THE SEGMENTAL VALUE OF THE CRANIAL NERVES. 



By A. ALilnes Marshall, 31, A., D.Sc, Felloiv of St. John's College, 

 Cambridge ; Beyer Professor of Zoology in Owens College. 



[The references are to Plates V & VI of the preceding paper.] 



Whether the nerves arising from the brain are directly comparable to 

 those taking their origin from the spinal cord, and, if so, to how many 

 pairs of the more symmetrically arranged spinal nerves the cranial 

 ones are equivalent, are questions which have attracted the attention 

 and exercised the ingenuity of many of the greatest anatomists, 

 and which have been answered in the most varied senses by the 

 different writers who have attempted to grapple with their difficulties. 

 So long as the problems were attacked from the morphological side 

 alone, as was the case with all the earlier attempts to solve them, the 

 answers obtained were vague, inconclusive, and mutually contra- 

 dictory ; but since the clear light of embryology has been directed 

 upon them, the clouds of uncertainty have been to a very considerable 

 extent dispersed, and there is now, especially amongst those who have 

 most recently dealt with these questions, a very considerable and 

 satisfactory agreement as to the main outlines of the answers to be 

 given, although in many points of detail there is still much dis- 

 crepancy between the several accounts. 



The present paper is an attempt to set forth the actual position of 

 these problems, and the leading phases through which they have 

 passed in their gradual maturation. In preparing it I have made 



