142 



bulletin: museum of comparative zoology. 



Notes on Later Develop- 

 ment 200 



1. Oculomotor Nerve . 200 



2. Ophthalmic Branch 



of the Trigeminal 



Nerve 201 



3. Ciliary Ganglion . . 201 



4. Abducent Nerve . . 202 



5. Eye Muscles ... 202 



6. Trochlear Nerve . . 202 



PAGB 



Discussion of Results .... 202 



Migration of Medullary Cells . 202 



Histogenesis of the Neuraxons 205 



Nature of the Ciliary Ganglion 205 

 Homologies of the Oculomotor 



and Abducent Nerves . . . 209 



Summary of Results 210 



Bibliography 214 



Explanation of Plates 228 



Introduction. 



" Vo;? alien motorischen ISTerven ist mit Ausnabme vielleicht des 

 Hypoglossus kein anderer zum Gegenstand so widerspruchsvoller An- 

 gaben und Deutungen geworden, wie der Oculomotorius. Er ist als dor- 

 saler, als ventraler und als gemiscbter Nerv in Anspruch genommen 

 worden ; man hat ihm metamerischen Wertb zu- und abgesprochen ; er 

 ist als Theilstiick des Trigeminus definirt, und ihm sind alle Beziehungen 

 zum Trigeminus geleugnet worden. Man hat Ganglien an ihm ent- 

 cleckt, deren Ursprungsort man in der Ganglienleiste sah ; man hielt sie 

 dann fur eine Abspaltung des G. ciliare ; man schrieb sie einem eigenen 

 G. oculomotorii zu, das nichts mit dem G. ciliare zu thun babe ; man 

 leugnete die Ganglien ganz und gar — kurz es war nicht mit ihm fertig 

 zu werden." — Dohrn ('91, p. 2). 



Since Dohrn commented thus in 1891 upon the diversity of opinion 

 which exists concerning the oculomotor nerve and the ciliary ganglion, 

 three investigators have added still another to the already large number 

 of conflicting statements. They have asserted that in selachians the 

 oculomotor nerve grows from the mesocephalic ganglion to the ventral 

 face of the mid-brain, and not in the opposite direction, as had pre- 

 viously been supposed. Dohrn himself, in the article from which the 

 quotation is taken, described an entirely new mode of origin for the cells 

 of the ciliary ganglion, namely, migration from the neural tube into the 

 root of the oculomotor nerve. 



This lack of agreement in regard to the developmental history of the 

 oculomotor nerve, and particularly of the ciliary ganglion, seemed a suffi- 

 cient justification for a renewed study of the subject. In the case of 

 the abducent nerve, opinions of observers being more in accord, a study 

 of its development might be expected to result in little more than a 

 confirmation of generally accepted views. Though primarily concerned 

 with the oculomotor nerve and ciliary ganglion, I have, nevertheless, 



