Oculomotor Nerve in Scvllium canicula. 



565 



a sympathetic ganglion to both the ventral and dorsal roots of its related 

 spinal nerve. 



Xeal, discussing the question of the relation of the oculomotorius to the 

 ramus profundus, decides (14, p. 102), " there appears to be no insuperable 

 objection to the view that the ophthalmicus profundus is serially homologous 

 with spinal somatic sensory nerves." "While this is readily conceded, it falls 

 short of establishing that the ramus profundus necessarily represents the 

 sensory root in the oculomotor neuromere. Xeal continues : " The comparison 

 of the profundus nerve with spinal somatic sensory nerves is still further 

 strengthened by the evidence of the relations with the ciliary ganglion, which 

 have been found above to be those of a somatic motor nerve to a sympathetic 

 ganglion. The facts which prove the s)'mpathetic character of the ciliary 

 anlage have already been stated above and need no restatement. The ciliary 

 ganglion of Squalus is to be regarded as partly, if not exclusively, a sympathetic 

 ganglion. So that in its relations with a sympathetic ganglion the oculo- 

 motor forms no exception in the series of morphologically similar somatic 

 motor nerves." 



From what we know of the development of the ciliary ganglion, however, 

 this relation may, quite as reasonably, be interpreted upon the hypothesis of 

 the segmental distinctness of the two nerves. In accordance with which, I 

 suggest that the ciliary ganglion is to be regarded as the product of the 

 fusion of sympathetic ganglia related to at least two segmentally distinct 

 cranial nerves. Such a condition is paralleled in the spinal region in the 

 cervical ganglia, for example. Even if we admit the correctness of Krause's 

 view that the ciliary ganglion has a double nature (containing, in addition to 

 its sympathetic elements, the bipolar cells of a cerebro-spinal ganglion), the 

 comparison of the oculomotor nerve with a typical segmental nerve would 

 not be affected. "We should merely recognise that certain cells, migrating to 

 the ciliary ganglion along the fibres of the oculomotor and ophthalmicus 

 nerves, which were hitherto supposed to be simply sympathetic cells, were, 

 in fact, sensory cells. 



It may well be that the ciliary ganglion is not strictly homologous in all 

 species. The oculomotor ganglion has been observed in but comparatively 

 few species, and, while its presence will probably be revealed by further 

 investigation in many other forms, yet it is scarcely credible that it can 

 have been completely overlooked in many types which have been carefully 

 studied. In such forms, then, the cells of the oculomotor ganglion may have 

 migrated into the proximity of, or even into actual fusion with, the ciliary 

 ganglion, which would thus have the double character claimed for it by 

 Krause. On the other hand, in those species in which a distinct oculomotor 



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