I 28 HOW TO WORK 



may lie demonstrated, but this is not terminal. The finest fibrils 

 have often been traced for some distance and then lost. Thus some 

 have been led to conclude that they became lost in other tissues 

 or that they ended in the connective tissue ! I have shown that in 

 all cases they lose their dark bordered character, and are con- 

 tinued as a pale fibre for a long distance beyond this point, and at 

 last form with the prolongations from other fibres a very intimate 

 interlacement, plexus, or network, which is arranged in all cases 

 upon the same type but differs in complexity, extent, and relations 

 in the various terminal nerve organs. In investigating the mode of 

 termination of nerve fibres, the papillae of the tongue of many of the 

 lower animals, especially of the frog may be selected. 



The general distribution of the nerves beneath the skin, may be 

 well seen in the ear of the mouse, after the thin skin covering 

 it has been carefully dissected off. In the dura mater and other 

 fibrous membranes, I have seen many individual nerve fibres arranged 

 so as to form with others a coarse network, and a single fibre may 

 often be traced for a very long distance. 



The dark-bordered fibres often divide at the point where a 

 bundle diverges from the trunk one of the subdivisions passing 

 on in the trunk, while another pursues a different and sometimes 

 opposite direction in the bundle which leaves the trunk, and 

 each of these again divides and subdivides further on. The fibres 

 in these localities frequently leave their companions and pass a short 

 distance with others, so that a network is in this manner formed 

 upon the surface of the dura mater for instance and other mem- 

 branes, and immediately beneath the skin. The mesentery of the 

 mouse is a very good membranous texture in which to study the 

 distribution of nerves in a mammalian animal. Beautiful prepa- 

 rations showing the distribution of sensitive nerves may be obtained 

 from the snout of the pig, mole, and other animals. At the free edge 

 of the third eyelid of the frog is a most extensive plexus of fine dark- 

 bordered nerve fibres, which are arranged so as to form the most 

 beautiful network. 



The finest terminal plexuses of nerve fibres may be studied in the 

 proper tissue of the cornea, in the fibrous tissue in the abdominal 

 cavity of the frog, around arteries and veins, in the tongue, especially 

 the papillae of the hyla or green tree frog, in the mucous membrane 

 of the pharynx, in the lung and bladder of the same animal. The 

 relation of the nerves to the corneal corpuscles, and their prolonga- 

 tions should be carefully noted, pi. XXX, fig. 197. This investi- 

 gation, however, presents difficulties, and the student should not 

 attempt it until he has succeeded in making good specimens of other 



