110 H. V. NEAL 



tral surface of the brain, while the trochlear has retained its 

 primitive position. It may readily be seen, however, that such 

 considerations have to do with the dorsal emergence of the 

 trochlear fibers rather than with the chiasma of the nerve. 



Martin's ('90) unconfirmed and incredible assertions regarding 

 the transmigration of the trochlear nidulus appear to deserve 

 no restatement, although they were accepted tentatively by both 

 Minot ('92) and Kolliker ('96) so far as they relate to a central 

 origin of the trochlear chiasma. Kolliker, however, finds it diffi- 

 cult to conceive of a transmigration of a nidulus, although von 

 Lenhossek and Ram6n y Cajal have inferred a migration of 

 neuroblasts from the ventral column of the tube into the sen- 

 sory roots. An extensive migration of neuroblasts therefore ap- 

 pears possible. 



Fiirbringer ('02, pp. 134-136) has given the most thorough 

 consideration to the problem of the chiasma of the trochlear and 

 his hypothesis, although affected by his views of the primary 

 and unalterable connection of nerve and muscle, seems to be 

 the most elaborate of all that have been advanced. Following 

 an idea advanced earlier by Hoffmann ('89), Fiirbringer suggests 

 that the trochlearis may have innervated musculature belonging 

 to the parietal eye. According to Fiirbringer the parietal eye 

 (or pau' of eyes) was situated primarily near the paired lateral 

 eyes, which were then slightly differentiated and probably occu- 

 pied a more dorsal position than later. The aberrant muscula- 

 ture connected with both kinds of eyes may have very early 

 separated itself — as the course of the nerve indicates — from the 

 dorsal portions of the neighboring myotomes and may, in corre- 

 lation with the primitive condition of the eyes, have been in a 

 very slightly differentiated and — so to speak — fluid condition, 

 with its fibers extending in various directions. Those portions 

 of the muscle which extended somewhat diagonally or trans- 

 versely had the tendency, like other muscles extending toward 

 the median line of the body, to migrate over into antimeric 

 territory. There was nothing hke a median fin in the region to 

 hinder this migration,, which could occur freely. 



With the degeneration of the parietal eye the musculature 

 which became associated with it disappeared. The muscles of 



