836 



THE NERVE SYSTEM 



OORSO-LATERAL. 

 GROUP 



INTERMEDIATE 

 GROUP 



VENTRO-LATERA 

 GROUP 



DORSO-MEOIAL 

 GROUP 



VENTRO-MEOIAL 

 GROUP 



DORSAL NUCLEUS 

 (CLARKE) 



INTERMEDIATE 

 GROUP 



average diameter than those 

 of the white column; (3 

 nerve cells of various shape; 

 and sizes, with few or man^ 

 processes; (4) bloodvessels 

 lymphatic channels, anc 

 connective tissue. 



The nerve fibres of the 

 gray substance of the pos 

 terior horn are for the mosi 

 part composed of a dense 

 interlacement of minute 

 fibrils, intermingled witt 

 nerves of a larger size. Thi: 

 interlacement is formec 

 partly by the axones anc 

 dendrites of the cells of the 

 gray substance, and partly 

 by fibres which enter the 

 gray substance and whicl 

 come from various sources. 

 The nerve cells of the grai 

 substance are collected inte 

 groups (nidi or nuclei) a; 

 seen on transverse section 

 but they really form column; 

 of cells placed longitudinally 

 or else they are found scat 

 tered throughout the whol< 

 of the grav substance (Fig 

 609). 



In the ventral horn foui 

 main groups of cells may be 

 distinguished which are no 

 wholly represented, how 

 ever, in all regions of the 

 cord: (1) A ventral group o 

 cells, separable in the cervi 

 cal and lumbar regions inte 

 ventromedial and ventro- 

 lateral sub-groups; (2) s 

 dorsomedial group, situated 

 in the cervix of the ventral 

 horn, usually demonstrable 

 in the thoracic portion as 

 well as a few contiguous 

 cervical and lumbar seg- 

 ments; (3) a lateral group, 

 separable in the lower cer- 

 vical and lumbar regions 

 into ventrolateral and dorsolateral sub-groups, and supplying the muscles of the 

 extremities; (4) a central group of cells in the lumbar and sacral regions. 



In the lateral horn, which is most prominent in the thoracic and upper cervical 

 segments, lies an intermediate group of cells, a long, slender column which is 

 nearly restricted to the thoracic portion of the cord, but is seen to reappear in the 



DO RSO- LATERAL 



GROUP 



VENTRO-LATERAL 

 GROUPS 



VENTRO-MEDIAL 

 GROUP 



INTERMEDIATE 

 GROUP 



FIG. 609. Trans-sections of the spinal cord at different levels to show 

 the topographical arrangement of the principal cell groups. 





