t THE SPINAL CORD 87 



nective tissue from the pia and by the subpial neuroglia. It has been generally 

 supposed that the white fascicles of the cord were composed almost exclusively 

 of myelinated fibers; and it is true that these, partly because of their size, are 

 the most conspicuous elements. In cross-sections stained by the Weigert 

 method the myelin sheaths alone are stained; and since the fibers are cut at 

 right angles to their long axes, they appear as rings. Cajal (1909) has shown 

 that there are also great numbers of unmyelinated fibers in the longitudinal 

 fascicles of the cord (Fig. 62). The different fascicles differ not only in the size 

 of their myelinated fibers but also in the proportion of unmyelinated fibers 

 which they contain. The fasciculus dorsolateralis or tract of Lissauer (Fig. 63) 

 contains fine myelinated fibers with great numbers of unmyelinated axons. 



Fig. 63. From a cross-section of the spinal cord of the cat; a narrow strip extending across 

 the apex of the posterior gray column: a, Fasciculus cuneatus; b, fasciculus dorsolateralis (Lis- 

 sauer) ; c, dorsal spinocerebellar tract. The unmyelinated fibers appear as black dots. Pyridin- 

 silver method. 



Close to it lies the dorsal spinocerebellar tract which is composed almost ex- 

 clusively of large myelinated fibers. 



Gray Substance. The gray matter is composed of nerve-cells, including 

 their dendrites, and of unmyelinated axons and smaller numbers of myelinated 

 fibers all supported by a neuroglia framework and richly supplied with capil- 

 lary blood-vessels. The axons of the cells of Golgi's Type I are very long and 

 run out into the white substance or into the ventral roots. Those of the cells 

 of his Type II are short and end within the gray matter. In addition, great 

 numbers of collaterals from the dorsal root fibers and from the longitudinal 

 fibers of the cord, as well as terminal branches of these fibers, enter the gray 

 substance and ramify extensively within it, entering into synaptic relations 

 with the neurons which it contains. The branches of the myelinated fibers 

 soon lose their sheaths, and it is this relative scarcity of myelin which gives to 



