1114 



GENERAL ANATOMY OR HISTOLOGY. 



not appear to be connected with the neuroglia-cells. They start from the epithelial 

 cells lining the ventricles of the brain and central canal of the spinal cord, and 

 pass through the nervous tissue, branching repeatedly to terminate in slight 

 enlargements on the pia mater. Thus, neuroglia is evidently a connective tissue 

 in function, but is not so in development; it is epiblastic in origin, whereas all 

 connective tissues are mesoblastic. 



Each nerve-cell consists of a finely fibrillated protoplasmic material, of a 

 reddish or yellowish-brown color, which occasionally presents patches of a deeper 





FIG. 646. Nerve-cells from the Gasserian 

 ganglion of the human subject, a. A globu- 

 lar one with defined border. 6. Its nucleus. 

 c. Its nucleolus. d. Caudate cell. e. Elong- 

 ated cell with two groups of pigment-par- 

 ticles. /. Cell surrounded by its sheath or 

 capsule of nucleated particles, g. The same, 

 the sheath only being in focus. Magnified 

 300 diameters. 



FIG. 647. Nerve-cells from the inner part of the 

 gray matter of the convolutions of the human brain. 

 Magnified 350 times. Nerve-cells : a. Larger, b. Smaller, 

 c. Nerve-fibre with axis-cylinder. 



'heath of 

 cell body. 



Nucleus. 



Cell protoplasm. 



Axon. 

 Myelin sheath. 



FIG. 648. Bipolar nerve-cell from the spinal gan- 

 glion of the pike. (After Kolliker.) 



4 N 



FIG. 649. Motor nerve-cell from ventral horn 

 of spinal cord of rabbit. (After Nissl.) The 

 angular and spindle-shaped Nissl bodies are 

 well shown. 



tint, caused by the aggregation of pigment-granules at one side of the nucleus, 

 as in the substantia nigra and locus coeruleus. The protoplasm also sometimes 

 contains peculiar angular granules, which stain deeply with basic dyes, such as 

 methylene-blue ; these are known as Nissl' s granules (Fig. 649). The nucleus is, 

 as a rule, a large, well-defined, round, vesicular body, often presenting an intra- 

 nuclear network, and containing a nucleolus which is peculiarly clear and 



