80 THE NERVOUS SYSTEM 



appearance in the fresh condition and very difficult to stain by neurologic meth- 

 ods, which in sections has a A -shaped outline. It is known as the substantia 

 gelatinosa Rolandi. In the thoracic portion the posterior column, which is here 

 very slender, does not come so close to the surface; and in the lumbosacral seg- 

 ments it is much thicker (Figs. 56, 57). 



The anterior column is relatively short and thick and projects toward the 

 anterolateral sulcus. It contains the cells of origin of the fibers of the ventral 

 root. From its lateral aspect nearly opposite the gray commissure there pro- 

 jects a triangular mass, known as the lateral column (columna lateralis). This 

 is prominent in the thoracic and upper cervical segments; but it blends with 

 the expanded anterior column in the cervical and lumbar enlargements (Fig. 56). 



Posterior median sulcus and septum Posterior funiculus 



Substantia gelatinosa \ Dorsolateral fasciculus (Lissauer) 



Posterolateral sukus ^^^^^ Dorsal root 



BiBbU; Lateral funiculus 

 Apex oj posterior column 



Nucleus dorsalis 

 lateral column 



'! ^---^-- ^Central canal 

 Anterior white commissure ' ^iwKSB^H ^f^^r .... 



. . , .--' ----. y-^ Anterior funicmus 



Anterior column' ;~^--^_ . ,. ,. 



" Anterior median jissure 



Fig. 56. Section through the seventh thoracic segment of the spinal cord of a child. Pal-Weigert 



method. 



The reticular formation (formatio reticularis) , situated just lateral to the cer- 

 vix of the posterior column in the cervical region, is a mixture of gray and 

 white matter (Fig. 55). Here a network of gray matter extends into the white 

 substance, breaking it up into fine bundles of longitudinal fibers. The reticular 

 formation is most evident in the cervical region, but traces of it appear at other 

 levels. 



The gray commissure contains the central canal, and by it is divided into the 

 posterior commissure (commissura posterior) and the anterior gray commissure 

 (commissura anterior grisea). Ventral to the latter many medullated fibers 

 cross the midline, constituting the anterior white commissure. 



The cavity of the neural tube persists as the central canal, which lies in the 

 gray commissure throughout the entire length of the cord. The canal is so 

 small as to be barely visible to the naked eye. It is lined with ependymal 



