TENDON AND BLOOD-VESSELS OF A MUSCLE. 



457 



all the sarcous substance, except the muscle rod, is doubly refractive or anisotropous, so that it 

 appears bright on a dark field when the Nicol's prisms are crossed, while under the same condi- 

 tions contracted muscle and dead muscle show alternate dark and light bands (Schafer).] 



The nuclei or muscle-corpuscles are found immediately under the sarcolemma in all 

 mammals, and their long axis lies in the long axis of the fibre (8 to 13 /x long, 3 to 4 n broad). 



[In the muscles of the frog, reptiles, and some other animals, e.g., the red muscles of the 

 rabbit and hare and in some muscles of birds, they lie in the substance of the fibre surrounded 

 by a small amount of protoplasm.] When they occur immediately under the sarcolemma they 

 are more or less flattened, and lie embedded in a small amount of protoplasm (fig. 302, 1 and 2, 

 K). They contain one or two nucleoli, and it is said that the protoplasm sends out fine 

 processes which unite with similar processes from adjoining corpuscles, so that, according to 

 this view, a branched protoplasmic network exists under the sarcolemma. [Each nucleus has a 

 reticulated appearance due to the presence of a plexus of fibrils, consisting of chromatin ; in its 

 meshes lies an achromatic substance. The nuclei are specially large in Otiorrhynchus planatus, 

 one of the beetles. Mitotic figures indicating division of the nuclei have been observed. The 

 nuclei are not seen in a perfectly fresh muscle, because, until they have undergone some change, 

 their refractive index is the same as that of the sarcous substance.] They become specially 

 evident after the addition of acetic acid. Histogenetically, they are the remainder of the cells 

 from which the muscular fibres were developed (fig. 302, 7). According to M. Schultze, the 

 sarcous substance is an intercellular substance differentiated and formed by their activity. 

 Perhaps they are the centres of nutrition for the mus- 

 cular fibres. In amphibians, birds, fishes, and reptiles, 

 they lie in the axis of the fibres between the fibrils. 



It is said that the protoplasm of the muscle-corpuscles 

 forms a fine network throughout the whole muscular 

 fibre, the transverse branches taking the course of the 

 lines of Krause or Dobie, and 

 the longitudinal branches run- 

 ning in the interstices between 

 Cohnheim's area (Retzius, 

 Bremer, Melland, fig. 306). 



Fig. 306. Fig. 307. Fig. 308. 



Fig. 306. Network in a muscular fibre. Fig. 307. Relation of a tendon, S, to its muscular 

 fibre. Fig. 308. Injected blood-vessels of a human muscle, a, small artery; b, vein; 

 c, capillaries, x 250. 



Eelation to Tendons. According to Toldt, the delicate connective-tissue elements, which 

 cover the several muscular fibres, pass from the ends of the latter directly into the connective- 

 tissue elements of the tendon. The end of the muscular fibre is perhaps united to the smooth 

 surface or hollow end of the tendon by means of a special cement ( Weismann fig. 307, S). In 

 arthropoda, the sarcolemma passes directly into and becomes ontinuous with the tendon {Leydig). 

 The tendon itself consists of longitudinally arranged bundles of white fibrous tissue with cells 

 teiidon cells embracing them. There is a loose capsule or sheath of connective-tissue the 

 peritendineum of Kollman surrounding the whole and carrying the blood-vessels, lymphatics, 

 and nerves. The tendons move in the tendon-sheaths, which are moistened by a mucous fluid. 

 In most situations, muscular fibres are attached by means of tendons to some fixed point, but 

 in other situations (face) the ends terminate between the connective-tissue elements of the 

 skin. 



[Blood-Vessels. Muscles, being very active organs, are richly supplied with blood. The 

 blood-supply of a muscle differs from some organs in not constituting an actual vascular unit, 



