SPINAL CORD 



231 



absence of a white commissure posteriorly, the posterior median 

 septum reaching the gray substance.) 



3. Subdivisions of the gray substance, (a) The central 

 canal. (Its size and shape vary a good deal at different levels.) 

 (b) The gray commissures, anterior and posterior, (c) The gray 

 columns, (d) The anterior gray cornua, broad and not reaching 

 the periphery of the cord section, (e) The posterior cornua, 

 narrow and passing completely out, posteriorly, to form the pos- 

 terior root of a spinal nerve. 



(H.) 



4. The white substance. (Select a field, e. g., in the anterior 



PIG. 150. SAME SPECIMEN AS SHOWN IN FIG. 149. MORE HIGHLY MAGNIFIED. 

 REGION OF ANTERIOR CORNU (X 350). 



A. Medullated filaments passing out from the gray substance to form the anterior root 

 of a spinal nerve. 



B. Ganglion-cells. 



C. Neuroglia-nuclei. 

 I). Blood-vessels. 



E. One of the transversely divided medullated fibers of the white substance, anterior to 

 the anterior gray cornu. The line leads to the neurilemma. 



F. White substance of Schwann of E. 



G. The axis-cylinder of E. 



median column, and observe the transversely divided nerves.) 

 (a) The nerves are not collected into funiculi, but each fiber 

 pursues an independent course, (b) The axis-cylinders, which 

 suggest cell-nuclei. (Note the great variation in size.) (c) Most 

 of the axis -cylinders surrounded by more or less concentric rings 



