108 H. V. NEAL 



at the place of union of the anlagen of the superficiahs and 

 the trochlear is that it is sympathetic. Like the cells of all 

 sympathetic ganglia those of the trochlearis appear to come 

 from a sensory ganglion. In both instances they collect in the 

 region where sensory and motor fibers unite. Against this view 

 may be urged the fact that there is no sympathetic in relation 

 to the adult trochlear nerve. But the objection loses much of 

 its force when it is remembered that transient sympathetic gan- 

 glia are not uncommonly found in the trunk region of elasmo- 

 branchs. 



This supposed sympathetic ganglion of the trochlear anlage 

 must not be confused with those fragments of the neural crest 

 which Dohrn ('85) and others have called ganglia of the troch- 

 learis. Such 'ganglia' appear, as suggested by Dohrn ('07) and 

 Gast ('09), to be comparable with degenerated portions of the 

 superficial nerve and not with sympathetic ganglia. Belogolowy 

 ('10 b) finds in reptile embryos a ganglion present at the point 

 of anastomosis of the trochlearis anlage with the ramus ophthal- 

 micus superficiahs trigemini. Belogolowy expresses the opinion 

 (p. .70) that the so-called ganglia of the trochlearis are really 

 the ramus ophthalmicus superficiahs trigemini which is repre- 

 sented in some 'forms by scattered clumps of cells. With this 

 opinion the writer is in full accord. 



b. How may the innervation of a muscle derived from a somite 

 {Van Wijhe's second) also innervated by the abducens be inter- 

 preted? Another problem presented by the relations of the troch- 

 lear is the fact that it innervates a muscle derived from a somite 

 also supplied by the abducens nerve. This comes about in the 

 following manner: A portion of the myotome of Van Wijhe's 

 second somite unites with the myotome of the third somite to 

 form the posterior rectus muscle. Miss Piatt ('91), with char- 

 acteristic accuracy, observed this connection, but was led to 

 infer its later degeneration and to confirm the conclusion of 

 Van Wijhe ('82) that the posterior rectus muscle is derived ex- 

 clusively from the third somite. Lamb ('02) reached the same 

 conclusion. But Dohrn ('07), after a careful reinvestigation of 

 the development of the superior oblique muscle, asserted the 



