300 JOURNAL oF COMPARATIVE NEUROLOGY. 
between the ventricular and the extra-ventricular mitoses re- 
mains practically constant for the same stages of growth. 
A comparison between the different levels of the cord was 
made only in the case of the new-born rat. 
TABLE III. 
Observations Based on 15 Consecutive Sections, Each Section 634 yu thick, 
from the Cervical, Thoracic and Lumbar Portions of the Cord of the New- 
Born Rat. 
Cord of New-Born Rat. 
Ventricular. Extra-Ventricular. 
nite Cervical I 26 
Thoracie 3 20 
Lumbar 8 45 
The lumbar cord resembles the cord of the foetus in the 
large number of mitoses, and in the relatively large number on 
the ventricular surfaces, while the thoracic cord shows a relative 
increase of extra-ventricular dividing cells, which is still more’ 
marked in the cervical cord. 
From the lumbar cord in the same series, 25 sections were 
examined, in order to determine the exact distribution of the 
mitotic figures. 
TABLE IV. 
Showing the Distribution of Mitoses in the Lumbar Cord of the New-Born 
Rat, from Observations on 25 Consecutive Sections, each 64% wu in Thickness. 
Lumbar Cord of New-Born Rat. 
Anterior gray column 61 
Posterior gray column 25 
Fiber tracts 8 
Ependyma Io! 
In the distribution of the mitoses throughout the cord, 
the anterior horns of the gray matter seem to be the ‘‘seat of 
predilection” in the new-born rat, the posterior horns following 
far behind. No counts were made in the older specimens to 
determine the exact distribution, but judging from a careful ex- 
amination, it is the anterior horns here also in which the greater 
number of mitoses are found. 
1 This number is slightly smaller than would be expected from the exami- 
nation of the 15 sections of the lumbar cord given above. 
