22 H. V. NEAL 



only the answer to tKe problem of the morphology of the eye 

 muscles and their nerves but also general conclusions regarding 

 the phylogenesis of the vertebrate head. For it may readily be 

 seen that if nerves are ab initio connected with their terminal- 

 organs, all the modifications of the latter would naturallj' be 

 accompanied by associated changes of the former. If, for ex- 

 ample, a post-otic nerve innervates a pre-otic muscle, upon the 

 assumption of an immutable connection of nerve and muscle, 

 the inference that the muscle had migrated from behind the ear 

 into its present position and carried its nerve with it, might 

 appear the most reasonable interpretation of such a peculiar 

 relationship. But if, on the other hand, a nerve is not invariably 

 associated with a given muscle throughout its phylogenetic his- 

 tory, but may grow into muscular territory primitively foreign 

 to it, such an assumption would greatly modify our views of 

 nerve and muscle phylogenesis and possibly our views of the 

 history of the vertebrate head. 



The h.istogenetic problem of neuro-muscular relations there- 

 fore appears fundamental to any problem, such as that of the 

 morphology of the vertebrate head, involving nerve and muscle 

 in complex and obviously modified relations. Upon the answer 

 to this problem depends, for example, the answer to the prob- 

 lem of the present singular muscular relations, of the trochlear 

 and abducens nerves. While it is an unquestioned fact that 

 nerve and muscle tenaciously retain connections once acquired, 

 and while this conservatism of relation may be taken as a basic 

 assumption in morphology, the possibility still remains that under 

 changed conditions new neuro-muscular relations may be ac- 

 quired. If Gegenbaur and Fiirbringer be correct, such changes 

 are as incredible as, for example, the inheritance of mutilations 

 are believed to be. But, on the other hand, to all of those who 

 have come to accept the process theory of nerve development 

 and who therefore assume the secondary connection of nerve 

 and muscle, the invasion of new territory and its piratical seiz- 

 ure by exotic nerves appears a possibility. A discussion of the 

 present problem, therefore, does not lead the morphologist far 

 afield. The history of the head must be written primarily in 

 terms of nerve histogenesis. 



