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Nachdruck verboten. 



On the segmental Structure of the Motor Nerve-plexus. 



By E. S. Goodrich. 



In a paper on the median and paired Fins of Fish (Quart. Jour- 

 nal of Microsc. Science, Vol. 50, 1906) I endeavoured to show that 

 the radial fin-muscles of Elasmobranchs preserve their original meta- 

 meric order and independence. It is wellknown that these . muscles 

 develop in each segment from two muscle-buds, which grow out into 

 the fin fold, divide into dorsal and ventral buds, and give rise to the 

 two dorsal and two ventral radial muscles of the adult fin. Since 

 each myotome receives its motor supply from one spinal nerve only, 

 the four radial muscles should be supplied only by the one spinal 

 nerve belonging to the myotome from which they arose. Now, in the 

 paper mentioned above, I contended that this is really the case, and 

 supported my argument with evidence afforded by the experimental 

 stimulation of the nerves. 



Dr. Beaus has recently published a paper (Experimentelle Unter- 

 suchungen über die Segmentalstruktur der motorischen Nervenplexus, 

 Anat. Anz., Bd. 34, p. 529) in which he adversely criticises my meth- 

 ods and results, and maintains that each spinal nerve may supply 

 not only the muscles corresponding to its own segment, but also the 

 neighbouring muscles; that the motor nerves form a plexus of over- 

 lapping branches, and that the nerve-supply is no longer segmental. 

 In Scyllium Braus finds that a single nerve may supply 6 or 7 radial 

 muscles. 



Last December I repeated ray experiments most carefully at the 

 Marine Biological Laboratory in Plymouth, with the help of excellent 

 instruments kindly lent to me by Prof. Gotch, and with the assist- 

 ance of Mr. Speyer. It must at once be confessed that the results 

 of these new experiments convinced me that Braus is right in his 

 contention that the strict metamerism is lost, and that I was wrong 

 in maintaining the opposite view. 



Nevertheless, our results do not agree, and I am not at all 

 prepared to accept all his conclusions. The experiments are not easy 

 to carry out, and the sources of error are many. The radial muscles 

 are closely packed together, bound together by connective tissue, and 



