^6 McCLURE. [Vol. IV. 



formed. The encephalomeres, after giving rise to their respec- 

 tive nerves, likewise degenerate.^ 



All nerves mentioned as originating from the centre of a 

 neuromere have reference to the dorsal or sensory root, unless 

 otherwise specified. Orr states that the ist, 3d, 5th and 6th 

 neuromeres in the hind-brain of the Lizard (neuromeres, tri- 

 gcmi7ial, facial, glossopharyngeal and vagus) give off (on each 

 side) from their dorsal half a mass of ganglion cells which con- 

 stitute the roots of the V. (VII., VIII.), IX. and X. nerves respec- 

 tively, and that the 4th neuromere (auditory neuromere) gives 

 off no nerve, but the space opposite to it is occupied by the 

 auditory vesicle. He also states that the VI. nerve arises, 

 though at a much later period than the others, from the ventral 

 portion of the 2nd neuromere (abducens neuromere). Beraneck 

 previously to Orr mentioned the fact that certain of the hind- 

 brain neuromeres of the Lizard held a definite relation to the 

 origin of the V., VII., VIII., and IXth nerves. 



My own observations upon the Lizard confirm the above 

 statements of Beraneck and those of Orr in every instance but 

 one; that is, in regard to the origin of the VI. nerve ^ from the 

 ventral portion of the 2nd neuromere of the hind-brain (abdu- 

 cens neuromere). That it originates ventral to the origin of 

 the other nerves, somewhere betivecn the origin of the V. and 

 VII. and VIII. nerves, there is no doubt, but I cannot defi- 

 nitely confirm its point of origin as stated by Orr from the 

 ventral portion of the 2nd neuromere. (See Fig. 5^, which is 

 a camera drawing of the hind-brain neuromeres of the Lizard.) 

 From an examination of this figure it will be seen that the V. 

 nerve arises from the trigeminal neuromere {Nvi V) ; that the 

 abducens neuromere {Nrn VI) gives rise to no dorsal root ; that 

 the facial neuromere {Nm J7I.) is connected with the origin 

 of the VII. and VIII. nerves; that the auditory neuromere 

 (xV;;z VIII.) gives off no nerve, but the space lateral to it is 



1 Orr states that the degeneration of the encephalomeres takes place in the hind- 

 brain of the Lizard as soon as the nerve fibres begin to develop. This point I did 

 not satisfactorily malce out, either for the neuromeres of the spinal cord or those of 

 the medulla, but I am inclined to think that Orr's statement is correct. 



^ The preliminary announcement of this paper, which appeared in the Zoolog- 

 ischer Anzeiger, No. 314, 1S89, states incorrectly on Orr's authority, that the VI. 

 nerve originates in connection with the most anterior neuromere of the hind-brain. 

 It should read that it arises from the ventral portion of the 2nd neuromere. 



