THE NERVOUS SYSTEM 



459 



the plexus in the gray and the adjoining white matter. In the ventral part of 

 the cord a similar interchange takes place, but here besides these fine fibres are 

 seen the coarse fibres of the ventral roots gathered from various parts of the 

 ventral horn to form bundles which leave the ventral side of the horn, pass through 

 the white matter and emerge as the ventral root fibres. The larger bundles of 

 fibres in the ventral horn separate the cell groups, but between individual cells 

 are seen numerous fine mcduUated fibres (principally terminals of fibres from the 

 white funiculi). Trace as far as possible the course of the fibres of the ventral 

 and dorsal white commissures. 



Finer Structures.' — Study with the high power the general histological struc- 

 ture of the gray and white matter. In the gray matter note (Cajal, Nissl, H.-E.), 

 besides the nerve cells and their processes, the neuroglia nuclei. Note also the 

 structure and size of the medullatcd nerve fibres (Weigert). In the white matter 



Fig. 321. — From Transverse Section of Elephant's Cord. (Hardesty.) Benda's 

 Neuroglia Stain, b, c, d and i. Four types of neuroglia cells; k, neuroglia fibre passing 

 through several neuroglia cells; /, leucocyte. 



note the appearance of the cross-cut medullated nerve fibres in Weigert, Cajal 

 and H.-E. preparations. With the neuroglia stains study carefully the neuroglia 

 cells and neuroglia fibres, including the neuroglia zone forming the margin of the 

 cord. (Fig. 321.) Note also the pia mater and the connective-tissue septa 

 (usually perivascular) entering the cord from the pia accompanied usually by a 

 denser aggregation of glia fibres. Note carefully the number of neuroglia nuclei 

 in some small field. Increase in neuroglia is characteristic of many pathological 

 conditions. Study the ependyma. (Weigert, Nissl, Cajal and glia stains). 



Study the internal structure of the nerve-cells of various sizes present, espe- 

 cially the amount and arrangement of the chromophilic substance (Nissl). The 

 smallest nerve cells of the cord have a limited amount of chromophilic substance, 

 often either in the form of perinuclear caps or small bodies near the periphery 



' It may sometimes be advantageous to have the high power study of the general 

 histological structure of the gray and white matter of the cord precede the study of the 

 architectural arrangements of the cord here placed first. 



