

THE MEDULLA SPINALIS OR SPINAL CORD 



763 



spinalis, and its apex directed toward the posterior gray commissure. It increases 

 in size from below upward, and consists of long thin fibers \vhich are derived from 

 the posterior nerve roots, and ascend as far as the medulla oblongata, where they 

 end in the nucleus gracilis. 



The fasciculus cuneatus (tract of Burdach) is triangular on transverse section, 

 and lies between the fasciculus gracilis and the posterior column, its base corre- 

 sponding with the surface of the medulla spinalis. Its fibers, larger than those of 



First 



thoracic 



nerve 



Descending comma fasciculus 



Dorsal peripheral band 



\& 



3. 



.Posterior 

 column 



Oval area of Flechsig. 



Posterior 

 column 



Triangular fasciculus 



FIG. 673. Formation of the fasciculus gracilis. Medulla 

 pinalia viewed from behind. To the left, the fasciculus 

 gracilis is shaded. To the right, the drawing shows that 

 the fasciculus gracilis is formed by the long fibers of the 

 posterior roots, and that in this tract the sacral nerves 

 lie next the median plane, the lumbar to their lateral 

 side, and the thoracic still more laterally. (Poirier.) 



Posterior 

 column 



FIG. 674. Descending fibers in the posterior 

 funiculi, shown at different levels. A. In the conus 

 medullaris. B. In the lumbar region. C. In the 

 lower thoracic region. D. In the upper thoracic 

 region. (After Testut.) 





the fasciculus gracilis, are mostly derived from the same source, viz., the posterior 

 nerve roots. Some ascend for only a short distance in the tract, and, entering 

 the gray matter, come into close relationship with the cells of the dorsal nucleus; 

 while others can be traced as far as the medulla oblongata, where they end in the 

 gracile and cuneate nuclei. 



The fasciculus gracilis and fasciculus cuneatus conduct (1) impulses of conscious 

 muscle sense, neurons of the second order from the nucleus gracilis and nucleus 

 cuneatus, pass in the median lemniscus to the thalamus and neurons of the third 



