346 



ENDINGS OF SENSORY NERVES. 



these terminations of the nerves are destined to fulfil. It is very probable, however, that the 

 series of concentric endothelial membranes with interposed fluid is an arrangement for con- 

 verting the effect of mechanical traction into fluid pressure upon the nerve, so that tension and 

 traction of the tissue in which the corpuscle is placed, may affect the axis-cylinder in the same 

 manner as ordinary pressure. 



Little also is known as to their development, except that when first visible they appear in 

 the form of small agglomerations of cells amongst which the termination of a nerve-fibre 

 becomes lost to view. 



Other modes of ending of sensory nerves. Instead of ending in the special 

 terminal corpuscles of different kinds which have been described in the preceding 

 pages, many sensory nerves, as before stated, terminate in the form of fine ramifica- 



Fig. 407. DISTRIBUTION OP NERVES IN A PORTION OP THE CORNEA OP THE RABBIT. (Ranvier. ) 



The nerves are stained with chloride of gold, p, larger plexus of non-medullated fibres, made up of 

 numerous fine fibrils ; a, a, smaller fibres derived from them, and themselves giving off still smaller 

 branches ; h, varicose fibrils ; t, junctional branches of the larger plexus. 



tions of the axis-cylinder, which pass between the elements of the tissue to which 

 the nerves are distributed, and may either simply come in contact with them, or, it 

 is believed, may in some cases form an actual connection with the cells. As they 

 approach their termination the sensory nerve-fibres, which are generally medullated, 

 divide dichotomously again and again, retaining after all the earlier divisions 

 both the medullary sheath and the primitive sheath, and being accompanied by 

 a prolongation of the sheath of Henle. Lower down this last-named sheath 

 becomes lost, and a short distance further on the medullary sheath also dis- 

 appears, the nerves being continued as pale fibres enclosed only by the nucleated 

 sheath of Schwann. Within this it can distinctly be seen in preparations stained 

 with chloride of gold, that the axis-cylinder is made up of fine varicose fibrils 

 (fig. 407). At every division of the nerve some of these fibrils pass into each 

 branch, and where, as often happens, the branches unite with one another so as to 

 form a subterminal plexus, some of the fibrils pass across from one branch to 

 another. By the time the terminal ramification is reached many of the branches 

 may consist of only one or two ultimate fibrils (h). It is generally found that the 

 sheath of Schwann has ceased long before this condition i? arrived at, although 

 nuclei apparently like those of that sheath may often be still seen here and there 

 upon the branches, especially at the points of bifurcation. Finally the branches of 

 the nerve, thus reduced to the condition of ultimate fibrils, often varicose, pass 

 between the tissue elements, and may there form an actual network by joining one 



