112 H. V. NEAL 



as well as some parts of the M. sternalis. Since there is no 

 median fin in the head region to prevent transmigration, it may 

 have occurred there as readily as in the ventral trunk and head 

 region. 



The vagrant nature of the superior oblique muscle is evinced 

 by the considerable variation in the origin and insertion of the 

 muscle as well as in its extended migration in the embryo. 



Several fairly obvious objections may be raised against Fiir- 

 bringer's ingenious hypothesis: First, the absence of any direct 

 evidence from comparative anatomy and embryology that any 

 vertebrate muscle has migrated in toto from one side of the 

 body to the other; Second, the complete failure of ontogenesis 

 to support the hypothesis. Ontogenesis is hardly so discredited, 

 even by Fiirbringer, that this lack of ontogenetic support can 

 be wholly ignored; Third, the total lack of evidence of an epi- 

 physial musculature. Nicholas ('00) did not demonstrate the 

 actual connection of rudimentary muscles with the epiphysis; 

 Fourth, the improbability of such a swapping of muscles as is 

 assumed in the hypothesis. Why the lateral eyes should lose 

 muscles which they already possessed and adopt those of an- 

 other degenerating organ is not perfectly obvious. Still other 

 objections might be mentioned but it seems unnecessary to 

 multiply them. 



Of course it may be said that no hypothesis dealing with 

 phylogenetic changes so remote as the origin of the trochlear 

 chiasma may be advanced which will seem so compelling as to 

 preclude criticism. To many, Fiirbringer's hypothesis will ap- 

 pear a reasonable one, on the assumption that nerve and muscle 

 are phylogenetically inseparable. The relations of the trochlear 

 and superior oblique muscle have always seemed a stumbling 

 block to the supporters of that assumption, the truth of which 

 does not seem more certain as the result of the difficulty of 

 explaining the chiasma of the trochlear. 



Fewer difficulties, it might appear, would meet an hypothesis 

 which assumed the secondary connection of nerve and muscle 

 by means of the free outgrowth of the nerve fibers. 



Johnston ('05, p. 210) suggests that: 



