llli: OK..ANS <>F Till: 





419 



canal and the spongiosa (spon^iolila.M d Hi~). and (2) into 

 which arc transformed into LraiiL'lionir c. 11s and m-i\ --fibres (lie 



Masts t f HIM. [the thickening of tlie lateral walls dep<>nd> pai-tly 

 upon the multiplication of n-ll>. imt mainly u| M-I thatnerve- 



lil >ies apply themselves to th cell mavs from tin- outside. In time 

 thi-M- lil-i into the anterior, lateral, an-1 p. .-t 



columns of the spinal conl (li-;. L'. 1 ;:} p,-n\ A-//-, acw). At tia-ir lir>t 

 appearaiu-e thenerve- 

 fi!>re> are non-mcdul- 

 lated (fig, -l\-2 ,if), 

 and only s ubse- 



earlier, sometimes 

 later, acquire a me- 

 dullary sheath. In 

 this manner tin- al- 

 icady considerably 

 thickt-neil halves of 

 I'inal cord be- 

 come differentiated 

 into the central gray 

 suK-tanco containing 

 the ganglionic cells, 

 and into the white 

 which en- 

 the surface of 

 the former like a 

 mantle. 



Since, meanwhile, 

 the roof- and tloor- 

 I'latcs iri'ow only a 

 little and are not 

 diil'rrentiatrd into 

 - iMirlionic cells, they come to lie deeper and deeper at the bottom 

 of anterior and posterior lwjiti"Hnnl j'urruu's (c and <//). Finally, 

 the completely formed spinal cord is composed of lar^r lateral halves, 

 which are separated from each other by deep anterior and po>turior 

 longitudinal fissures, being united only d, cp down by a thin trans- 

 verse bridge. Tlu- latin- i> d iiv 1 from the roof- and flooi>p! 

 which have been retarded in their growth, and encloses in its middle 

 the central canal, which has also remained small. 



etc 



Fig. 233. Cross section through the spinal cord of an embryo 

 Chick of seven days, after BAI.KOUR. 



pew, Posterior white column ; Uic, lateral white column ; 

 acw, anterior white column ; c, dorsal tissue filling \\\< the 

 l.huo where the dorsal fissure will be formed ; pc, \ 

 horn of the pi-ay substance ; oc, anterior horn ; ep, epithelial 

 cells ; age, anterior gray commissure ; pf, posterior [dorsal] 

 f the spinal canal ; 57 c, antoriur [ventral] part of the 

 spinal canal ; a/, anterior fissure. 



