44 NERVOUS SYSTEM. 



Bidder, etc.). They consider it composed of a connective 

 mesh work (neuroglia) formed of trabeculae which may be com- 

 pared with the meshes of a sponge, and in certain places it 

 may even be condensed ; as, for instance, 1st, in the periphery 

 where it forms a cortical envelope ; 2d, around the central 

 canal of the spinal cord (periependymal nucleus) (see also, 

 Virchow, op. cit. p. 312) ; 3d, upon the two sides which 

 limit the posterior median fissure (septum posticum of Goll) ; 

 4th, around the posterior horns, where it forms the gelatinous 

 substance of Rolando, so well studied by Luys. 1 The essen- 

 tial part of this tissue in pathological neoplasms (new for- 

 mations) explains the importance attached to its study. 



With regard to the course of the nerve fibres in the spinal 

 cord, we have already insisted in this connection (vide p. 34) 

 that the spinal cord is principally a commissure between the 

 encephalon and the peripheral nerves, and indeed vivisec- 

 tions, and especially the study of degenerations in the spinnl 

 cord after section performed experimentally, or after patho- 

 logical alterations, have proved : 1st, that the posterior roots 

 are almost immediately lost sight of in the posterior horns of 

 the gray substance, some by their horizontal course, others 

 in an oblique course more or. less upwards or even down- 

 wards; some globules of the posterior horn start off then 

 from fibres which mount in the posterior columns even to the 

 floor of the fourth ventricle, and perhaps some may extend 

 even as far as the encephalon (L. Turck). The rest of the 

 posterior columns is formed of commissural fibres which 

 unite one region of the posterior horns to another of those 

 horns situated either above or below. 2d. The anterior roots 

 start from the anterior horns* and traverse almost in a hori- 

 zontal direction the white antero-lateral fasciculus ; this fas- 

 ciculus is formed of fibres coming from the corpus striatum 

 in the anterior horns, and by some vertical commissures from 

 one portion of these horns to another situated either above or 

 below. (Fig. 12.) 



The excitability of these fasciculi of the spinal cord forms 

 a problem difficult of solution, and upon which physiologists 

 are far from agreement. 1st. The antero-lateral column is 

 considered inexcitable by most physiologists ; however, Lon- 

 get has often obtained movements by the application of 



1 J. Luys. " Recherches sur le Systeme Nerveux Cerebro- 

 spinal." Paris, 1865. Luys considers that this substance is 

 formed of nerve elements, and not of connective tissue. 



