1865.] Nerves in Striped Muscle. 239 



may consist of an exceedingly delicate, pale, and scarcely visible fibre, con- 

 nected with a nucleus. Such delicate fibres and nuclei are to be demon- 

 strated amongst the muscular fibres of these arteries, but in consequence 

 of not having been able to trace them continuously for any great distance, 

 I cannot assert that these are true nerves ; but no one has yet proved they 

 are not nerves, or has demonstrated their real nature. 



The nerves which supply the small arterial branches in the voluntary 

 muscles of the frog, come from the very same fibres which are distributed 

 to the muscles. I have seen a dark-bordered fibre divide into two branches, 

 one of which ramified upon an adjacent vessel, while the other was distri- 

 buted to the elementary fibres of the muscle. In my paper " On the Struc- 

 ture of the Papillae of the Frog's Tongue " these statements have been con- 

 firmed ; and in the figure to which I now point, nerves distributed to arteries 

 and to elementary muscular fibres of striped muscle are seen to be derived 

 from the same trunk of dark-bordered nerve-fibres. 



DISTRIBUTION OF NERVES TO STRIPED MUSCLE. 



Of the arrangement of dark-bordered fibres distributed to voluntary 

 muscle and other tissues. 



The plexiform arrangement of nerve-trunks and nerve-fibres is one which 

 is very general, and was known even to the older anatomists. It can be 

 demonstrated in many cases even by rough dissection. It exists not only 

 in the case of nerves distributed to rmiscle, but, as far as is known, to every 

 other tissue which receives a supply of nerves. Many of these networks 

 are very beautiful ; and the arrangement is illustrated by these figures, 

 which represent the bundles of dark-bordered nerve-fibres distributed re- 

 spectively to the diaphragm of the white mouse, the mylohyoid of the green 

 tree-frog, and the eyelid of the same animal. The fibres constituting the 

 bundles never run perfectly parallel with one another, nor can a separate 

 fibre usually be followed for any great distance. This arises from the fact 

 that the fibres frequently cross one another, and many seem to pursue a spiral 

 course. The spiral arrangement of nerve-fibres has been already described 

 in former communications. At an early period of development one fibre 

 may be seen coiled spirally round the other, as is well shown in this 

 drawing*. The rule seems to be universal that fibres on one side of a 

 trunk cross over and pursue their course on the opposite side. Those on 

 the lower part of a trunk soon pass to the upper part, and vice versd. 

 Instead of a nerve passing to its distribution by the shortest route, it 

 invariably seems to pursue a very circuitous course. The course of the 

 nerve-fibres in the optic commissure is not peculiar to this part of the 

 nervous system, but a similar arrangement is to be met with in all nerves. 

 When two trunks meet, as represented in this figure, fibres are found to 

 pursue the several courses represented by the lines. 



* See also my paper " On the Structure of the so-called Apolar, Unipolar, and Bipolar 

 Nerve-cells," Phil. Trans. 1863. 



