1124 



GENERAL ANATOMY OR HISTOLOGY. 



nerve-fibres, experimentally shown to be sensory in origin, terminate. These 

 neuro-muscular spindles vary in length from -$ to - of an inch and have a distinctly 

 fusiform appearance. The large medullated nerve-fibres passing to the end-organ 

 are from one to three or four in number ; entering the fibrous capsule they divide 

 several times, and, losing their medulla, ultimately end in naked axis-cylinders 

 encircling the intrafusal fibres by flattened expansions, or irregular ovoid or rounded 

 discs (Fig. 662). Neuro-muscular spindles have not yet been demonstrated in the 

 tongue or eye muscles. 



In the organs of special sense the nerves appear to terminate in cells which 

 belong to the epithelial class, and have received the name of sensory or nerve- 

 epithelium cells. This is not, however, the real state of the case ; the nerve-fibre 

 is in reality a process from the epithelial cell, and terminates by branching around 

 a ganglion-cell. The stimulus carried by it is continued onward by an axis- 

 cylinder, derived from the ganglion, to the brain. These nerve-epithelium cells 

 must therefore be regarded as modified forms of nerve-cells. They will be 

 more particularly described in the sequel, in connection with the description of the 

 organs of special sense. * 



FIG. 653. Muscular fibres of Lacerta viridis with the terminations of nerves, a. Seen in profile. P.P. The nerve- 

 end-plates. s.s. The base of the plate, consisting of a granular mass with nuclei, b. The same as seen in look- 

 ing at a perfectly fresh fibre, the nervous ends being probably still excitable. (The forms of the variously- 

 divided plate can hardly be represented in a woodcut by sufficiently delicate and pale contours to reproduce 

 correctly what is seen in nature.) c. The same as seen two hours after death from poisoning by curare. 



Motor nerves are to be traced either into unstriped or striped muscular fibres. 

 In the unstriped or involuntary muscles the nerves are derived from the sympa- 

 thetic, and are composed mainly of the non-medullated fibres. Near their termi- 

 nation they divide into a number of branches, which communicate and form an 

 intimate plexus. At the junction of the branches small triangular nuclear bodies 

 (ganglion-cells) are situated. From these plexuses minute branches are given off, 

 which divide and break up into the ultimate fibrillae of which the nerve is com- 

 posed. These fibrillse course between the involuntary muscle-cells, and, according 

 to Elischer, terminate on the surface of the cell, opposite the nucleus, in a minute 

 swelling. Arnold and Frankenhiiuser believed that these ultimate fibrillse pene- 

 trated the muscular cell and ended in the nucleus. More recent observation, 

 however, has tended to disprove this. 



In the striped or voluntary muscle, the nerves supplying the muscular fibres 

 are derived from the cerebro-spinal nerves, and are composed mainly of medullated 

 fibres. The nerve, after entering the sheath of the muscle, breaks up into fibres, 

 or bundles of fibres, which form plexuses, and gradually divide until, as a rule, 

 a single nerve-fibre enters a single muscular fibre. Sometimes, however, if 

 the muscular fibre is long, more than one nerve-fibre enters it. Within the 

 muscular fibre the nerve terminates in a special expansion, called by Kiihne, who- 

 first accurately described them, motorial end-plates (Fig. 663). * The nerve-fibre, 



1 They had, however, previously been noticed, though not accurately described, by Doyere, wha 

 named them " nerve-hillocks." 



