424 CHARLES HILL, 



the brain, but are very evenly distributed. In these stages the only 

 criteria, by which I have counted neural segments, are external and 

 corresponding internal transverse constrictions or grooves. 



The segmental value of the cranial nerves, while important, has 

 so frequently been shown to be deceptive and misleading (McClure, 

 '89; MiNOT, '92; Locy, '95, and Neal, '98), that it is unnecessary here 

 to repeat this evidence. While recognizing that the deep origin of the 

 cranial nerves is the important criterion, I wish here merely to locate 

 their union with the brain in order to establish more accurately the 

 identity of the individual neuromeres, as described here, with those 

 of other observers. I have found the same nerve connection in the 

 trout as in the chick. The following description therefore, applies to 

 either type. 



The olfactory and optic nerves are connected respectively with 

 the first and second segments. From the ventral region of the raid- 

 brain and the posterior portion of segment 4 the fibres of the oculo- 

 motor nerves (Fig. 21) pass ventrally and laterally, close to the ciliary 

 ganglion and innervate the fundament of the muscles of the eye. 



The fourth pair of nerves are connected with the dorsal and 

 posterior region of the mid-brain or segment 5. 



Laterally and in the dorsal portion of segment 6, the fibres of 

 the anterior root of the Trigeminus emerge and pass to the Gasserian 

 ganglion (Fig. 48 ant. rt. V). 



From segment 7 the main fibres of the trigeminal nerve pass 

 cephalad to the Gasserian ganglion (Fig. 49 and 50). 



Segment 8 has no nerve connection. 



Segment 9 gives rise to the fibres of the seventh and eighth pair 

 of nerves (Fig. 49 and 50 VII and VIII). 



Segment 11 is connected with the fibres of the ninth pair of 

 cranial nerves (Fig. 50). 



I also confirm the observation of Miss Platt, Hoffmann and 

 Locy that the origin of cranial nerves is from the external depres- 

 sions, between adjacent segments. 



III. General Considerations. 

 Identifications of Neural Segments. 



In discussing metamerism of the head it should be borne in mind 

 that the neural segmentation is merely an expression of the general 

 segmentation of the body. This primary division into joints is not 



