196 THE TISSUE OF THE ORGANIC MUSCLES, BY J. ARNOLD. 



network of pale fibres, just described, lies immediately upon 

 or beneath the muscular laminae, embraces the muscular bundles, 

 and probably intercommunicates freely with thefibres proceeding 

 from the fundamental plexus to form an intermediate plexus (fig. 

 33, 6). In the larger muscular fasciculi, portions of the inter- 

 mediate plexus are sometimes found within the layers ; but in 

 general the arrangement above described is that which obtains. 

 Fine fibres are given off from the intermediate plexus, which 

 penetrate between the muscular fibres, and at the points of 

 division still present nuclear enlargements, though these are 

 subsequently absent, the fibres at the same time becoming 

 rapidly attenuated (fig. 33, a). After they have undergone re- 

 peated division, they appear as fine, cylindrical, dark filaments, 

 of from 0-0003 to 0'0005 millimeters in diameter. These con- 

 tain, both in their course and at their points of division, dark 

 granules of round > elliptical, or polygonal form, which, by their 

 somewhat larger size (O'OOl to O'OOIS millimeters) and brighter 

 appearance, serve to indicate the course of the fibres (fig. 33, 

 a and &). They are tolerably distinct in preparations moistened 

 with serum; but, as has already been stated in the description 

 of the connecting substance, the delicate plexus formed by the 

 fibres is not very perceptible without the addition of other 

 reagents. The delicate fibres bearing nuclei, which have just 

 been described, unite with one another to form very delicate 

 networks, which traverse the connecting substance occupying 

 the interstices of the muscular fibres, and are seen winding 

 round the fibres in the form of delicate dark lines, interrupted 

 with nuclear enlargements, and constitute the intra-muscular 

 plexus. Transverse sections of frozen portions of muscle treated 

 with serum and chloride of gold permit these fine nuclei-bearing 

 fibres, with their relations to the connecting substance on the 

 one hand, and with the muscular fibres on the other, to be rea- 

 dily perceived (fig. 33, c). From the intra-muscular plexus, 

 and chiefly in the vicinity of the spindle-like enlargements of 

 the muscular fibres, dark peculiarly stiff filaments proceed, 

 having a diameter of 0'00015 to 0'0002 millimeters. These 

 penetrate into the interior of the fibres, and extend towards the 

 nucleus. Several of these filaments, or one only, in accordance 

 with the number of granules in the nucleus, may penetrate 



