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Nachdruck verboten. 



The Encephalomeres and Cranial Nerres of an Embryo 

 of Acanthias vulgaris. 



By Professor Alexander Meek. 



With one Figure. 



A review of the literature dealing with the primitive segmentation 

 of the vertebrate head and brain, especially the works of Locy, Hill, 

 Neal, and v. Kupffer, serves to show that there are eleven brain 

 segments rather clearly defined anteriorly in front of a region occupied 

 by somites where the neuromeres are not so prominent. In this posterior 

 region of the brain, however, they can be traced as a series of swell- 

 ings of the neural canal regularly alternating with the somites, and 

 they are continued backwards in the body as the neuromeres (myelo- 

 meres) of the spinal cord. It has been suggested by several authors 

 that the neuromeres are produced by the pressure of the somites on 

 the neural canal, but the fact is that the folds are more clearly marked 

 in the region not occupied by somites. The further dififerentiation of 

 the brain shows moreover with remarkable constancy that the first 

 three brain segments are concerned in the formation of the pros- 

 encephalon, the next two with the mesencephalon and the remaining 

 six together with a number of succeeding encephalomeres go to make 

 the metencephalon. There is also a very close agreement amongst 

 the writers with regard to the nerves in relation to the neuromeres, 

 at all events so far as the anterior nine segments are concerned. 



In a previous paper i) I was able to state the nerve relationships 

 of the encephalomeres of the Lesser Black-backed Gull, Larus fuscus L., 

 and I also attempted to indicate the number of the brain segments 

 incorporated in the brain. Like my predecessors I found that the 

 second rhombomere was connected with the trigeminal and the fourth 

 rhombomere with the facial and auditory. The gull material also 

 demonstrated in the most unmistakeable manner that the fifth and 

 sixth rhombomeres, which occur opposite the auditory vesicle, gave 



1) Anat. Anz., Bd. 31, 1907, p. 408. 



