THE NERVOUS SYSTEM 547 



carine area (visual, fibres from lateral geniculate body), the trans- 

 verse temporal gyri of Heschl (auditory, fibres from medial geniculate 

 body), and the pre- and postcentral areas (postcentral only, according 

 to some authorities, area of general sensation from body and head, 

 fibres from ventrolateral thalamic nuclei). (Fig. 365.) 



The medullated fibres of the cortex consist of radially, obliquely, 

 and tangentially running fibres. The radial fibres enter the cortex 

 from the white matter in bundles known as the radiations of Meynert 

 which extend a variable distance toward the periphery, diminishing 

 until they end usually in the third layer. They consist mainly of the 

 axones of the adjoining cells passing to the white matter. Their 

 fibres are of varying caUbre, the coarsest originating from the largest 

 cells. The oblique fibres form a dense plexus of coarse and fine fibres 

 between the radial fibres, the interradiary plexus. Toward the 

 surface (in the second and third cell layers) they form a delicate plexus 

 of fine fibres. This latter plexus lies principally superficial to the 

 radiations of Meynert and is the supraradiary plexus. A denser 

 aggregation of irregular fibres constitute the line or stria of Baillarger 

 located in the layer of superficial large pyramids. It is probable that 

 this represents a layer especially rich in terminals of fibres from the 

 white matter. Other striae are also described. Besides represent- 

 ing the terminals of fibres from the white matter the oblique fibres 

 in general are also composed of medullated collaterals of axones of 

 pyramids and possibly arborizations of short axone cells. A few 

 coarser fibres ascending to the molecular layer are ascending fibres 

 from Martinotti cells. The deep tangential fibres, most marked on 

 the sides of the convolutions and in the sulci, are considered short 

 association fibres belonging to the fibrie propriae of Meynert. In 

 the molecular layer are the superficial tangential fibres consisting of 

 the axones of the horizontal cells and the terminals of the axones 

 of Martinotti cells. (Figs. 362 and 364.) 



The cortex is divided into various areas by various investigators, 

 the areas being distinguished {a) by the time of medullation (myelo- 

 genetic method of Flechsig), {b) by the number and arrangement of 

 the medullated fibres (myeloarchitecture), especially the number, 

 thickness, and distinctness of the striae, such as that of Baillarger, 

 formed by them, and (c) by the number and arrangement of the cells 

 (cytoarchitecture). Many such areas have been thus distinguished 

 by different investigators with results agreeing in many respects but 

 differing in others. The areas most clearly defined and concerning 



