MORPHOLOGY OF EYE MUSCLE NERVES 



129 



and that there are in Torpedo marmorata two transient gangha 

 associated with the trochlear anlage. Text figures C and D 

 illustrate Dohrn's argument. Corresponding with the four meso- 

 dermic segments which he claims are represented in the man- 

 dibular cavity Dohrn discovers two 'trochlear neuromeres' {tr'ch. 

 1; tr^ch. 2) and two trigeminal neuromeres (IV and V). The 



VII opt suy^^Vjj^^ '^ U'i'V-.-O;/ V J?' 



Text fig. C Horizontal section of a 9 mm. embryo of Torpedo marmorata, 

 after Dohrn ('07); cl.crs.n. 1, 'chiasma' group of cells; cl. crs.n. 2, anterior 'troch- 

 lear ganglion;' cl.crs.n. 3, second 'trochlear ganglion;' cl.crs.n. 4, Gasserian gan- 

 glion; VII.opt.su., ganglion of the r. ophth. sup. facialis; ///, IV, Neal's neuro- 

 meres. 



Text fig. D A parasagittal section of an embryo of Torpedo, after Dohrn 

 ('07); I-VII, neuromeres according to Neal ('98); tr'ch. 1, tr'ch. 2, Dohrn's troch- 

 lear neuromeres; IV, V , Dohrn's trigeminal neuromeres; VI, Dohrn's facialis 

 neuromere. 



two 'trochlear ganglia' found in Torpedo are seen in the frontal 

 section represented in figure 3. 



In support of the contention that the second myotome is poly- 

 meric and corresponds to at least two myotomes, Dohrn men- 

 tions the fact that from this myotome are differentiated two 



JOURNAL OF MORPHOLOGY, VOL. 25, NO. 1 



