122 H. V. NEAL 



ston writes (p. 584): ''There seems to be no definite or constant 

 arrangement of these motor fibers. They pass in a haphazard 

 fashion to one or two myotomes, branch once, twice or three 

 times, et cetera. In studying the peripheral nerves of Am- 

 phioxus with methylene blue I gained the general impression 

 that the nerves in that animal showed still less regard for seg- 

 mental relations." The point of these statements in this con- 

 nection is, not the fact* of irregularity of nerve relationships in 

 these primitive chordates, but the evidence against the view of 

 the inseparability of muscle and nerve, afforded by them. Such 

 facts point unmistakably toward the possibility of changed inner- 

 vation under changed conditions. Moreover, the more recent 

 conclusions regarding the phylogeny of the nervous system 

 (Parker '10) are against the view of the primary continuity of 

 nerve and muscle. 



Still further in confirmation of the view that the abducens has 

 acquired its present relations by a process of substitution, is 

 the fact to which my attention has been called by Dr. W. H. 

 Lewis, that when the digastricus first arises in the human embryo 

 it is innervated by the facial nerve. Later in development, the 

 muscle divides and the anterior belly becomes innervated by a 

 branch of the trigeminal. If such a process of nerve piracy 

 occur ontogentically, it is clearly possible that a similar process 

 may have taken place phylogenetically in the case of the abducens. 



h. How may the innervation of musculature derived from two 

 somites by a single nerve — the abducens — be best interpreted? The 

 majority of investigators have confirmed Van Wijhe's statement 

 that the musculature innervated by the oculomotor is derived 

 from the first or pre-mandibular somite; that innervated by the 

 trochlear is differentiated from the second or mandibular somite; 

 while the abducens musculature is developed from the third 

 somite. That is, each eye-muscle nerve is distributed to a single 

 somite. With the exception of Dohrn ('01, '04) all students of 

 the genesis of the eye muscles including Kastschenko ('88), Miss 

 Piatt ('91), Hoflmann ('97), Neal ('98), Sewertzoff ('99) and 

 Lamb ('02), agree upon the monomyotomic distribution of these 

 nerves. Belogolowy ('10 a, p. 252) finds that the anlage of the 



