 

 the most important facts, and leave numerous, in part very 

 uncertain, minutiae to the more comprehensive text-books on 

 this subject. 



Let us commence with the termination of the motory nerve 

 fibres in the transversely striated muscle. 



If we follow the small nerve branches which have entered 

 the latter, in suitable objects, for example, many quite thin 

 membranous muscles of the frog, we meet with a few broad, 

 double contoured nerve fibres, subsequently surrounded by a 

 hyaline sheath. If the branch divides again, we not infre- 

 quently perceive that something new comes over the nerve 

 tube ; it becomes narrower, forming a Ranvier's constriction 

 ring (p. 195), and, at the same time, divides into branches, 

 two as a rule. With the continued division of these smallest 

 nerve trunks, this diminution of the nerve branches is con- 

 tinued ; they divide into branches of a new order, and so on. 

 The latter hereby become finer, but still retain the double 

 contours for a distance; at last they are bordered by a simple 

 boundary line. 



In the lower vertebrates this ramification of the primitive 

 tubes is very extensive. In fishes, the latter may finally 

 divide into fifty and even one hundred branches. Reichert, 

 many years ago, examined the so-called thoracic cutaneous 

 muscle of the frog. It contains from 160 to 180 muscular 

 filaments, but only from 7 to 10 nerve tubes pass in for their 

 supply. 



While, therefore, in the lower vertebrates a motory primi- 

 tive fibre supplies with its system of branches quite a number 

 of transversely striated muscular filaments, the arrangement 

 is different and higher in mammals (and even in reptiles and 

 birds). The primitive fibre is much less divided ; the mis- 



