350 Journal of Coiiiparatiz'c Neurology and Psychology. 



thirty days the medullation is much heavier, and in the adult it 

 appears as dark as the corresponding area at the cervical level. 

 As at the cervical le\'el, the white matter is darker at the 

 border of the gray substance than at the periphery. 



Lumbar Level 



The light area noted in the fasciculus cuneatus of the lum- 

 bar level does not disappear quite so completely as the corre- 

 sponding areas of the more cephalic levels of the cord. By 

 the sixth da}' the medio-ventral part has become evenl}- medul- 

 lated, but at the eleventh day there is still an area in which 

 there has been little or no increase in medullation. Notwith- 

 standing the fact that in the lumbar level this light area was at 

 birth very faintly marked, a suggestion of it persists here longer 

 than in the levels above Even at thirty days it is not quite 

 lost in the general increase of medullary substance. 



The fasciculus gracilis does not appear in the lumbar cord 

 of thirty days, the dorsal funiculi being depressed in such a way 

 as to form a groove at this region. Numerous fibers in the en- 

 tering root zone and in the fasciculus cuneatus have made this 

 groove relatively less deep than at birth. At maturity this de- 

 pression can still be detected ; and the fasciculus gracilis, though 

 comparativeh- ver)- small, appears at this level. 



In the lumbar cord the crowding of the fibers in the groimd 

 bundle of the lateral and the ventral funiculi is not so conspicu- 

 ous as it has been higher up. Fibers radiating from the ventral 

 columns appear to be quite as numerous, but the longitudinally 

 coursing fibers are probably not so numerous. 



Summary of Changes in Medullation of the Medulla Spinalis Be- 

 tween Birth and Maturity 



I. In the cer\'ical and thoracic levels three areas in the 

 white substance are at birth noticeably lacking in medullated 

 fibers : 



a) the fasciculus gracilis, 



b) the pyramidal area in the fasciculus cuneatus, 



c) in the lateral funiculus an ill-defined area ventro-lateral 



to the substantia gelatinosa. 



[58I 



