NERVE COLLATERALS 



69 



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 

 are chiefly found in the nervous centers. The nerve fibers of the peripheral 

 nerves end in the muscles, glands, or special sensory organs, such as the 

 eye and ear, each by its own special type of ending. Here, however, some 

 analogy to the end-brush can also be discovered. As the peripheral nerve 

 fibers approach their terminations, they lose their medullary sheath, and 

 consist then merely of an axis-cylinder and primitive sheath. They may 

 even lose the latter, and only the axis-cylinder be left. Finally, the axis- 

 cylinder breaks up into its elementary fibriHae, to end in various ways to 

 be described later. 



FIG. 91. 



FIG. 92. 



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

 an Embryo Calf, measuring 0.55 cm. (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, neuro- 

 fibrils, and perinbrillar 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 mus- 

 cle fiber; tel, motor end plate. 



