140 [June 19, 



those ramifying in the sheath of the nerves, may sometimes be 

 followed over six or more elementary muscular fibres, and form, with 

 other fine branches, networks, many of the meshes being as wide as 

 a muscular .fibre. 



7. Fine nerve-fibres with nuclei connected with them exist (not 

 unfrequently to the number of four or five) in the sheath of the 

 dark-bordered nerve-fibres near their distribution ; and some are also 

 found external to what appears to be the outline of the sheath. 

 Some of these result from the subdivision of a dark-bordered fibre. 



These fine fibres and their nuclei have been hitherto included 

 under the head of ' connective tissue.' 



8. The connective tissue around the elementary muscular fibres, 

 and in connexion with the nerve- fibres, is composed of 



a. Nuclei which might have taken part in the formation of 

 the nerve-fibres, but which have degenerated, and a low form 

 of fibrous tissue has alone been produced. 



b. Fibres and nuclei which were once active, and formed an 

 integral part of the nervous system, but which have grown old, 

 and have been replaced by new nuclei and fibres. 



c. The remains of altered and wasted vessels and nerve-fibres 

 distributed to them, and wasted muscular fibres themselves. 



9. The nerves distributed to the voluntary muscles of the frog do 

 not terminate in free ends, but there is reason for believing that 

 complete nervous circuits exist. In all cases the fibres resulting 

 from the division of the ordinary nerve-fibres are so fine that many 

 cannot be seen with a power magnifying less than 1 000 diameters, and 

 there is evidence of the existence of fibres which could only be demon- 

 strated by employing a much higher magnifying power. It is by 

 these very fine fibres alone, and their nuclei, that the tissues are 

 influenced. The ordinary nerve-fibres are only the cords which 

 connect this extensive peripheral system, which has been traced in 

 different tissues far beyond the point to which the dark-bordered 

 nerve-fibres can be followed, with the central organs of the nervous 

 system. 



10. The facts and conclusions above stated, with reference to the 

 distribution of nerve-fibres to the voluntary muscles of the frog, are 

 in accordance with the arrangement of the finest nerve-fibres demon- 

 strated in many other tissues of the same animal, and agree with 



