118 On muscular Motion. 



injecting the smaller branches of the lymphaedacts retro- 

 grade in an cedematous human leg, I saw, very distinctly, 

 three orifices of these vessels terminating in the angles of 

 the cells, into which the quicksilver trickled. The prepara- 

 tion is preserved, and a drawing of the appearance made at 

 the time. It was also proved, ~bv many experiments, that 

 neither the lymphasducts nor the veins have any valves in 

 their minute branches. 



The nerves of vohmtarv muscles separate from the same 

 bundles of fibrils with the nerves which are distributed iri 

 the skin, and other parts, for sensation ; but a greater pro- 

 portion of nerve is ap<}iropriated to the voluntary muscles 

 than to any other substaiices, the organs of the senses ex- 

 cepted. 



The nerves of volition all arise from the parts formed by 

 the junction of the two great masses of the brain, called 

 the cerebrum and cerebtUiim, and from the extension of 

 that substance throughout the canal of the vertebrae. An- 

 other class of muscles, which are not subject to the 

 ■will, are supplied by peculiar nerves ; they are n)uch 

 smaller, in proportion to the bulk of the parts on which 

 they are distributed, than those of the voluntary muscles ; 

 they contain less of the white opake medullary substance 

 than the other nerves, and unite their fibrils, forming nu- 

 merous anastomoses with all the other nerves of the body, 

 excepting those appropriated to the organs of the senses. 

 There are enlargements at several of these junctions, called 

 ganglions, and which are composed of a less proportion of 

 the medullary substance, and their texture is firmer than 

 that of ordinary nerves. 



The termmal extremities of nerves haveljeen usually con- 

 sidered of unlimited extension : by accurate dissection, how- 

 ever, and the aid of niagnifying-glasscs, theextreme fibrils 

 of nerves are easily traced as far as their sensible properties, 

 and their continuity extend. The fibrils cease to be sub- 

 divided, whilst perfectly visible to the naked eye, in the 

 voluntary muscles of large animals ; and the spaces they 

 occupy upon superficies where they seem to end, leave a 

 remarkable excess of parts unoccupied by those fibrils, 'ihe 

 extreme fibri's of nerves lose their opacity, the medullary 

 substance appears soft and transparent, the enveloping 

 membrane becomes pellucid, "and the whole fibril is desti- 

 tute of the tenacity necessary to preserve its own distinct- 

 ness; it seems to be diffused and mincrled with the sub- 

 stances in which it ends. Thus the ultimate terminations 

 of nerves for volition, and ordinary sensation, appear to be, 



in 



