144 Journal of Comparative Neurology. 



(ground bundles) naturally accompanying the increase in the 

 abundance of substantia grisea. In cervical I the columna an- 

 terior is thinner than in the more caudal cervical segments, but 

 does not acquire a more sagittal position because of the greater 

 accumulation of descending (?) axones here than at levels cau- 

 dad to this segment. Here the depth of the columna anterior 

 is greater even than cervical VI. Its less thickness is due to the 

 absence of the columna lateralis, which is very evident in the 

 intumescentia cervicalis where it contains the cell-bodies of motor 

 neurones supplying the anterior extremities of the body. 



The coluninae posteriores are, as is to be expected, widely 

 deflected from the mid line in cervical I, due chiefly no doubt 

 to the great width of the funiculi posteriores (gracilis and cune- 

 atus) or the great accumulation of ascending axones, but in part 

 also due to an increase in the fasciculus proprius dorsalis. The 

 caput columnae posteriores is also thicker in cervical I than at 

 any other level, owing to a great abundance of substantia gela- 

 tinosa Rolandl This substance is also very abundant in the 

 sections involving the medulla oblongata (Figs. 2 and 3). At 

 the decussatio pyramidum (Fig. 3) the cervix is apparently 

 thinner because of the greater number of axones coursing in it, 

 producing the appearance of processi reticulares, but in this 

 section the columnae anteriores appear much as in cervical I. 

 only having less depth. In the thoracic segments, especially, 

 the distance of the caput columnae posterioris from the periph- 

 ery of the section (width of Lissauer's zone) appears relatively 

 great (Fig. i 1) as compared with the condition in the more fre- 

 quently studied specimens. According to Kopsch this distance 

 becomes less in the lumbar segments, a condition which must 

 be explained by the increase in the depths of the columna pos- 

 terior, for the axones composing Lissauer's zone (axones of 

 afferent neurones of the first order) must enter more abundantly 

 here from the larger radices posteriores than in the thoracic 

 segments. 



The total width of the gray figure (measurement 5) de- 

 creases with tolerable regularity from cervical I to the mid-thor- 

 acic segments. According to Kopsch's table, it begins to in- 



