THE FIBER TRACTS 



619 



rays, as was mentioned above. Between the fiber columns the dendronic 

 network is known as the interradial felt work; peripheral to where the 



fiber rays begin, this dendronic network _^ o 



forms the supraradial feltwork. At about ti| \ 



the middle of the large pyramidal cell I ,'**** 

 layer, abundant horizontal dendrons pro- 't/^ ; 

 duce a distinct broad band, the outer / 

 stripe of Baillarger. Between the large | 

 pyramidal cell layer and the outer poly- #./;'' 

 morphic cell layer, a similar but narrower 

 band is known as the inner stripe of Bail- \ ..VV,;'.', , ,;' 

 larger. These stripes are most pro- 

 nounced in the visual areas as was said 

 above. Another band of similar nature 

 at about the outer limit of the small 

 pyramidal cell layer forms the stripe of 

 Bechterew. Beneath the peripheral neu- 

 rogliar marginal velum the dendrons of 

 the pyramidal cells branch and form thus 

 a band of horizontal fibers, the tangen- 

 tial fiber layer or molecular fiber layer. 

 These fiber bands are conspicuous only in 

 specimens prepared with the Weigert 

 technic. Both cortex and medulla con- 

 tain abundant neuroglia cells. Those 

 contributing almost exclusively to the 

 marginal velum are fusiform elements 

 with lateral tufts of short horizontal 



fibers, and an expanding tuft of delicate fibers passing to the inner 

 border of the small pyramidal cell layer. The neurogliar elements of 

 the medulla are mostly of the long-rayed type. 



FIG. 534. HUMAN CORTEX CER- 

 EBRI, OLFACTORY REGION. 



a, tangential fiber layer; 6, 

 white matter of the medulla. 

 Nissl's stain. Moderately mag- 

 nified. (After Schlapp.) 



THE MENINGES AND BLOOD SUPPLY 



The brain and spinal cord are enveloped by the meninges, which 

 include three fairly distinct membranes, the dura mater, arachnoid, and 

 pia mater, and two cavities filled with lymph or a lymph-like fluid; 

 by this arrangement the cerebrospinal axis is, as it were, sruspended 

 in fluid, and is everywhere surrounded by a watery cushion. 



