837 



\ 



CERVICAL 

 NUCLEUS 



DIRECT 



SPINOCCREBELLAR 

 TRACT 



DORSAL NUCLEUS 

 ~(CLARKE-S COLUMN) 



upper three cervical and in the third and fourth sacral segments. The axones 

 from these cells probably do not pass out with the ventral nerve roots, but rather 

 course within the cord to terminate at various levels on the same as well as on 

 the opposite side. A close connection with the sympathetic nerve system, and 

 with vasomotor and sweat-gland nerves, has been suggested. 



In the dorsal horn the most conspicuous group of cells is a columniform nucleus 

 commonly termed Clarke's column (nucleus dorsalis), which extends between the 

 seventh cervical and second (or third) lumbar segments of the cord. The cells 

 are large and the group presents an oval 

 outline in trans-sections, lying in the medial 

 part of the cervix of the dorsal horn. The 

 axones of these cells pass out of the gray 

 into the lateral column of the cord to form 

 the spinocerebellar tract, and convey tactile 

 impulses to the cerebellum. It is repre- 

 sented in other regions of the cord by scat- 

 tered cells which are aggregated to form 

 the cervical nucleus opposite the third cer- 

 vical nerve, and a sacral nucleus in the middle 

 and lower part of the sacral region. The 

 axones of these cells form the homolateral 

 direct cerebellar tract. 



The cells of the dorsal horn are not 

 grouped very definitely, and for the purposes 

 of description they are subdivided accord- 

 ing to their location. The cells vary much 

 in form and size and their branched axones 

 pass toward other regions within the gray 

 substance at various levels on the same or 

 on opposite sides, or via the ground bun- 

 dles. Many fibres of the dorsal nerve roots 

 are in relation with the dorsal horn cells. 



The various groups of cells enumerated 

 above are frequently demarcated from 

 neighboring groups by nerve fibre intervals, 

 which may be straight, curved, interlaced, or 

 loop-shaped. 



Through the gelatinosa Roland! (gliosa 

 cornualis) pass numerous fine fibrils, 

 chiefly the afferent dorsal nerve root fibres, 

 but in addition this peculiar, gelatinous, 



and semitranslucent substance contains numerous small, stellate cells; the region 

 is so densely filled with axones and collaterals, as well as neuroglia cells, that until 

 staining methods became sufficiently developed the importance of this substance 

 remained in dispute. In man the gelatinosa Rolandi shows convolutions feebly 

 imitating those of the olive, and its structure is analogous. Dorsad of the 

 gliosa lies the ultimate zone of the dorsal horn; this gray substance resembles 

 the spongiosa in its essential characters. 



The White Substance of the Cord (substantia alba). The white substance of the 

 cord, consisting chiefly of longitudinally disposed myelinic fibres, with blood- 

 vessels, neuroglia, and connective-tissue septa, forms a thick mantle which invests 

 the central gray column. When stained with carmine, a transverse section of 

 the white substance is seen to be studded all over with minute dots surrounded 

 by unstained circular areas. The dots are the transversely cut axones; the lighter 

 areas are the myelin sheaths. The mass of white substance is closely invested by 



V 



if: 



ACRAL 

 UCLEU8 



FIG. 610. Showing the dorsal nucleus (of 

 Clarke), and its cervical and sacral extensions 

 on one side, and the direct spinocerebellar tract 

 on the other. The fibres of the tract ascend on 

 the same side as the nucleus in which they 

 arise. 



