134 Journal of Comparative Neurology. 



divided into short pieces at the time of its fixation and conse- 

 quently measurements would have involved considerable error. 



The specimen described by Kopsch was removed entire 

 and placed in Muller's fluid. In this fluid it remained for more 

 than two years. Upon the renewal of its study it was washed 

 in seventy percent, alcohol for about two weeks, then photo- 

 graphed and a drawing made for purposes of orientation. In 

 the further study, various other measurements were made. One 

 set of these deals with the length of the lines, or the areas of 

 pia mater, alpng which the fila radicularia of the dorsal and 

 ventral radices of the various segments enter or leave the me- 

 dulla spinalis (zones of entrance and exit). One general differ- 

 ence between the the two radices brought out by these meas- 

 urements is that the line along wliich the radix posterior of a 

 given nerve enters the pia is always shorter than that along 

 which the corresponding radix anterior emerges. This, of 

 course, results in a greater space of pia between the fila radi- 

 dularia of adjacent radices posteriores than between the cor- 

 responding radices anteriores. This difference existed very 

 evidently in the Bridgeport specimen and so far as the author 

 is aware is true for vertebrates generally. It is but an expres- 

 sion of the fact that the fila of the radix posterior of a given 

 nerve are thicker and fewer in number than those of its radix 

 anterior. The former result from the division of the radix pos- 

 terior before entering the pia along the sulcus lateralis posterior. 

 The axones composing them iiave their origin in definite separ- 

 ated cell masses, the ganglia spinalia, while the fila of the radix 

 anterior have their origin in a continuous column of cell bodies, 

 the columna anterior of the medulla spinalis, and in the process 

 of collecting to form the radices anteriores, emerge through the 

 pia as a greater number of more finely divided filaments and in 

 a more nearly continuous line. 



The width or space between the mid line and these lines 

 of entrance and exit of the different radices was observed to 

 uniformly increase in passing from the caudal to the encephalic 

 end of the specimen (Fig. i, plate IX). This also is a feature 

 common to other species. It but indicates that the ascending 



