OF THE NERVOUS SYSTEM. 407 



cylinder alone; that is, all the secondary elements of its structure are 

 lost, and there remains only the essential conducting filament of the 



Fig. 138. 



DIVISION o* WERVE FIBRES, in a small branch from the subcutaneous muscle of a 



frog. (Kolliker.) 



axis cylinder. Lastly the nerve fibre, at the point of its final termina- 

 tion, is frequently brought into relation with cell-like bodies, which are 

 sometimes regarded as analogous in character to the nerve cells of the 

 gray substance in the nervous centres. 



The ultimate termination of the nerve fibres in the skin has been most 

 distinctly seen in the so-called " Pacinian bodies" and the " tactile cor- 

 puscles." The Pacinian bodies are ovoid-shaped masses from 1 to 4.5 

 millimetres in length, found in the subcutaneous connective tissue of the 

 hands and feet, and various other parts of the body, consisting of a 

 series of concentric laminae of connective tissue, with a central cavity, 

 inclosing a transparent, colorless, fluid or semifluid material. A single 

 ultimate nerve fibre penetrates the Pacinian body at one extremity, and 

 passes into its central cavity. At the point of entrance, the external 

 tubular sheath leaves the nerve fibre and becomes continuous with the 

 connective tissue laminae of the Pacinian body. The medullary layer 

 also disappears, and the nerve fibre, thus reduced to its axis cylinder, 

 runs longitudinally through the greater part of the central cavity and 

 terminates, toward its farther end, in either one or several slightly 

 rounded extremities. The "tactile corpuscles," found in the sensitive 

 papillae of the skin of the hands and feet, are similar in form to the 

 Pacinian bodies, but of much smaller size ; having an average length, 



