384 ORIGINAL AETICLES. 



and longer and contain a larger number of vesicles. The general 

 arrangement of the grey substance has a striking resemblance to that 

 .of the lumbar region. 



In the spinal cord of Man the form of the grey substance differs 

 somewhat from that of Mammalia. Throughout, the posterior cornua 

 stand completely apart, and are joined only at their bases by a narrow 

 transverse commissure. Each posterior vesicular column occupies 

 the whole inner half of the cervix, and in appearance resembles that 

 of mammaha in the upper part of the lumbar enlargement. 



Dr. J. Traugott states that before and behind the central canal 

 in the cord of the frog, the grey matter consists of a gelatinous con- 

 nective tissue and differs notably from its characters in other parts — a 

 difference which is not found in the cord of man or other vertebrates. 

 In other parts the grey substance consists of the cellular and fibrous 

 elements. Its radiated character is due to the processes extending 

 from the epitheHum of the central canal, and which belong probably 

 to the connective tissue. The cells are large and small, the larger 

 are more abundant in the anterior horns, the smaller in the posterior 

 — both varieties of the nerve cells are met with scattered together 

 throughout the grey substance. 



The anterior commissure is formed of fibres passing across from 

 one side to the other and enclosing longitudinal fibres. The posterior 

 commissure is very slight and is even sometimes w^anting. The pos- 

 terior nerve-roots send processes to the anterior commissure. 



The fibres of both commissures are described by Schroeder van 

 der Kolk as consisting of white fibres not in immediate connection 

 with nerve roots, although probably indirectly connected with the 

 anterior roots by means of ganglionic filaments. (Plates X, XT . 

 figs. 4 and G, L and M.) 



The cells of the grey matter present great variation in form, size, 

 (fig. 1 c), and number of processes, depending much, as observed by 

 Dean, " on the direction of the plane of section with respect to the 

 situation of the cell." 



A distinction foimded on the size of the cells has been attempted, 

 dividing them into motor, sensitive, and sympathetic, but this is 

 a purely hypothetical and unfomided distinction, since there are 

 many cells, wiiich as Dean justly remarks, should be sensitive in the 

 anterior cornu, and motor in the posterior. 



Dean regards the cells as simply an enlargement of the axis 

 cylinder containing a granular substance and a nucleus. The cells 

 however possess such clearly distinctive characters as to justify their 

 being regarded as altogether independent structures giving off pro- 

 longations of their outer membrane. 



Dean defines the distinctive characters of grey and white matter, 



or vesicular and fibrous, as consisting in the presence of true nerve 



cells in the grey or vesicular, v.hily they are absent in the white or 



fibrou^t substance. " The so-called cells of the wliite substance, de- 



.Bcribed by Stilling and others," Dean adds, " are nothing more than 



