76 HAND-BOOK OF PHYSIOLOGY. 



(4.) In plexuses, as in the cornea, both sub-epithelial and also intra- 

 epithelial. 



(5.) In cells, as in the salivary glands.(p. 228, Vol. I.), and in the special 

 sense organs. To the latter, further allusion will be made in a future 

 chapter. 



(b.) Motory. (1.) In unstriped muscle, the nerves first of all form 

 a plexus, called the ground plexus (Arnold), corresponding to each group 

 of muscle bundles; the plexus is made by the anastomosis of the primitive 

 fibrils of the axis-cylinders. From the ground plexus, branches pass off. 



FIG. 311. Summit of a Pacinian corpuscle of the human finger, showing the endothelial mem- 

 branes lining the capsules. X 220. (Klein and Noble Smith.) 



and again anastomosing, form plexuses which correspond to each muscle 

 bundle, intermediary plexuses. From these plexuses branches consisting 

 of primitive fibrils pass in between the individual fibres and anastomose. 

 These fibrils either send off finer branches, or terminate themselves in the 

 nuclei of the muscle cells. 



(2.) In striped muscle the nerves end in the so-called "motorial end- 

 plates" having first formed, as in the case of unstriped fibres, ground 

 and intermediary plexuses. The nerves are, however, medullated, and 

 when a branch of the intermediary plexus passes to enter a muscle-fibre, 

 its primitive sheath becomes continuous with the sarcolemma, and the 

 axis-cylinder forms a network of its fibrils on the surface of the fibre. This 

 network lies embedded in a flattened granular mass containing nuclei of 

 several kinds; this is the nwtorial end-plate (Fig. 312). In batrachia, 

 besides end-plates, there is another way in which the nerves end in the 

 muscle-fibres, viz., by rounded extremities, to which oblong nuclei are 

 attached. 



