THE PRIMARY VENTRAL ROOTS AND SOMATIC 

 MOTOR COLUMN OF AMBLYSTOMA 



G. E. COGHILL 



Denison University, Granville, Ohio 



TWENTY-EIGHT FIGURES 



Preliminary to the publication of studies upon the development 

 of the nervous system in relation to the development of behavior 

 in embryos of Amblystoma this paper is intended to record and 

 discuss briefly certain observations which, beyond their relation 

 to the general problem of correlation of growth and function, 

 have particular bearing upon the morphology of the nervous 

 system. These observations have to do with the nature of the 

 primary somatic motor column of the spinal cord and brain and 

 the relation of the primary ventral roots to the neurones of this 

 column. The general conception, growing out of the study of the 

 definitive ventral horn cell, seems to have been that the neurones 

 which form the ventral roots are a distinct type. The neurones, 

 however, which establish the earliest contact with the cells of 

 the myotome are found in Amblystoma to be at the same time 

 the neurones of the motor tract in the central nervous system. 

 The primary ventral root fiber is a collateral of a tract cell. It 

 is this discovery with which this communication is concerned. 



The species used chiefly in these studies is A. punctatum. 

 Occasionally A. opacum has been introduced but my observations 

 do not suggest that there is any difference between the two 

 species on the point under consideration. The specimens were 

 selected according to the physiological standards which an 

 earlier paper^ describes in detail. These standards are based on 

 the ability of the embryo to execute somatic movements in 



' Jour. Comp. Neur., vol. 19, no. 1. 



121 



