104 H. V. NEAL 



confirm this view. In other cases the oculomotor assumes very 

 close relations with the ganglionic placode connected with the 

 mesocephalic ganglion. Again, there is evidence of the anlagen 

 of sensory nerves in connection with the oculomotor. The proof 

 of this (p. 401) consists in the fact that a short cell-chain, free 

 from fibers, extends from the mesocephalic ganglion toward the 

 oculomotor anlage. The absence of a fiber in the cell-chain 

 appears to Gast to exclude the possibility that the cells are in 

 the process of migration centrad along a motor fiber of the ocu- 

 lomotor. On the other hand, Gast (p. 402) regards the evidence 

 given by Mitrophanow ('93) and Sedgwick ('92) in favor of the 

 mixed function of the oculomotor as fallacious. But Miss Piatt 

 ('91) may have seen what he regards as evidence of sensory 

 elements in the oculomotor. 



While Gast admits that this conclusion appears to conflict 

 with the evidence of the position of the nidulus of the oculo- 

 motor, he asks if it is not conceivable that Dohrn's suggestion 

 is correct — that the lateral and ventral niduli have united to- 

 gether. Then there is the possibility that the separation of 

 ventral and lateral niduli in the head region is a coenogenetic 

 separation and that they were primitively united. Gast, how- 

 ever, is of the opinion that the union of lateral and ventral 

 niduli assumed for the oculomotor is a secondary one, as Dohrn 

 suggested. 



On the basis of this supposition, Gast (p. 421) indulges in the 

 following speculation: 



The segmentally arranged mesocephalic-oculomotorius system with 

 its sensory and motor roots becomes secondarily separated into sensory 

 and motor elements, whereby the motor neurones of the oculomotor 

 retain their central connections, while the sensory neurones of the 

 mesocephalic ganglion acquire a new root. In the case of the Selachii 

 this root formation came to pass in such a way that a commissure 

 was formed between the individual ganglia of the anterior head 

 region (trigeminal, trochlear, mesocephalic and the ganglia anterior 

 to these). This commissural nerve gradually assumed the character 

 of a root, while fibers of the segmental sensory roots proportionally 

 degenerated. To-day, indications of these primary sensory roots 

 are found in the oculomotor as well as in the trochlear. 



