33O PRACTICAL HISTOLOGY. [XXX. 



same grey complex, but they do not unite with fibres from adjoining 

 cells or with nerve-fibres. 



Type 2, or Sensory Type. Also multipolar, smaller cells, with no 

 axis-cylinder process. All the processes subdivide into finer pro- 

 cesses, lose their individuality, and pass in toto into the nervous 

 complex, or diffuse nervous network in all strata of the grey matter 

 of the cord. These cells are therefore connected only indirectly 

 with nerve-fibres, i.e., through the intervention of the grey nervous 

 network ; and it is only in this indirect way that they come into 

 relation with contact, not actual union with the branches of 

 axis-cylinders of the nerve-fibres of the posterior root. 



Arrangement of Nerve-Cells. In the grey matter of the anterior 

 cornu, the large multipolar nerve-cells cells of the anterior cornu 

 are arranged in groups varying in different parts of the cord. Many 

 of their axis-cylinder processes pass out as axis-cylinders into the 

 nerves of the anterior root on the same side of the cord. These 

 cells are in relation with the fibrillar nerve-endings of the fibres of 

 the pyramidal tracts, and also with the collateral fibres of the pos- 

 terior root-fibres. In the upper dorsal and lower cervical regions 

 is a group of nerve-cells intermedio-lateral tract lying well for- 

 ward in a projecting part of the grey matter known as the lateral 

 cornu (fig. 317, Til). In the middle of the crescent is the middle 

 cell group. At the base of the posterior cornu, on its inner aspect, 

 is a group of large cells best marked in the thoracic region 

 Clarke's column (figs. 318, 319, CO/). The axis-cylinder pro- 

 cesses of the cells of Clarke's column pass into and become the 

 nerve-fibres of the direct cerebellar tract (p. 331). The cells of the 

 posterior cornu are small, and for the most part isolated. 



Diffuse Nervous Grey Network. The network or complex of 

 nervous fibrils in the grey matter of the cord is formed by (i.) 

 the fibres and their branches of the 2nd type of nerve-cells (p. 330) ; 

 (2.) the fibrils and prolongations of the protoplasmic fibres of the 

 ist type; (3.) the lateral branches of the axis-cylinder processes of 

 the ist type ; (4.) the fibrils produced by the terminal arborisations of 

 the axis-cylinders entering the cord by the posterior roots. 



Thus it is evident that some nerve-fibres spring from the cord 

 directly from nerve-cells, and others indirectly from the nervous 

 complex in the grey matter. Thus they are different, both morpho- 

 logically and physiologically. 



By several lines of research- including the facts of development, 

 experimental and pathological evidence the anatomical columns of 

 the cord can be shown to be further subdivided. By these methods 

 it is found that the posterior column consists of a narrower internal 

 part, the postero-internal or postero-mesial column, or funiculus 

 gradlis or column of Goll, and an outer, postero-lateral tract or 



