348 EDWIN S. GOODiaCH. 



it becomes connected. In the case of the Gadida?, witli jug-uhnr 

 pelvic fins, it is clear that these have moved to their position 

 in front of the pectorals. But — and this is the important 

 tiling" to remember — these limbs do not really lose their 

 original connections, the displacement can be traced 

 in ontogeny, and the nerve supply in the adult in- 

 fallibly betrays its course. 



The Faithfulness of Muscle and Nerve. 



That in a series of metameric myotomes and nerves 

 each motor nerve remains faithful to its myotome, 

 throughout the vicissitudes of phylogenetic and ontogenetic 

 modification, may surely be considered as established. That 

 a motor nerve is unable to forsake the muscle in connection 

 with which it was originally developed to become attached to 

 some other seems to be in the highest degree probable, both 

 on physiological and on anatomical grounds. As a matter of 

 fact, this appears always to be the case in the development 

 of limbs. 



Now, the paired limbs, and also the median fins, are supplied 

 by branches from a number of segmental nerves forming a 

 " limb plexus." In such a plexus the branches may fuse to 

 common stems, or become joined together by connecting twigs, 

 so that the nerve - fibres appear to become inextricably 

 mixed; at all events, they form a network of mixed fibres 

 (motor and sensory). The motor "plexus" of a limb, so far 

 as it can be said to exist (see p. 3G6), is brought about, not 

 by the nerve deserting one muscle for the sake of another, 

 but by the combination of muscles derived from 

 n e i g h b o u r i n g segments. (I venture to make this dogmatic 

 statement in spite of the fact that the embryological evidence 

 is still, unfortunately, very incomplete because it seems to me 

 to result inevitably from what has been ascertained concerning 

 the anatomy and development of nniscles and nerves generally.) 



We may thus get compound muscles formed which receive 

 motor branches from more than one spinnl nerve. Rti-ictly 



