60 University of California Piihlioations in Anatomy [^01.. 2 



In general it can be said that the number of the intracortical 

 terminal somatic sensory fibers gradually decreases from the bottom of 

 the central sulcus, where it is the greatest, towards the limits of both 

 the precentral-front-al half as well as of the postcentral-parietal half 

 of the common somato-sensory region. (Compare CA in figs. 26, 27 

 with CP and PS in figs. 29, 30, 34, 36, 37 of Experiment I ; i^^ and 

 CA in figs. 44, 45 with CP and PS in figs. 50-53 of Experiment 

 II; and PS in figs. 66-69 of Experiment III.) The same gradual 

 decrease was observed toward the Sylvian fissure and toward the 

 cingular sulcus (for example figs. 46-49). Near the boundaries 

 of the common somato-sensory region of the hemisphere, the widest 

 extent of which is demonstrated in Experiment II (fig. 2), the number 

 of the intracortical sensory fibers becomes gradually so very much 

 reduced as to be represented by a few scattered, fine, or medium sized 

 fibers to be found now and then. Thus various cortical areas of the 

 common somato-sensory region show wide differences in respect to the 

 wealth of the afferent fibers. An attempt has been made to demon- 

 strate this by differential shading of the areas in the accompanying 

 illustrations (figs. 1, 2, 3, 6, 24). The diagrams, however, do not 

 fully portray the actual conditions for they do not show adequately 

 the gradual decrease of fibers. Differential shading is intended only 

 to show the approximate abundance of fibers of the several zones: 

 (a) of the richly supplied areas in the sulcus centralis and in its 

 neighborhood, corresponding with Brodmann's areas 1, 2, 3, and 4, 

 which contain from very numerous fibers (area 3, the narrow deeply 

 shaded area on both sides of the sulcus centralis in the accompanying 

 figures in reality buried in the sulcus itself) to fairly numerous ones 

 (double shaded areas on both sides of the sulcus centralis in these 

 figures corresponding with areas 1, 2, and 4 of Brodmann), while 

 (&) the remaining parietal and frontal areas (lightly shaded areas in 

 the accompanying figures), corresponding with Brodmann's areas 5, 

 7, and 6, which form a peripheral belt or zone of the common somato- 

 sensory region, contain from rare, loose fiber bundles to a few scat- 

 tered individual fibers. Although the transition from one area to its 

 contiguous neighbor, as has been said, is a fairly gradual one, the 

 limits of differently shaded areas as given in the accompanying dia- 

 grams based on repeated minute examination of the three continuous 

 series, do roughly indicate the richly and poorly supplied areas. On 

 the other hand, it is fairly certain that the remaining regions of the 

 hemisphere left outside the shaded areas in figures 1, 2, 3, and 4, are 



