TISSUES OF THE BODY. 



325 



Fig. 312. Two narrow branching nerve fibres (a, b) from 

 the mesentery of the frog, surrounded with a thick 

 nucleated envelope. At 1, the trunks; at 2 and 3, the 

 branches. 



From this plexus are given off, in the first place, medullated nervous* 

 fibres, which assume, after a 

 longer or shorter course, the 

 form of pale longitudinally 

 striated bands of 0'0041- 

 0'0050 mm. in diameter, con- 

 taining at intervals nuclei of 

 the same dimensions. These 

 bands become gradually nar- 

 rowed down until we meet 

 them as the nucleated fibres, 

 0-0018-0-0023 mm. in dia- 

 meter, which have been already 

 mentioned. 



From these, again, is formed 

 a second network with toler- 

 ably broad rhomboidal or 

 elongated meshes, whose no- 

 dal points show nuclei with 

 distinct nucleoli. Pale fibres, 

 however, are also given off 

 directly from the "ground- 

 plexus" to the muscle cells. 

 This the "intermediate net- 

 work" (fig. 313) lies imme- 

 diately upon the layers of mus- 

 cular tissue, or between the latter. From it there pass off small fibres which 

 penetrate between the muscle fibres. These are only supplied with nuclei 

 at the commencement, and become 

 rapidly smaller, so that after repeated 

 subdivision they are reduced to 

 threads of '0005-0 -0003 mm. in 

 thickness. On the latter, as well at 

 their point of division as- elsewhere, 

 there occur elliptical, round, or other- 

 wise shaped swellings or granules. 



The last-mentioned fine fibres unite 

 once again to form a new, but this 

 time very close-meshed network, the 

 "intramuscular," whose varicose fib- 

 rillae occupy the narrow passages be- 

 tween the contractile cells. 



Finally, leaving this intramus- 

 cular interlacement, dark straight 

 fibres of extreme fineness pass off, 

 which are at the very most 0*0002 

 mm. in thickness. These penetrate 

 into the contractile cells, and ad- 

 vancing to the nucleus, terminate, 

 according to Frankzriliauser, in the 

 nucleolus. The number of terminal filaments which enter any one muscle 

 cell corresponds with the number of granules occurring in the nucleus 

 ( 163). 



Fig. 313. Ramification of nerves and termina- 

 tion in the muscular tunic of a small artery of 

 a frog; from Arnold. 



