MORPHOLOGY OF EYE MUSCLE NERVES 81 



the neural crest as described by Hoffman ('89), Oppel ('90), 

 Dohrn ('91), Miss Piatt ('91), and Froriep ('91) are secondary 

 and do not appear in the primary fibrillar stretch of the nerve 

 anlage. Filatoff ('07, p. 358) agrees with the writer ('98) 

 that the so-called primary trochlearis (Miss Piatt '91) has no 

 genetic relation with the definitive trochlearis, which develops 

 wholly independently of the neural crest and of the trigeminal 

 nerve, although it requires secondary connections with the latter. 

 According to Belogolowy ( '10a) no ganglion is associated with the 

 trochlear in bird embryos, while in the turtle the so-called ganglion 

 of the trochlearis has no connection with the trochlearis but is 

 connected with the superficial branch of the trigeminal (p. 424). 

 The same is true also of the relations of the ganglion in the stur- 

 geon. The superficialis nerve is, therefore, to be regarded as the 

 dorsal nerve of the trochlearis metamere. 



Schwalbe ('79, '81), Johnson ('05), and Carpenter ('06) have 

 asserted that the neuroblasts which form the nidulus of the troch- 

 lear are situated in the somatic motor column of the midbrain 

 and not in the hindbrain. Such divergent opinion may possibly 

 be explained by the fact that in the ventral portion of the brain 

 in this region no constriction is present such as that which divides 

 midbrain and hindbrain regions dorsally, so that it is difficult to 

 distinguish the limit of these two brain divisions. The majority 

 of investigators find the nidulus of the trochlear, either in the 

 hindbrain or in the isthmus. The assertion of Martin ('90), 

 that the nidulus of the trochlear is primarily in the visceral (lat- 

 eral) column, and that it secondarily migrates mediad, has not 

 been confirmed and, like many of the other amazing assertions 

 of this writer, should be placed in quarantine as suggested by 

 Dohrn ('07). In Squalus the nidulus of the trochlear is clearly 

 ventral and, while the fibrillar bundle of the nerve emerges dor- 

 sally from the brain wall in the region of constriction between 

 midbrain and cerebellum, the central fiber-tract with which it 

 is connected may be traced posteriad and ventrad to the nidulus 

 in the somatic motor column in the anterior portion of the cere- 

 bellar neuromere (neuromere iii). On the other hand. Van 

 Walkenburg ('10) finds two trochlear niduli in human embryos. 



JOURNAL OF MORPHOLOGY, VOL. 25, NO. 1 



