STRUCTURE OF MUSCULAR TISSUE. 



805 



a longitudinal fibrillation is to be seen in the fibre, all trace of transverse 

 striping having disappeared. In the normal state of slight tension, however, 

 (p), the rod heads make their appearance, and with them the bright sub- 

 stance by which they are surrounded, so that the dim ground-substance now 

 presents a transversely striated aspect. In contraction of the muscle the 

 heads of the rods become enlarged at the expense of the shaft, the ends of 

 the several muscle-rods thus approaching one another, and forming with the 

 heads of the next series of muscle-rods, a dark transverse band crossing the 

 bright stripe. As the contraction proceeds the dark bands approximate to 

 one another, the bright borders encroach upon the dim stripe, which finally 

 disappears, so that its place is taken by a single transverse bright stripe (c). 

 Contracted muscle consequently shows alternate dark and bright stripes, the 

 former, however, being due to the enlarged juxtaposed extremities of the 

 rods, the light on the other hand being mainly composed of the ground-sub- 

 stance which has become accumulated in the intervals between their shafts. 

 Examined by polarized light, the muscle-rods give indications of being 

 isotropous or singly refracting, whilst the remainder of the fibre is anisotro- 

 pous. The latter is probably the true contractile part, whilst the rods are 

 merely elastic structures, serving to restore the fibre to its original length. 

 The muscles receive a free supply of blood, especially during action, 1 the 



FIG. 287. 



FIG. 288. 



FIG. 287. Diagram representative of 

 Mr. Schafer's view of the structure of 

 muscular fibre. 



1. Dim substance. 



2. Bright stripe. 



3. Muscle-rods. 



FIG. 288. Transverse section of one of the muscles of the thigh of the Lacerta agilis, made whilst 

 frozen, and magnified 400 diameters. N, nerve. M, muscular fibre, surrounded by portions of six 

 others, a, Nucleus of the nerve-sheath ; b, nucleus of the sarcoleinrua; c, section of nucleus of termi- 

 nal plate of nerve ; d, transverse section of terminal plate, surrounded by granular material ; e, trans- 

 verse section of muscle-nuclei; /, fine fat-drops. The angular dark particles are sections of groups of 

 sarcous elements; the clear intervening spaces represent the fluid isotropal part of the muscle-sub- 

 stance. 



capillary vessels being arranged in oblong meshes ; but their lymphatics are 

 either altogether absent or exceedingly few in number. 2 The mode of ter- 

 mination of the nerves in muscle has also recently been the subject of much 

 investigation. 3 According to Kuhne and Engelmann, the motor nerves 

 divide and subdivide till the fibres run alone or only in bundles of two or 

 three on the outside of the muscular fibres. After a short course, however, 

 they penetrate the sarcolemma, losing at the same time their sheath, which 



1 Sczelkow, Centralblatt, 1870, p. 691. 



! Teichmann, Das Saugader System, 1861, p. 100. 



3 See Kuhne, Ueber die peripheric Endorgane der Motor Nerven, 1862; Engel- 

 mann, T. W., Untersuch. ub. d. Zusammenhang v. Nerv- u. Muskel-faser, Leipzig, 

 1863; Kolliker, Croonian Lecture, .Ib52; Beale, Archives of Medicine, vol. iii, 

 1862, p. 246; Philosophical Transactions, 1863; Croonian Lecture, 1865; and Distri- 

 bution of Nerves to Voluntary Muscles : an Anatomical Controversy. Pamphlet, 

 Churchill, 1865. 



