THE SPINAL CORD. 



713 



than in any other region of the cord. Toward the lower end of the cord the white 

 matter gradually ceases. The crescendo portions of the gray matter soon blend into 

 a single mass, which forms the only constituent of the extreme point of the cord. 



Minute Anatomy of the Cord. The cord consists of an outer part, composed 

 of medullated nerve-fibres, which is the white substance ; and of a central part, the 

 gray matter, both supported in a peculiar kind of tissue, called neuroglia. 



The neuroglia consists of a homogeneous transparent matrix, of a network of 

 very delicate fibrillae, and of small stellate or branched cells, the neuroglia-cells. 



In addition to forming a ground substance, in which the nerve-fibres, nerve- 

 cells, and blood-vessels are imbedded, a considerable accumulation of neuroglia 

 takes place in three situations (1) on the surface of the cord, beneath the pia 

 mater ; (2) around the central canal, the substantia gelatinosa centralis ; and 

 (3) as a cap over the extremity of the posterior horn, forming the substantia 

 cinerea gelatinosa. 



The white substance of the cord consists of medullated nerve-fibres, mostly 

 disposed longitudinally, with blood-vessels and neuroglia. When stained with 

 carmine it presents a very striking appearance on transverse section. It is seen 

 to be studded all over with minute dots, surrounded by a white area (Fig. 387). 

 This is due to the longitudinal medullated fibres seen on section. The dot is the 

 axis-cylinder, the white area the substance of Schwann. Externally, the neuroglia 

 forms a sheath closely investing the outer surface of the cord immediately beneath 

 the pia mater; from it numerous septa pass inward and separate the respective 

 bundles of fibres and extend between the individual nerve-fibres, acting as a 

 supporting medium, in which they are imbedded. 



There are, however, also oblique and transverse fibres in the white substance. 

 These principally consist of (1) the fibres of the white commissure ; (2) horizontal 

 or oblique fibres passing from the roots of the nerves into the gray matter ; and 

 (3) fibres leaving the gray matter and pursuing a longer or shorter horizontal course. 



Conducting Tracts. It is impossible to trace the course pf the nerve-fibres in 

 their passage through the cord ; 

 but the investigation of patho- 

 logical lesions has shown that 

 the white matter of the cord 

 consists of certain columns or 

 tracts of fibres ; for it has been 

 found that certain lesions are 

 strictly limited to certain well- 

 determined parts of the cord 

 without involving neighboring 

 regions. That these parts or 

 fasciculi correspond to so many 

 distinct anatomical systems, each 

 endowed with special functions, 

 seems abundantly proved by the 

 researches of Flechsig and others 

 on the development of the spinal 

 cord during the later periods of 

 utero-gestation and in the newly 

 born infant. By these researches 

 several tracts can be traced 

 along the greater part of the 

 cord and into or from the en- 

 cephalon. Thus (1) in the antero- 

 lateral column of the cord, on 

 either side of the anterior median 

 fissure, a portion of the column 

 may be divided off as the direct pyramidal tract (fasciculus of Turck). This tract 



FIG. 383. Columijs of the cord. 



