142 



bulletin: museum of compakative 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 



1 PAQB 



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 Besults 210 



Bibliography . 214 



Explanation of Plates 228 



Introduction. 



"Von alien motorisohen Nerven ist mit Ausnahme vielleicht des 

 Hypoglossus kein anderer zum Gegenstand so widerspruchsvoller An- 

 gabeh und Deiitungen geworden, wie der Oculomotorius. Er ist als dor- 

 saler, als ventraler und als gemischter Nerv in Anspruch genommen 

 worden ; man hat ihm metaraerischen Werth zu- und abgesprochen ; er 

 ist als Theilsttiek des Trigeminus definirt, und ihm sind alle Beziehungeu 

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

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

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

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

 leugnete die Ganglion 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 

 iace 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 

 Toot of the oculomotor nerve. 



This Jack 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, 



