clvi NERVOUS SYSTEM. 



An analogous arrangement is described by Axel Key~as discoverable in the fungi- 

 form papillae of the frog's tongue. Among non-ciliated columnar epithelium cells 

 are fusiform gustatory cells, having, like the olfactory cells, fine rod-like processes 

 reaching to the surface, and slender, varicose, central filaments, which seem to be 

 continuous with pale fibrils, into which the axis-cylinder of the gustatory nerve- 

 fibres finally divides ; and in such way that one axis-cylinder may be connected with 

 several cells. 



d. In epithelium. Hoyer believes he has seen fine, pale filaments continued from 

 the plexus of the cornea into the epithelium covering its anterior surface, where they 

 appeared to pass between the cells. Von Heusen de-scribes and figures exquisitely 

 fine filaments connected with the nucleoTi of epithelium cells on the tadpole's tail. 

 He finds evidence to satisfy him that their filaments are continued from the cutaneous 

 nerves, which he therefore conceives to run out into epithelium cells as their terminal 

 organs, and end in the nucleoli. 



e. In glands. The termination of nerves in secreting glands will be most conve- 

 niently given in the account of the structure of these organs. In the meantime it 

 may be stated that Pfliiger has traced nerve-fibres to the nuclei of the cells which line 

 the terminal saccules of the salivary glands. 



Termination of nerves in muscles : 



A. In plain or unstriped muscle. Dr. Beale, and, after him, Dr. Klebs, have 

 described the nerves of the muscular coat of the frog's bladder as finally distributed in 

 networks of pale fibres, with nuclei. The networks are at first coarser, with larger 

 grey fibres made up of coalesced fibrils (fibrillar fibres), and from these proceed finer 

 bundles and single fibrils, forming closer reticulations, constituting the intramuscular 

 plexus, which is disposed among the muscular fasciculi and fibre-cells. A more inti- 

 mate relation to the latter could not be traced with certainty, although Klebs met 

 with a single instance of a nerve-fibril entering a muscular fibre-cell. The nerves 

 distributed to the middle or muscular coat of the arteries are, according to Beale, dis- 

 posed in a similar plexiform manner ; and Julius Arnold has since found a terminal 

 pale nervous network of the same kind in the iris of the rabbit. 



B. In voluntary muscle, a. By plexuses. As mentioned in the account of the 

 muscular tissue, the nerves in the voluntary muscles form plexuses, of which the 

 branches grow finer and the meshes closer as they advance further into the tissue. 

 The individual fibres, while still associated in small bundles, undergo division (fig. 

 LXXXV), and at length single dark-bordered fibres pass off to the muscular fibres. 

 These nerve-fibres on approaching or reaching a muscular fibre divide still further. 

 As to their ulterior and final distribution, there is great divergence in the statements 

 of very able observers. Beale and Kb'lliker agree in opinion that the fibres lose their 

 dark borders and run further on as pale fibres, which do not penetrate the sarcolemma. 

 Dr. Beale describes the pale fibres, in the mouse and frog, as distributed in a fine 

 network, bearing nuclei, adhering to, but outside, the sarcolemma, and extending over 

 a great length of the muscular fibre. Kb'lliker, whose observations were made on the 

 frog, found the fibres apparently to terminate by free ends ; at the same time, having 

 seen, here and there, indications, although imperfect, of a fine network, such as he had 

 observed in the electric organ of the torpedo, he is not disposed to exclude the possi- 

 bility of such mode of termination. 



b. By terminal organs. Since the publication of Beale and Kblliker's observations, 

 a very different account has been given by Eouget namely, that the muscular nerves 

 end in peculiar terminal organs, which have been named the motorial end-plates, to 

 be seen on the muscular fibres, and his account has been in the main confirmed by 

 various contemporary observers, although some important authorities still hold to a 

 different view. The end-plates are described as small lamelliform objects, of an oval 

 or irregular, and often deeply indented outline ; their size varies from ^gg to ^ of 

 an inch, according to the size of the muscular fibre, of which the plate may embrace 

 one-third, or more, of the circumference. There is a question whether these organs are 

 situated without or within the sarcolemma. W. Krause, who adopts the former view, 

 describes the end-plate as consisting of a thin lamina of connective tissue, attached by its 

 oval or irregular border to the sarcolemma, with clear non-granular nuclei in it, and a 

 finely granular matter underneath, between it and the sarcolemma, in which the axis- 

 cylinder of the nerve-fibre ends, in form of one, or sometimes more, short pale fibres, with 

 free and swollen extremities; whilst the medullary sheath ceases, and the primitive sheath 



