358 THE SPINAL CORD, BY J. GERLACH. 



nuclei (fig. 227, c) surrounded by a thin zone of protoplasm, 

 which become more numerous with advancing age, and can only 

 be regarded as destined to replace the epithelial cells. Beneath 

 the layer of finely granular substance is an extremely close 

 plexus of fine fibres, in which also cellular elements are here 

 and there scattered (fig. 227, a). I consider this tissue also to 

 belong to the class of connective tissues, and to differ from the 

 neuroglia elsewhere so abundant in the grey substance, only in 

 the circumstance that the plexiform fibres already alluded to as 

 being probably of an elastic nature (?), are present in consider- 

 able quantities. This peculiar kind of neuroglia, the so-called 

 ependyma of the central canal, is surrounded on both sides and 

 behind by a plexus of delicate nerve fibres, which are often 

 brought beautifully into view in specimens prepared with 

 chloride of gold, and amongst which small nerve cells are 

 irregularly distributed. The meshes of this nervous plexus 

 are here wider than in other parts of the grey substance, 

 demonstrating the presence of a larger proportion of connective 

 tissue in this region. Behind the plexus of nerve fibres, and 

 immediately in front of the ependyma of the central canal, fine 

 fasciculi of nerve fibres run horizontally across the middle line, 

 connecting the two lateral halves of the spinal cord together, 

 and hence named the anterior and posterior commissural fibres 

 of the grey substance. The posterior, with the connective 

 tissue of which the septum posterius of the pia mater is con- 

 tinuous, are more numerous than the anterior; both can be 

 demonstrated with the greatest distinctness in specimens pre- 

 pared with chloride of gold. The results of the experimental 

 physiological researches of Brown-Se'quard render it probable 

 that the fine transverse fibres of the posterior grey commissure 

 are connected with portions of the brain destined for the 

 perception of sensory impressions, whilst the broad decussating 

 fibres of the anterior white commissure ascend to those portions 

 of the brain from which the impulses to voluntaiy movements 

 emanate. 



The two lateral portions of the grey substance of the spinal 

 cord constitute the anterior and posterior cornua, which are 

 not separated from one another by any sharply defined line of 

 demarcation. The description of these parts is consequently 





