804 OF THE STRUCTURE AND FUNCTIONS OF MUSCULAR TISSUE. 



transverse disks. In mammals the septal or intermediate and the collateral 

 disks appear to be fused together. 4. The isotropal layer between the second- 

 ary and transverse disks in Vertebrate has a thickness of 0.001 mm., and in 

 Arthropods of 0.0015. This is very soft, but still not fluid, as Kiihne 

 thought. 5. The layer of anisotropal substance consisting of two transverse 

 and a median disk (m). This layer after the action of many reagents ap- 

 pears to be formed of solid doubly refracting rod-like elements, the so-called 

 sarcous elements, muscle prisms or rodlets, which are imbedded in a softer, 

 singly refracting amorphous substance. (Fig. 285). The rods, according to 

 Engelmann, are certainly not preformed elements. The account given by 



FIG. 286. 



FIG. 285. 



n 



n, - 



7 



, 



'""M.I.MIIMIIII,,,,,,,,,,,,,,,,,,,,,,,,,!!!)!!!!!! 

 '"""MIIMIIIHU,, ,,,, ,,,,,|,, M ,III 



""'"ftffOiriMlflHMtmitlfflttMHMI 



FIG. 284. Structure of striated muscular fibre after Engelmann, 1 from Telephorus melanurus. 

 Cutaneous muscle from the abdomen, m, median disk ; n, secondary disk ; z, intermediate disk, mag- 

 nified 1000 diam. The sarcolemma is seen on the left side. Fm. 285, from Astacus fluviatilis. Heat 

 tetanus, n, secondary disk ; z, intermediate disk ; i, isotropous disk between transverse and secondary 

 disk; i, isotropous disk between secondary and intermediate disk; m, median disk; q, q, transverse 

 disk. The sarcous elements are swollen at their extremities, and at their centres. Magnified 1000 

 diam. 



FIG. 286. Muscular fibre undergoing contraction. R R, portions still at rest; p p, contraction pro- 

 ceeding; c, contracted portion ; a a', dim stripes ; b b' b", bright stripes; c c' c", Hues formed by rod- 

 heads. 



Sehiifer differs considerably from the foregoing. He describes a muscular 

 fibre as consisting of a ground substance, appearing at first sight to be com- 

 posed of a series of alternately dim and bright disks, and of a vast number 

 of minute rod-like particles, to which he applies the term muscle-rods, which 

 are closely arranged side by side, with their long axes parallel to the axis of 

 the fibre, so as to form by their juxtaposition as many series as there are 

 disks of dim substance in the fibre. The main part or shaft of each muscle- 

 rod is imbedded in and traverses a disk of dim substance, while the ends, 

 which are enlarged into little knobs or heads, extend into the bright disks. 

 These little knobs form the line of dots which has long been described as 

 existing in the middle of each bright stripe. When the fibre is somewhat 

 extended this line appears double, owing to the separation of the heads of 

 the two successive series of muscle-rods which meet in the middle of the 

 bright substance. In the state of absolute rest (R, Fig. 286) the rods are 

 uniformly cylindrical without terminal enlargements, and in this case only 



1 Pfliiger's Archiv, Bd. vii, p. 70. 



