232 STUDENTS HISTOLOGY 



of translucent, unstained white substance of Schwann. (These 

 are medullated fibers. In the spinal cord a neurilemma is wanting 

 for these fibers. With the Weigert-Pal method the medullary 

 sheaths are stained black and their course is easily traced.) 



(d) The small deeply haematoxylin- stained cells of the neuroglia. 



(e) The neuroglia-substance, finely granular or fibrillated, be- 

 tween the nerve -fibers. (/) The spider cells (Deiter's) of the 

 neuroglia. (These are not numerous, but easily found near the 

 periphery.) (g) The longitudinal nerve-fibers passing from the 

 anterior gray corau to form the anterior root of a spinal nerve. 

 (h) The different size of the nerve-fibers in different areas of 

 the section. Note the small fibers of the postero- internal column. 

 With certain exceptions, the larger fibers belong to motor tracts 

 and the smaller fibers to sensory tracts, (i) The blood-vessels. 

 (These vessels are largely confined to the fibrous septa, which 

 pass in from the pia.) 



5. The gray substance, (a) The central canal. (The canal 

 is lined with columnar ciliated cells in a single layer. The cilia are 

 rarely demonstrable in the human cord, except in children. The 

 central canal in adults is often partly occluded. Observe the clear, 

 homogeneous ground-substance, substantia gelatinpsa centralis. 

 Compare it with a similar mass covering the posterior horn, the 

 substantia gelatinosa Rolandi.) (&) The ground - substance. 

 (This consists, first, of exceedingly minute fibers, formed by the 

 repeated subdivision of the axis-cylinders the primitive fibrillae ; 

 second, of the delicate neuroglia-fibers. It is usually difficult 

 in a section to differentiate between the two. The details can only 

 be made out in preparations stained with silver by Golgi's method.) 

 (c) Large ganglion-cells. (In the anterior horn. The straight, 

 unbranching axis -.cylinder process can frequently be distinguished. 

 Note the large, shining nucleus and the deeply stained nucleolus. 

 These cells are frequently deeply pigmented. They may be divided 

 into two or three separate groups.) (d) Small ganglion-cells. 

 (Best seen in the posterior horn. In the dorsal cord a collection of 

 medium sized cells appears at the point where the gray commis- 

 sure joins the posterior horn, the column of Lockhart Clarke.) 

 (e) The lateral horn also contains small ganglion -cells. Occa- 

 sional outlying ganglion -cells appear in the white matter of the 

 antero-lateral and posterior columns. (/) Pericellular lymph- 

 spaces. '(Observed as a somewhat clear space around the ganglion- 

 cells.) (g) Blood-vessels. (These are much more numerous here 



