MORPHOLOGY OF EYE MUSCLE NERVES 119 



McMurrich ('12) has recently advanced a theory (p. 175) 

 which involves the assumption of this migration of post-otic 

 myotomes into pre-otic relationships. Johnston ('02 and '05, 

 pp. 230-233) has in my opinion completely refuted Fiirbringer's 

 argument in favor of the phylogenetic migration forward of 

 trunk nerves and myotomes into the occipital region. To all 

 who hold the view of the primary continuity of nerve and muscle 

 the hypothesis will seem the only tenable one, in spite of obvious 

 difficulties and objections. Belogolowy ('10 a, pp. 380-384) has 

 recently advanced an extended argument against the hypothesis 

 of the primary continuity of nerve and muscle. 



The most obvious objection to this hypothesis is the entire 

 lack of ontogenetic evidence in its support. Had the phylo- 

 genetic migration of muscle assumed by the hypothesis actually 

 occurred, we should expect to find some ontogenetic evidence 

 of it. But there is as little ontogenetic evidence that the so- 

 mites from which the posterior rectus muscle develops have 

 migrated from behind the ear as that the mandibular and hyoid 

 arches with which they are associated topographically have mi- 

 grated from a post-otic position into their present location in 

 the embryo. Furthermore, the hypothesis cannot be reconciled 

 with the fact that the abducens — a post-otic nerve — innervates 

 a myotome (Van Wijhe's 2nd) of which a dorsal moiety is 

 innervated by the trochlearis, a nerve with a pre-otic nidulus 

 (fig. 81). The niduli of these two nerves lie in widely separated 

 neuromeres of the brain — one of them pre-otic and one-post- 

 otic — and yet they innervate muscles derived from the same 

 somite. If the posterior rectus muscle were once post-otic, it 

 is difficult to explain how the somite from which it is in part 

 derived (Van Wijhe's 2nd) is innervated also by a pre-otic nerve 

 with a pre-otic nidulus. If the hypothesis were true, it would 

 be necessary to assume a migration of the nidulus of the troch- 

 learis from behind the ear into its present position. Of such a 

 migration of a motor nidulus from one metamere into another 

 several segments removed, there is neither comparative anatom- 

 ical nor embryological evidence. The careful comparative ana- 

 tomical investigation of the nidulus of the abducens by Kappers 

 ('10) discloses no such migration of the nidulus as McMurrich's 



