

THE MEDULLA SPINALIS OR SPINAL CORD 



759 



Nerve Fasciculi. The longitudinal fibers are grouped into more or less definite 

 bundles or fasciculi. These are not recognizable from each other in the normal 

 state, and their existence has been determined by the following methods: (1) 

 A. Waller discovered that if a bundle of nerve fibers be cut, the portions of the 

 fibers which are separated from their cells rapidly degenerate and become atrophied, 

 while the cells and the parts of the fibers connected w r ith them undergo little alter- 

 ation. 1 This is known as Wallerian degeneration. Similarly, if a group of nerve 

 cells be destroyed, the fibers arising from them undergo degeneration. Thus, 

 if the motor cells of the cerebral cortex be destroyed, or if the fibers arising from 

 these cells be severed, a descending degeneration from the seat of injury takes 

 place in the fibers. In the same manner, if a spinal ganglion be destroyed, or the 

 fibers which pass from it into the medulla spinalis be cut, an ascending degenera- 

 tion will extend along these fibers. (2) Pathological changes, especially in man, 

 have given important information by causing ascending and descending degenera- 





Septomarginal fasciculus 

 pomma fasciculus 



'osterior proper fasciculus 



^Lissauer's fasciculus 



Lateral cerebrospinal 

 fasciculus 



Rubrospinal 

 fasciculus 

 (Monakow) 



Tectospinal ; 

 fasciculus 



Vestibulospindl 

 " fasciculus 



Anterior cerebrospinal fasciculus 



\ Sulcomarginal fasciculus 

 * Anterior proper fasciculus 

 FIG. 672. Diagram of the principal fasciculi of the spinal cord. 



tions. (3) By tracing the development of the nervous system, it has been observed 

 that at first the nerve fibers are merely naked axis-cylinders, and that they do not 

 all acquire their medullary sheaths at the same time; hence the fibers can be grouped 

 into different bundles according to the dates at which they receive their medullary 

 sheaths. (4) Various methods of staining nervous tissue are of great value in 

 tracing the course and mode of termination of the axis-cylinder processes. 



Fasciculi in the Anterior Funiculus. Descending Fasciculi. The anterior cerebro- 

 spinal (fasciculus cerebrospinalis anterior; direct pyramidal tract), which is usually 

 small, but varies inversely in size with the lateral cerebrospinal fasciculus. It 

 lies close to the anterior median fissure, and is present only in the upper part 

 of the medulla spinalis; gradually diminishing in size as it descends, it ends about 

 the middle of the thoracic region. It consists of descending fibers which arise 



1 Somewhat later a change, termed chromatolysis, takes place in the nerve cells, and consists of a breaking down and 

 an ultimate disappearance of the Nissl bodies. Further, the body of the cell is swollen, the nucleus displaced toward 

 the periphery, and the part of the axon still attached to the altered cell is diminished in size and somewhat atrophied. 

 Under favorable conditions the cell is capable of reassuming its normal appearance, and its axon jnay grow again. 



Fasciculus gracilis-,^ 



(GolL) 



Fasciculus cuneatus^ 

 (Burdach) 



Lateral proper 

 fasciculus 



.Dorsal 



spinocerebellar . j - t 

 fasciculus I i 

 (Flechsig) ggf 



Ventro 



spinocerebellar 



fasciculus 



(Gowers) 



Posterior 



spinothalamfc 



fasciculus 



Spinotectal ' 

 'fasciculus 



Anterior spinothalamic 

 fasciculus 



