Oculomotor Nerve in Scy Ilium canicula. 



559 



motor to the ciliary ganglion, iSTeal says (14, p. 73) " If this conclusion be 

 confirmed — and this has been done by Belogolowy — it appears that at least 

 some of the medullary cells in the oculomotorius anlage are neuroblasts." 



Belogolowy (10) apparently only infers, however, that the cells of medullary 

 origin in the anlage of the oculomotorius are those which later enter the 

 ciliary ganglion. 



Gast('09) believes that, in the embryo, there exists a "root-ganglion" 

 upon the oculomotor nerve, the cells of which are of medullary origin. 

 Concerning this, ISTeal points out the difficulty of recognising with certainty 

 a nerve cell among the mass of cellular elements in the anlage of the nerve, 

 a difficulty to which I have already alluded.* 



Moreover, many of these cells of medullary origin are known to become 

 altered later into neurilemma elements, as do the similar cells in spinal 

 nerves. Carpenter has observed all stages in the differentiation of such 

 medullary cells into neurilemma, in the chick. Neal records that he, too, 

 has seen such a transformation, in embryo Squalus. His statement (14, 

 p. 74) is, ". . . in Squalus, it is possible to demonstrate that a large number, 

 if not all, of the cells present in the anlage of the oculomotor become 

 differentiated as neurilemma cells." 



In this connection Xeal reviews the evidence bearing upon the question : 

 To what extent, if at all, do emigrating medullary elements contribute to the 

 formation of the sympathetic ganglia related to spinal nerves ? The work 

 of Kuntz(ll) (which Neal remarks is "the latest presentation of the case 

 in favour of the medullary origin of some of the elements of the sympathetic") 

 comes in for somewhat severe criticism. Neal concludes that convincing 

 evidence " that cells of somatic motor nerve anlagen in Squalus . . . 

 migrate into the anlagen of the sympathetic is wanting. The assertions 

 of Kuntz in this connection appear quite unconvincing." 



As the result of his own observations aSTeal expresses the opinion (14, 

 p. 57) that "the evidence . . . seems rather to favour the view that the sym- 

 pathetic anlagen receive their cellular elements largely, if not exclusively, 

 from the sensory ganglia, as inferred by investigators upon all classes of 

 .vertebrates from Schenck and Birdsall to Held and Marcus." 



Thus, in contributing to the formation of the sympathetic (ciliary) anlage 

 tire oculomotor would, as a ventral root, appear to be altogether exceptional. 

 In the anlage of the oculomotorius, however, there are present cells which are 

 derived from the neural crest. 



The statement that free cell migration takes place from the mesocephalic 

 ganglionic mass towards the oculomotor anlage has been made by numerous 



* Vide p. 555, supra. 



