7 o 



CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES 



that each individual nerve fiber in the central nervous system gives off in its 

 course branches which pass out from it at right angles for a short distance, 

 and then may run in various directions. These branches are called collaterals. 

 They end in fine, brush-like terminations known as end-brushes, or in little 



FIG. 91. 



FIG. 92. 



FIG. 91. Nerve Cell with Short Axis-cylinder from the Posterior Horn of the Lumbar 

 Cord of a 0.55 cm. Embryo Calf. (After Van Gehuchten.) 



FIG. 92. Scheme of Lower Motor Neurone. The cell body, protoplasmic processes, 

 axone, collaterals, and terminal arborizations in muscle are all seen to be parts of a single 

 cell. and together constitute the neurone. (Barker.) c, Cytoplasm of cell body containing 

 chromophilic bodies, neurofibrils, and perifibrillar substance; n', nucleus; n, nucleolus; d, 

 dendrites; ah, axone hill free from chromophilic bodies; ax, axone; sf, side fibril (collateral); 

 m, medullary sheath; nR, node of Ranvier where side branch is given off; si, neurilemma 

 and incisures of Schmidt; m, striated muscle fiber; tel, motor end-plate. 



bulbous swellings which come in close contact with other nerve cells, 

 figures 83 and 90. 



In the nerve centers, that is, in the brain and spinal cord, the different 

 nerve fibers end just as the collaterals do, by splitting up into fine branches 

 which form the end-brushes. Collaterals of the nerve fibers and end-brushes 



